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19-2882; Rev 0; 5/03
KIT ATION EVALU BLE AVAILA
Six-Channel, High-Efficiency, Digital Camera Power Supplies
General Description Features
o 95% Efficient Step-Up DC-to-DC Converter o 0.7V Minimum Input Voltage o Main DC-to-DC Configurable as Either Step-Up or Step-Down o Combine Step-Up and Step-Down for 90% Efficient Boost-Buck o 95% Efficient Step-Down for DSP Core o Regulate LED Current for Four, Six, or More LEDs o Open LED Overvoltage Protection o Transformerless Inverting Controller (MAX1567) o Three Extra PWM Controllers (Two on the MAX1567) o Up to 1MHz Operating Frequency o 1A Shutdown Mode o Soft-Start and Overload Protection o Compact 40-Pin 6mm x 6mm Thin QFN Package
MAX1566/MAX1567
The MAX1566/MAX1567 provide a complete powersupply solution for digital cameras. They improve performance, component count, and size compared to conventional multichannel controllers in 2-cell AA, 1-cell lithium-ion (Li+), and dual-battery designs. On-chip MOSFETs provide up to 95% efficiency for critical power supplies, while additional channels operate with external FETs for optimum design flexibility. This optimizes overall efficiency and cost, while also reducing board space. The MAX1566/MAX1567 include six high-efficiency DCto-DC conversion channels: * Step-up DC-to-DC converter with on-chip power FETs * Main DC-to-DC converter with on-chip FETs, configurable to step either up or down * Step-down core DC-to-DC converter with on-chip FETs * DC-to-DC controller for white LEDs or other output * Extra DC-to-DC controller (typically for LCD); two extra controllers on the MAX1566 * Transformerless inverting DC-to-DC controller (typically for negative CCD bias) on the MAX1567 All DC-to-DC channels operate at one fixed frequency settable from 100kHz to 1MHz to optimize size, cost, and efficiency. Other features include soft-start, power-OK outputs, and overload protection. The MAX1566/ MAX1567 are available in space-saving 40-pin thin QFN packages. An evaluation kit is available to expedite designs.
Ordering Information
PART TEMP RANGE PIN-PACKAGE 40 Thin QFN 6mm x 6mm 40 Thin QFN 6mm x 6mm AUX2 FUNCTION Step-up controller Inverting controller
MAX1566ETL -40C to +85C MAX1567ETL -40C to +85C
Applications
FB3L
Pin Configuration
GND ON3 CC3 DL1 DL3 DL2 FB2
30 CC2 29 ON2 28 PVM 27 LXM 26 PGM 25 PVSU 24 LXSU 23 PGSU 22 OSC 21 SDOK 11 12 13 14 15 16 17 18 19 20
PDAs
Typical Operating Circuit
FB3H 1
40 39 38 37 36 35 34 33 32 31
Li+ OR 2AA BATTERY INPUT MAX1567 STEP-UP MAIN DC-TO-DC ONSU ONM ONSD ON3(LED) ON1 ON2 STEP-DN AUX3 AUX1 AUX2 CCD/LCD + 15V CCD - 7.5V LEDS SYSTEM 5V 3.3V LOGIC 1.8V CORE
CC1 2 FB1 3 ON1 4 PGSD 5 LXSD 6 PVSD 7 ONSD 8 FBSD 9 CCSD 10 ONM REF SUSD FBM CCSU FBSU ONSU SCF AUX1OK CCM
MAX1566/MAX1567
6mm x 6mm THIN QFN
________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
PV
TOP VIEW
INDL2
Digital Cameras
Six-Channel, High-Efficiency, Digital Camera Power Supplies MAX1566/MAX1567
ABSOLUTE MAXIMUM RATINGS
PV, PVSU, SDOK, AUX1OK, SCF, ON_, FB_, SUSD to GND ....................................................... -0.3V to +6V PG_ to GND...........................................................-0.3V to +0.3V DL1, DL3, INDL2, PVM, PVSD to GND ...-0.3V to (PVSU + 0.3V) DL2 to GND ............................................-0.3V to (INDL2 + 0.3V) LXSU Current (Note 1) ..........................................................3.6A LXM Current (Note 1) ............................................................3.6A LXSD Current (Note 1) ........................................................2.25A REF, OSC, CC_ to GND...........................-0.3V to (PVSU + 0.3V) Continuous Power Dissipation (TA = +70C) 40-Pin Thin QFN (derate 26.3mW/C above +70C) .2105mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
Note 1: LXSU has internal clamp diodes to PVSU and PGSU, LXM has internal clamp diodes to PVM and PGM, and LXSD has internal clamp diodes to PVSD and PGSD. Applications that forward bias these diodes should take care not to exceed the devices' power dissipation limits.
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VPVSU = VPV = VPVM = VPVSD = VINDL2 = 3.6V, TA = 0C to +85C, unless otherwise noted.)
PARAMETER GENERAL Input Voltage Range Step-Up Minimum Startup Voltage (Note 2) Shutdown Supply Current into PV Supply Current into PV with StepUp Enabled Supply Current into PV with StepUp and Step-Down Enabled Supply Current into PV with StepUp and Main Enabled Total Supply Current from PV and PVSU with Step-Up and One AUX Enabled REFERENCE Reference Output Voltage Reference Load Regulation Reference Line Regulation OSCILLATOR OSC Discharge Trip Level OSC Discharge Resistance OSC Discharge Pulse Width OSC Frequency ROSC = 47k, COSC = 100pF Rising edge OSC = 1.5V, IOSC = 3mA 1.225 1.25 52 150 500 1.275 80 V ns kHz IREF = 20A 10A < IREF < 200A 2.7 < PVSU < 5.5V 1.23 1.25 4.5 1.3 1.27 10 5 V mV mV (Note 2) ILOAD < 1mA, TA = +25C; startup voltage tempco is -2300ppm/C (typ) (Note 3) PV = 3.6V ONSU = 3.6V, FBSU = 1.5V (does not include switching losses) ONSU = ONSD = 3.6V, FBSU = 1.5V, FBSD = 1.5V (does not include switching losses) ONSU = ONM = 3.6V, FBSU = 1.5V, FBSD = 1.5V (does not include switching losses) ONSU = ON1 = 3.6V, FBSU = 1.5V, FB2 = 1.5V (does not include switching losses) 0.7 0.9 0.1 300 450 450 5.5 1.1 10 450 700 700 V V A A A A CONDITIONS MIN TYP MAX UNITS
400
650
A
2
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Six-Channel, High-Efficiency, Digital Camera Power Supplies
ELECTRICAL CHARACTERISTICS (continued)
(VPVSU = VPV = VPVM = VPVSD = VINDL2 = 3.6V, TA = 0C to +85C, unless otherwise noted.)
PARAMETER STEP-UP DC-TO-DC Step-Up Startup-to-Normal Operating Threshold Step-Up Startup-to-Normal Operating Threshold Hysteresis Step-Up Voltage Adjust Range Start Delay of ONSD, ONM, ON1, ON2, and ON3 after SU in Regulation FBSU Regulation Voltage FBSU to CCSU Transconductance FBSU Input Leakage Current Idle ModeTM Trip Level Current-Sense Amplifier Transresistance Step-Up Maximum Duty Cycle PVSU Leakage Current LXSU Leakage Current Switch On-Resistance N-Channel Current Limit P-Channel Turn-Off Current Startup Current Limit Startup tOFF Startup Frequency MAIN DC-TO-DC CONVERTER Main Step-Up Voltage Adjust Range Main Step-Down Voltage Adjust Range PVM Undervoltage Lockout in Step-Down Mode Regulation Voltage FBM to CCM Transconductance FBM Input Leakage Current Idle Mode Trip Level Current-Sense Amplifier Transresistance FBM = CCM FBM = 1.25V Step-up mode (SUSD = PVSU) Step-down mode (SUSD = GND) Step-up mode (SUSD = PVSU) Step-down mode (SUSD = GND) SUSD = PVSU SUSD = GND, PVM must be greater than output (Note 6) SUSD = GND (Note 6) 3 2.45 2.45 1.231 80 -100 2.5 1.25 135 0.01 150 100 0.25 0.5 5.5 5.00 2.55 1.269 185 +100 V V V V S nA mA V/A PVSU = 1.8V (Note 5) PVSU = 1.8V PVSU = 1.8V FBSU = 1V VLX = 0V, PVSU = 3.6V VLX = VOUT = 3.6V N channel P channel 1.8 80 FBSU = CCSU FBSU = 1.25V 1.231 80 -100 3.0 1024 1.25 135 0.01 150 0.275 85 0.1 0.1 95 150 2.1 20 450 700 200 90 5 5 150 250 2.4 1.269 185 +100 Rising edge or falling edge (Note 4) 2.30 2.5 80 5.5 2.65 V mV V OSC cycles V S nA mA V/A % A A m A mA mA ns kHz CONDITIONS MIN TYP MAX UNITS
MAX1566/MAX1567
Idle Mode is a trademark of Maxim Integrated Products, Inc. _______________________________________________________________________________________ 3
Six-Channel, High-Efficiency, Digital Camera Power Supplies MAX1566/MAX1567
ELECTRICAL CHARACTERISTICS (continued)
(VPVSU = VPV = VPVM = VPVSD = VINDL2 = 3.6V, TA = 0C to +85C, unless otherwise noted.)
PARAMETER Maximum Duty Cycle (Note 6) LXM Leakage Current Switch On-Resistance Main Switch Current Limit Synchronous Rectifier Turn-Off Current Soft-Start Interval STEP-DOWN DC-TO-DC CONVERTER Step-Down Output-Voltage Adjust PVSD must be greater than output (Note 7) Range FBSD Regulation Voltage FBSD to CCSD Transconductance FBSD Input Leakage Current Idle Mode Trip Level Current-Sense Amplifier Transresistance LXSD Leakage Current Switch On-Resistance P-Channel Current Limit N-Channel Turn-Off Current Soft-Start Interval SDOK Output Low Voltage SDOK Leakage Current INDL2 Undervoltage Lockout Maximum Duty Cycle FB1, FB2 (MAX1566), FB3H Regulation Voltage FB2 (MAX1567) Inverter Regulation Voltage FB_ = 1V 0.1mA into SDOK ONSU = GND VLXSD = 0 to 3.6V, PVSU = 3.6V N channel P channel 0.65 FBSD = CCSD FBSD = 1.25V 1.25 1.231 80 -100 1.25 135 0.1 100 0.5 0.1 95 150 0.77 20 2048 0.01 0.01 0.1 1 5 150 250 0.90 5.00 1.269 185 +100 V V S nA mA V/A A m A mA OSC cycles V A CONDITIONS Step-up mode (SUSD = PVSU) Step-down mode (SUSD = GND) VLXM = 0 to 3.6V, PVSU = 3.6V N channel P channel Step-up mode (SUSD = PVSU) Step-down mode (SUSD = GND) Step-up mode (SUSD = PVSU) Step-down mode (SUSD = GND) 1.8 0.70 MIN 80 TYP 85 95 0.1 95 150 2.1 0.8 20 20 4096 5 150 250 2.4 0.95 MAX 90 UNITS % A m A mA OSC cycles
AUX1, 2, 3 DC-TO-DC CONTROLLERS 2.45 80 1.231 -0.01 2.5 85 1.25 0 2.55 90 1.269 +0.01 V % V V
4
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Six-Channel, High-Efficiency, Digital Camera Power Supplies
ELECTRICAL CHARACTERISTICS (continued)
(VPVSU = VPV = VPVM = VPVSD = VINDL2 = 3.6V, TA = 0C to +85C, unless otherwise noted.)
PARAMETER FB3L Regulation Voltage AUX1, AUX2 FB to CC Transconductance AUX3 FBL or FBH to CC Transconductance FB_ Input Leakage Current DL_ Driver Resistance DL_ Drive Current Soft-Start Interval AUX1OK Output Low Voltage AUX1OK Leakage Current OVERLOAD PROTECTION Overload Protection Fault Delay SCF Leakage Current SCF Output Low Voltage THERMAL-LIMIT PROTECTION Thermal Shutdown Thermal Hysteresis LOGIC INPUTS (ON_, SUSD) ONSU Input Low Level 1.1V < PVSU < 1.8V 1.8V < PVSU < 5.5V 1.1V < PVSU < 1.8V ONSU Input High Level 1.8V < PVSU < 5.5V ONM, ONSD, ON1, ON2, ON3, SUSD Input Low Level ONM, ONSD, ON1, ON2, ON3, SUSD Input High Level SUSD Input Leakage ON_ Impedance to GND 2.7V < PVSU < 5.5V (Note 8) 2.7V < PVSU < 5.5V (Note 8) 1.6 0.1 330 1 (PVSU - 0.2) 1.6 0.4 V V A k 0.2 0.4 V 160 20 C C ONSU = PVSU, FBSU = 1.5V 0.1mA into SCF 100,000 0.1 0.01 1 0.1 OSC cycles A V 0.1mA into AUX1OK ONSU = GND Output high or low Sourcing or sinking CONDITIONS MIN 0.19 80 50 -100 TYP 0.2 135 100 0.1 2.5 0.5 4096 0.01 0.01 0.1 1 MAX 0.21 185 150 +100 7 UNITS V S S nA A OSC cycles V A
MAX1566/MAX1567
V
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5
Six-Channel, High-Efficiency, Digital Camera Power Supplies MAX1566/MAX1567
ELECTRICAL CHARACTERISTICS
(VPVSU = VPV = VPVM = VPVSD = VINDL2 = 3.6V, TA = -40C to +85C, unless otherwise noted.)
PARAMETER GENERAL Input Voltage Range Step-Up Minimum Startup Voltage (Note 2) Shutdown Supply Current into PV Supply Current into PV with StepUp Enabled Supply Current into PV with StepUp and Step-Down Enabled Supply Current into PV with StepUp and Main Enabled Total Supply Current from PV and PVSU with Step-Up and One AUX Enabled REFERENCE Reference Output Voltage Reference Load Regulation Reference Line Regulation OSCILLATOR OSC Discharge Trip Level OSC Discharge Resistance Step-Up Startup-to-Normal Operating Threshold Step-Up Voltage Adjust Range FBSU Regulation Voltage FBSU to CCSU Transconductance FBSU Input Leakage Current Step-Up Maximum Duty Cycle PVSU Leakage Current LXSU Leakage Current Switch On-Resistance N-Channel Current Limit MAIN DC-TO-DC CONVERTER Main Step-Up Voltage Adjust Range SUSD = PVSU 3.0 5.5 V FBSU = CCSU FBSU = 1.25V FBSU = 1V VLX = 0V, PVSU = 3.6V VLX = VOUT = 3.6V N channel P channel 1.8 Rising edge OSC = 1.5V, IOSC = 3mA 1.225 1.275 80 V IREF = 20A 10A < IREF < 200A 2.7V < PVSU < 5.5V 1.23 1.27 10 5 V mV mV (Note 2) ILOAD < 1mA, TA = +25C; startup voltage tempco is -2300ppm/C (typ) (Note 3) PV = 3.6V ONSU = 3.6V, FBSU = 1.5V (does not include switching losses) ONSU = ONSD = 3.6V, FBSU = 1.5V, FBSD = 1.5V (does not include switching losses) ONSU = ONM = 3.6V, FBSU = 1.5V, FBSD = 1.5V (does not include switching losses) ONSU = ON1 = 3.6V, FBSU = 1.5V, FB2 = 1.5V (does not include switching losses) 0.7 5.5 1.1 10 400 600 600 V V A A A A CONDITIONS MIN MAX UNITS
550
A
STEP-UP DC-TO-DC CONVERTER Rising edge or falling edge (Note 4) 2.30 3.0 1.231 80 -100 80 2.65 5.5 1.269 185 +100 90 5 5 150 250 2.4 V V V S nA % A A m A
6
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Six-Channel, High-Efficiency, Digital Camera Power Supplies
ELECTRICAL CHARACTERISTICS (continued)
(VPVSU = VPV = VPVM = VPVSD = VINDL2 = 3.6V, TA = -40C to +85C, unless otherwise noted.)
PARAMETER Main Step-Down Voltage Adjust Range PVM Undervoltage Lockout in Step-Down Mode Regulation Voltage FBM to CCM Transconductance FBM Input Leakage Current Maximum Duty Cycle LXM Leakage Current Switch On-Resistance Main Switch Current Limit FBM = CCM FBM = 1.25V Step-up mode (SUSD = PVSU), step-down mode (SUSD = GND) (Note 6) VLXM = 0 to 3.6V, PVSU = 3.6V N channel P channel Step-up mode (SUSD = PVSU) Step-down mode (SUSD = GND) 1.8 0.70 CONDITIONS SUSD = GND, PVM must be greater than output (Note 6) SUSD = GND (Note 6) MIN 2.45 2.45 1.225 80 -100 80 MAX 5.00 2.55 1.275 185 +100 90 5 150 250 2.4 0.95 UNITS V V V S nA % A m A
MAX1566/MAX1567
STEP-DOWN DC-TO-DC CONVERTER Step-Down Output Voltage Adjust Range FBSD Regulation Voltage FBSD to CCSD Transconductance FBSD Input Leakage Current LXSD Leakage Current Switch On-Resistance P-Channel Current Limit SDOK Output Low Voltage SDOK Leakage Current INDL2 Undervoltage Lockout Maximum Duty Cycle FB1, FB2 (MAX1566), FB3H Regulation Voltage FB2 (MAX1567) Inverter Regulation Voltage FB3L Regulation Voltage AUX1, AUX2 FB to CC Transconductance FB_ = 1V 0.1mA into SDOK ONSU = GND 2.45 80 1.225 -0.01 0.19 80 FBSD = CCSD FBSD = 1.25V VLXSD = 0 to 3.6V, PVSU = 3.6V N channel P channel 0.65 PVSD must be greater than output (Note 7) 1.25 1.225 80 -100 5.00 1.275 185 +100 5 150 250 0.90 0.1 1 2.55 90 1.275 +0.01 0.21 185 V V S nA A m A V A V % V V V S
AUX1, 2, 3 DC-TO-DC CONTROLLERS
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7
Six-Channel, High-Efficiency, Digital Camera Power Supplies MAX1566/MAX1567
ELECTRICAL CHARACTERISTICS (continued)
(VPVSU = VPV = VPVM = VPVSD = VINDL2 = 3.6V, TA = -40C to +85C, unless otherwise noted.)
PARAMETER AUX3 FBL or FBH to CC Transconductance FB_ Input Leakage Current DL_ Driver Resistance AUX1OK Output Low AUX1OK Leakage Current OVERLOAD PROTECTION SCF Leakage Current SCF Output Low Voltage LOGIC INPUTS (ON_, SUSD) ONSU Input Low Level 1.1V < PVSU < 1.8V 1.8V < PVSU < 5.5V 1.1V < PVSU < 1.8V ONSU Input High Level 1.8V < PVSU < 5.5V ONM, ONSD, ON1, ON2, ON3, SUSD Input Low Level ONM, ONSD, ON1, ON2, ON3, SUSD Input High Level SUSD Input Leakage 2.7V < PVSU < 5.5V (Note 8) 2.7V < PVSU < 5.5V (Note 8) 1.6 1 (PVSU - 0.2) 1.6 0.4 V V A 0.2 0.4 v ONSU = PVSU, FBSU = 1.5V 0.1mA into SCF 1 0.1 A V Output high or low 0.1mA into AUX1OK ONSU = GND CONDITIONS MIN 35 -100 MAX 150 +100 7 0.1 1 UNITS S nA V A
V
Note 2: The MAX1566/MAX1567 are powered from the step-up output (PVSU). An internal low-voltage startup oscillator drives the step-up starting at approximately 0.9V until PVSU reaches approximately 2.5V. When PVSU reaches 2.5V, the main control circuitry takes over. Once the step-up is up and running, it can maintain operation with very low input voltages; however, output current is limited. Note 3: Since the device is powered from PVSU, a Schottky rectifier, connected from the battery to PVSU, is required for low-voltage startup. Note 4: The step-up regulator is in startup mode until this voltage is reached. Do not apply full load current during startup. A powerOK output can be used with an external PFET to gate the load until the step-up is in regulation. See the AUX1OK, SDOK, and SCF Connections section. Note 5: The step-up current limit in startup refers to the LXSU switch current limit, not the output current limit. Note 6: If the main converter is configured as a step-up (SUSD = PVSU), the P-channel synchronous rectifier is disabled until the 2.5V normal operation threshold has been exceeded. If the main converter is configured as a step-down (SUSD = GND), all step-down operation is locked out until the normal operation threshold has been exceeded. When the main is configured as a step-down, operation in dropout (100% duty cycle) can only be maintained for 100,000 OSC cycles before the output is considered faulted, triggering global shutdown. Note 7: Operation in dropout (100% duty cycle) can only be maintained for 100,000 OSC cycles before the output is considered faulted, triggering global shutdown. Note 8: ONM, ONSD, ON1, ON2, and ON3 are disabled until 1024 OSC cycles after PVSU reaches 2.7V.
8
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Six-Channel, High-Efficiency, Digital Camera Power Supplies
Typical Operating Characteristics
(TA = +25C, unless otherwise noted.)
MAIN (STEP-UP) EFFICIENCY vs. LOAD CURRENT
MAX1566/67 toc02
MAX1566/MAX1567
STEP-UP EFFICIENCY vs. LOAD CURRENT
MAX1566/67 toc01
BOOST-BUCK EFFICIENCY (SU + MAIN AS STEP-DOWN) vs. LOAD CURRENT
90 80 70 EFFICIENCY (%) 60 50 40 30 20 VM = 3.3V VSU = 5V 1 10 100 1000 VIN = 4.5V VIN = 3.8V VIN = 3.2V VIN = 2.5V
MAX1566/67 toc03
100 90 80 70 EFFICIENCY (%) 60 50 40 30 20 10 0 1 10 100 LOAD CURRENT (mA) VSU = 5V VIN = 4.5V VIN = 3.8V VIN = 3.2V VIN = 2.5V VIN = 2.0V VIN = 1.5V
100 90 80 70 EFFICIENCY (%) 60 50 40 30 20 10 0 1 10 100 VM = 3.3V VIN = 3.2V VIN = 2.5V VIN = 2.0V VIN = 1.5V
100
10 0
1000
1000
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
STEP-DOWN EFFICIENCY vs. LOAD CURRENT
MAX1566/67 toc04
BOOST-BUCK EFFICIENCY (SU + SD) vs. LOAD CURRENT
MAX1566/67 toc05
90 80 70 EFFICIENCY (%) 60 50 40 30 20 10 0 1 10 100 SD = 1.8V SD INPUT CONNECTED TO BATT VIN = 2.5V VIN = 3.0V VIN = 3.8V VIN = 4.5V
90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 1 10 100 VSU = 3.3V SD = 1.8V VIN = 3.2V VIN = 2.5V VIN = 2.0V VIN = 1.5V
95 90 85
VM = 3.3V IOUTVM = 200mA SU = 5V, IOUTSU = 500mA
EFFICIENCY (%)
AUX2 = 8V, IOUT2 = 100mA 80 75 70 SU + SD, IOUT3 = 350mA
1000
1000
1.5
2.5
3.5
4.5
LOAD CURRENT (mA)
LOAD CURRENT (mA)
INPUT VOLTAGE (V)
AUX EFFICIENCY vs. LOAD CURRENT
MAX1566/67 toc07
AUX EFFICIENCY vs. LOAD CURRENT
MAX1566/67 toc08
MAX1567 AUX2 EFFICIENCY vs. LOAD CURRENT
90 80 70 EFFICIENCY (%)
MAX1566/67 toc09
90 80 70 EFFICIENCY (%) 60 50 40 30 20 10 VOUT_AUX = 5V 0 1 10 100 VIN = 4.5V VIN = 3.8V VIN = 3.0V VIN = 2.0V VIN = 1.5V
100 90 80 EFFICIENCY (%) 70 60 50 40 30 1 10 LOAD CURRENT (mA) VOUT_AUX = 15V VIN = 4.5V VIN = 3.8V VIN = 3.0V VIN = 2.0V VIN = 1.5V
100
60 50 40 30 20 10 0 1
VIN = 2.5V VIN = 3.0V VIN = 3.8V VIN = 4.5V
VAUX2 = -7.5V 10 100 1000
1000
100
LOAD CURRENT (mA)
LOAD CURRENT (mA)
_______________________________________________________________________________________
MAX1566/67 toc06
100
EFFICIENCY vs. INPUT VOLTAGE
100
100
9
Six-Channel, High-Efficiency, Digital Camera Power Supplies MAX1566/MAX1567
Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.)
NO-LOAD INPUT CURRENT vs. INPUT VOLTAGE (SWITCHING)
MAX1566/67 toc10
MINIMUM STARTUP VOLTAGE vs. LOAD CURRENT (OUTSU)
MAX1566/67 toc11
REFERENCE VOLTAGE vs. TEMPERATURE
MAX1566/67 toc12
3.0
3.5 MINIMUM STARTUP VOLTAGE (V) 3.0 2.5 2.0 1.5 1.0 0.5 0.0 WITH NO SCHOTTKY RECTIFER FROM BATT TO PVSU
1.254
2.5 INPUT CURRENT (mA) VSU = 5.0V + VM = 3.3V 2.0 VSU = 5.0V + VSD = 1.8V
REFERENCE VOLTAGE (V) 0 200 400 600 800 1000
1.251
1.248
1.5
1.246
1.0 VSU = 5.0V ONLY 0.5 0 1 2 3 4 5 INPUT VOLTAGE (V)
1.243 -50 -25 0 25 50 75 100 LOAD CURRENT (mA) TEMPERATURE (C)
REFERENCE VOLTAGE vs. REFERENCE LOAD CURRENT
MAX1566/67 toc13
OSCILLATOR FREQUENCY vs. ROSC
MAX1566/7 toc14
SWITCHING FREQUENCY vs. TEMPERATURE
315 314 313 312 311 310 309 308 307 306 305 304 303 302 301 300 -50 -25 0 25 50 75 TEMPERATURE (C)
MAX1566/67 toc15
1.250 1.249 REFERENCE VOLTAGE (V) 1.248 1.247 1.246 1.245 1.244 0 50 100 150 200 250
OSCILLATOR FREQUENCY (kHz)
1000 800 600 400 200 0
300
1
10 ROSC (k)
100
1000
SWITCHING FREQUENCY (kHz)
COSC = 470pF COSC = 330pF COSC = 220pF COSC = 100pF COSC = 47pF
100
REFERENCE LOAD CURRENT (A)
AUX_ MAXIMUM DUTY CYCLE vs. FREQUENCY
MAX1566/67 toc16
STEP-UP STARTUP WAVEFORMS
MAX1566/67 toc17
STEP-UP STARTUP WAVEFORMS
MAX1566/67 toc18
88 87 MAXIMUM DUTY CYCLE (%) 86 85 84 83 82 81 80 0 200 400 600 800 1000 COSC = 100pF WHEN THIS DUTY CYCLE IS EXCEEDED FOR 100,000 CLOCK CYCLES, THE MAX1566/MAX1567 SHUT DOWN
ONSU 2V/div 0V 0V VSU = 3.3V 5V/div IOUT_SU 100mA/div 0V 0V
ONSU 2V/div VSU = 5V 5V/div IOUT_SU 100mA/div
0A
0A
0A VIN = 2V, VSU = 3.3V 1200 100s/div FREQUENCY (kHz)
IIN 1A/div
0A VIN = 3.0V, VSU = 5V 100s/div
IIN 1A/div
10
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Six-Channel, High-Efficiency, Digital Camera Power Supplies
Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.)
MAX1566/MAX1567
MAIN (STEP-UP MODE) AND STEP-DOWN STARTUP WAVEFORMS
MAX1566/67 toc19
MAIN (STEP-DOWN MODE) AND STEP-DOWN STARTUP WAVEFORMS
MAX1566/67 toc20
0V 0V
ONSU = ONSD = ONM 2V/div VSU 5V/div VSD 1V/div VM (MAIN AS BOOST) 2V/div VIN = 3.0V 2ms/div
0V
ONSU = ONM = ONSD 2V/div VSU 2V/div VSD 2V/div VM 2V/div
0V 0V
0V 0V
0V (MAIN AS STEP-DOWN) 2ms/div
STEP-UP LOAD TRANSIENT RESPONSE
MAX1566/67 toc21
MAIN (STEP-UP MODE) LOAD TRANSIENT RESPONSE
MAX1566/67 toc22
0V
VSU AC-COUPLED 100mV/div
0V
VM AC-COUPLED 100mV/div
0A VIN = 3.0V, VSU = 5V 1ms/div
ISU 200mA/div
0A
(MAIN AS STEP-UP) VIN = 3.0V, VM = 3.3V 1ms/div
IM 100mA/div
MAIN (STEP-DOWN MODE) LOAD TRANSIENT RESPONSE
MAX1566/67 toc23
STEP-DOWN TRANSIENT RESPONSE
MAX1566/67 toc24
0V
VM AC-COUPLED 200mV/div
0V
VSD AC-COUPLED 20mV/div
0A (MAIN AS STEP-DOWN FROM SU) VIN = 3.0V, VM = 3.3V 1ms/div
IM 200mA/div
0A VIN = 3.0V, VSD = 1.8V 1ms/div
ISD 100mA/div
______________________________________________________________________________________
11
Six-Channel, High-Efficiency, Digital Camera Power Supplies MAX1566/MAX1567
Pin Description
PIN NAME FUNCTION AUX3 Controller Voltage Feedback Input. Connect a resistive voltage-divider from the step-up converter output to FBH to set the output voltage. The feedback threshold is 1.25V. This pin is high impedance in shutdown. FB3H can provide conventional voltage feedback (with FB3L grounded) or open-LED protection in white LED drive circuits. AUX1 Controller Compensation Node. Connect a series resistor-capacitor from this pin to GND to compensate the converter control loop. This pin is actively driven to GND in shutdown, overload, and thermal limit. See the AUX Compensation section. AUX1 Controller Feedback Input. The feedback threshold is 1.25V. This pin is high impedance in shutdown. AUX1 Controller On/Off Input. Logic high = on; however, turn-on is locked out until 1024 OSC cycles after the step-up has reached regulation. This pin has an internal 330k pulldown resistance to GND. Power Ground. Connect all PG_ pins to GND with short wide traces as close to the IC as possible. Step-Down Converter Switching Node. Connect to the inductor of the step-down converter. LXSD is high impedance in shutdown. Step-Down Converter Input. Bypass to GND with a 1F ceramic capacitor. The step-down efficiency is measured from this input. Step-Down Converter On/Off Control Input. Logic high = on; however, turn-on is locked out until 1024 OSC cycles after the step-up has reached regulation. This pin has an internal 330k pulldown resistance to GND. Step-Down Converter Feedback Input. The feedback threshold is 1.25V. This pin is high impedance in shutdown. Step-Down Converter Compensation Node. Connect a series resistor-capacitor from this pin to GND for compensating the converter control loop. This pin is actively driven to GND in shutdown, overload, and thermal limit. See the Step-Down Compensation section. Configures the Main Converter as a Step-Up or a Step-Down. This function must be hardwired. Onthe-fly changes are not allowed. With SUSD connected to PV, the main is configured as a step-up and PVM is the converter output. With SUSD connected to GND, the main is configured as a stepdown and PVM is the power input. Main Converter Compensation Node. Connect a series resistor-capacitor from this pin to GND for compensating the converter control loop. This pin is actively driven to GND in shutdown, overload, and thermal limit. See the Step-Up Compensation section when the main is used in step-up mode and the Step-Down Compensation section when the main is used in step-down mode. Main Converter Feedback Input. The feedback threshold is 1.25V. This pin is high impedance in shutdown. The main output voltage must not be set higher than the step-up output. On/Off Control for the Main DC-to-DC Converter. Logic high = on; however, turn-on is locked out until 1024 OSC cycles after the step-up has reached regulation. This pin has an internal 330k pulldown resistance to GND. SUSD pin configures the main converter as a step-up or step-down. Reference Output. Bypass REF to GND with a 0.1F or greater capacitor. The maximum-allowed REF load is 200A. REF is actively pulled to GND when the step-up is shut down (all converters turn off).
1
FB3H
2
CC1
3 4 5 6 7
FB1 ON1 PGSD LXSD PVSD
8
ONSD
9
FBSD
10
CCSD
11
SUSD
12
CCM
13
FBM
14
ONM
15
REF
12
______________________________________________________________________________________
Six-Channel, High-Efficiency, Digital Camera Power Supplies
Pin Description (continued)
PIN 16 NAME CCSU FUNCTION Step-Up Converter Compensation Node. Connect a series resistor-capacitor from this pin to GND for compensating the converter control loop. This pin is actively driven to GND in shutdown, overload, and thermal limit. See the Step-Up Compensation section. Step-Up Converter Feedback Input. The feedback threshold is 1.25V. This pin is high impedance in shutdown. Step-Up Converter On/Off Control. Logic high = on. All other ON_ pins are locked out until 1024 OSC cycles after the step-up DC-to-DC converter output has reached its final value. This pin has an internal 330k pulldown resistance to GND. Open-Drain, Active-Low, Short-Circuit Flag Output. SCF goes open when overload protection occurs and during startup. SCF can drive high-side PFET switches connected to one or more outputs to completely disconnect the load when the channel turns off in response to a logic command or an overload. See the Status Outputs (SDOK, AUX1OK, SCF) section. Open-Drain, Active-Low, Power-OK Signal for AUX1 Controller. AUX1OK goes low when the AUX1 controller has successfully completed soft-start. AUX1OK goes high impedance in shutdown, overload, and thermal limit. Open-Drain, Active-Low, Power-OK Signal for Step-Down Converter. SDOK goes low when the stepdown has successfully completed soft-start. SDOK goes high impedance in shutdown, overload, and thermal limit. Oscillator Control. Connect a timing capacitor from OSC to GND and a timing resistor from OSC to PVSU (or other DC voltage) to set the oscillator frequency between 100kHz and 1MHz. See the Setting the Switching Frequency section. This pin is high impedance in shutdown. Power Ground. Connect all PG_ pins to GND with short wide traces as close to the IC as possible. Step-Up Converter Switching Node. Connect to the inductor of the step-up converter. LXSU is high impedance in shutdown. Power Output of the Step-Up DC-to-DC Converter. PVSU can also power other converter channels. Connect PVSU and PV together. Power Ground. Connect all PG_ pins to GND with short wide traces as close to the IC as possible. Main Converter Switching Node. Connect to the inductor of the main converter (can be configured as a step-up or step-down by SUSD). LXM is high impedance in shutdown. When SUSD = PVSU, the main converter is configured as a step-up and PVM is the main output. When SUSD = GND, the main is configured as a step-down and PVM is the power input. AUX2 Controller On/Off Input. Logic high = on; however, turn-on is locked out until 1024 OSC cycles after the step-up has reached regulation. This pin has an internal 330k pulldown resistance to GND. AUX2 Controller Compensation Node. Connect a series resistor-capacitor from this pin to GND to compensate the converter control loop. This pin is actively driven to GND in shutdown, overload, and thermal limit. See the AUX Compensation section.
MAX1566/MAX1567
17
FBSU
18
ONSU
19
SCF
20
AUX1OK
21
SDOK
22 23 24 25 26 27 28 29
OSC PGSU LXSU PVSU PGM LXM PVM ON2
30
CC2
______________________________________________________________________________________
13
Six-Channel, High-Efficiency, Digital Camera Power Supplies MAX1566/MAX1567
Pin Description (continued)
PIN NAME AUX2 Controller Feedback Input. This pin is high impedance in shutdown. FUNCTION MAX1566 (AUX2 is configured as a boost): FB2 feedback threshold is 1.25V. MAX1567 (AUX2 is configured as an inverter): FB2 feedback threshold is 0V.
31
FB2
32
INDL2
MAX1566 (AUX2 is configured as a boost): connect INDL2 to PVSU for Voltage Input for AUX2 optimum N-channel gate drive. Gate Driver. The voltage MAX1567 (AUX2 is configured as an inverter): connect INDL2 to the at INDL2 sets the high external P-channel MOSFET source to ensure the P channel is completely gate-drive voltage. off when DL2 swings high. Analog Ground. Connect to all PG_ pins as close to the IC as possible. AUX2 Controller GateDrive Output. DL2 drives between INDL2 and GND. The MAX1566 configures DL2 to drive an N-channel FET in a boost configuration. DL2 is driven low in shutdown, overload, and thermal limit. The MAX1567 configures DL2 to drive a PFET in an inverter configuration. DL2 is driven high in shutdown, overload, and thermal limit.
33
GND
34
DL2
35
DL3
AUX3 Controller Gate-Drive Output. Connect to the gate of an N-channel MOSFET. DL3 drives between GND and PVSU and supplies up to 500mA. This pin is actively driven to GND in shutdown, overload, and thermal limit. AUX1 Controller Gate-Drive Output. Connect to the gate of an N-channel MOSFET. DL1 drives between GND and PVSU and supplies up to 500mA. This pin is actively driven to GND in shutdown, overload, and thermal limit. IC Power Input. Connect PVSU and PV together. AUX3 Controller Compensation Node. Connect a series resistor-capacitor from this pin to GND for compensating the converter control loop. This pin is actively driven to GND in shutdown, overload, and thermal limit. See the AUX Compensation section. AUX3 Controller Current-Feedback Input. Connect a resistor from FB3L to GND to set LED current in LED boost-drive circuits. The feedback threshold is 0.2V. Connect this pin to GND if using only the FB3H feedback. This pin is high impedance in shutdown. AUX3 Controller On/Off Input. Logic high = on; however, turn-on is locked out until 1024 OSC cycles after the step-up has reached regulation. This pin has an internal 330k pulldown resistance to GND. Exposed Metal Pad. This pad is connected to ground. Note this internal connection is a soft-connect, meaning there is no internal metal or bond wire physically connecting the exposed pad to the GND pin. The connection is through the silicon substrate of the die and then through a conductive epoxy. Connecting the exposed pad to ground does not remove the requirement for a good ground connection to the appropriate pins.
36 37 38
DL1 PV CC3
39
FB3L
40
ON3
Pad
EP
14
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Six-Channel, High-Efficiency, Digital Camera Power Supplies
Detailed Description
The MAX1566/MAX1567 include the following blocks to build a multiple-output digital camera power-supply system. Both devices can accept inputs from a variety of sources including 1-cell Li+ batteries, 2-cell alkaline or NiMH batteries, and even systems designed to accept both battery types. The MAX1566/ MAX1567 include six DC-to-DC converter channels to generate all required voltages: * Step-up DC-to-DC converter (_SU pins) with on-chip power FETS * Main DC-to-DC converter (_M pins) with on-chip power FETS that can be configured as either a stepup or step-down DC-to-DC converter * Step-down core DC-to-DC converter with on-chip MOSFETs (_SD pins) * AUX1 DC-to-DC controller for boost and flyback converters * AUX2 DC-to-DC controller for boost and flyback converters (MAX1566) * AUX2 DC-to-DC controller for inverting DC-to-DC converters (MAX1567) * AUX3 DC-to-DC controller for white LED as well as conventional boost applications; includes open LED overvoltage protection
Main DC-to-DC Converter (Step-Up or Step-Down)
The main converter can be configured as a step-up (Figure 2) or a step-down converter (Figure 1) with the SUSD pin. The main DC-to-DC converter is typically used to generate 3.3V, but any voltage from 2.7V to 5V can be set; however, the main output must not be set higher than the step-up output (PVSU). An internal MOSFET switch and synchronous rectifier allow conversion efficiencies as high as 95%. Under moderate to heavy loading, the converter operates in a low-noise PWM mode with constant frequency and modulated pulse width. Switching harmonics generated by fixed-frequency operation are consistent and easily filtered. Efficiency is enhanced under light loading (<150mA typical for step-up mode, <100mA typical for step-down mode) by assuming an Idle Mode during which the converter switches only as needed to service the load. Step-down operation can be direct from a Li+ cell if the minimum input voltage exceeds the desired output by approximately 200mV. Note that if the main DC-to-DC, operating as a step-down, operates in dropout, the overload protection circuit senses an out-of-regulation condition and turns off all channels. Li+ to 3.3V Boost-Buck Operation When generating 3.3V from an Li+ cell, boost-buck operation may be needed so a regulated output can be maintained for input voltages above and below 3.3V. In that case, it may be best to configure the main converter as a step-down (SUSD = GND) and to connect its input, PVM, to the step-up output (PVSU), set to a voltage at or above 4.2V (Figures 1 and 3). The compound efficiency with this connection is typically up to 90%. This connection is also suitable for designs that must operate from both 1-cell Li+ and 2 AA cells. Note that the step-up output supplies both the step-up load and the main step-down input current when the main is powered from the step-up. The main input current reduces the available step-up output current for other loads. 2 AA to 3.3V Operation In designs that operate only from 2 AA cells, the main DC-to-DC can be configured as a boost converter (SUSD = PVM) to maximize the 3.3V efficiency (Figure 2).
MAX1566/MAX1567
Step-Up DC-to-DC Converter
The step-up DC-to-DC switching converter typically is used to generate a 5V output voltage from a 1.5V to 4.5V battery input, but any voltage from VIN to 5V can be set. An internal NFET switch and external synchronous rectifier allow conversion efficiencies as high as 95%. Under moderate to heavy loading, the converter operates in a low-noise PWM mode with constant frequency and modulated pulse width. Switching harmonics generated by fixed-frequency operation are consistent and easily filtered. Efficiency is enhanced under light (<75mA typ) loading by an Idle Mode that switches the step-up only as needed to service the load. In this mode, the maximum inductor current is 150mA for each pulse.
______________________________________________________________________________________
15
Six-Channel, High-Efficiency, Digital Camera Power Supplies MAX1566/MAX1567
VBATT 1 Li+ 2.8V TO 4.2V C15 10F C16 10F L2 1.2H DL1 D6 N2 FB1 DL3 INDL2 DL2 FB3H R2 90.9k AUX3 PWM FB3L AUX2 INVERTING PWM D7 R13 549k C17 1F P1 TO VBATT L3 22H -7.5V 40mA R11 1M
MAX1567
L1 1.4H C1 1F D1 N1 R1 1M OUTSU AUX1 PWM
OUTSU
C18 1F
15V 20mA R12 90.9k
D2-D5 LEDS
FB2 AUX1OK
TO REF R14 90.9k TO VBATT C10 47F VSU +5V 500mA
C2 0.1F R3 10 VSU R4 47k
REF PV PVSU OSC D8 LXSU L4 10H
C3 100pF ONSU ONM ONSD ON3 (LED) ON1 ON2 SUSD CCSU R5 R6 C4 R7 C5 R8 C6 R9 C7 R10 C8 C9 GND CC2 CC1 CC3 CCSD CCM
CURRENTMODE STEP-UP PWM
R15 274k
PGSU FBSU OK PWR ON OR FAULT PVM L5 10H C11 10F SCF
R16 90.9k
CURRENTMODE UP OR DOWN PWM
LXM
PGM FBM PVSD CURRENTMODE STEPDOWN PWM
R17 150k R18 90.9k
C12 22F
VM +3.3V 200mA
LXSD
L6 5.6H R19 40.2k
TO C13 BATT 10F VSD +1.8V 350mA
C14 22F
FBSD SDOK PGSD R20 90.9k
Figure 1. Typical 1-Cell Li+ Powered System (3.3V logic is stepped down from +5V, and 1.8V core is stepped down directly from the battery. Alternate connections are shown in the following figures.)
16
______________________________________________________________________________________
Six-Channel, High-Efficiency, Digital Camera Power Supplies MAX1566/MAX1567
VBATT 2 AA 1.5V TO 3.4V C15 10F C16 10F L2 1.2H
MAX1567
L1 1.4H C1 1F D1 N1 R1 1M DL3 OUTSU AUX1 PWM
OUTSU DL1 D6 N2 FB1 INDL2 DL2
C18 1F R11 1M
15V 20mA R12 90.9k
P1 D7
TO VSU L3 22H -7.5V 40mA
FB3H R2 90.9k AUX3 PWM FB3L AUX2 INVERTING PWM
D2-D5 LEDS
FB2 AUX1OK
R13 549k
C17 1F
TO REF R14 90.9k TO VBATT C10 47F VSU +5V 350mA
C2 0.1F R3 10 VSU R4 47k
REF PV PVSU OSC D8 LXSU L4 4.7H
C3 100pF ONSU ONM ONSD ON3 (LED) ON1 ON2 SUSD CCSU R5 R6 C4 R7 C5 R8 C6 R9 C7 R10 C8 C9 GND CC2 CC1 CC3 CCSD CCM
CURRENTMODE STEP-UP PWM
R15 274k
PGSU FBSU OK PWR ON OR FAULT PVM L5 3.3H C11 10F SCF TO VBATT
R16 90.9k
TO VSU
CURRENTMODE UP OR DOWN PWM
C21 47F R17 150k
VM +3.3V 500mA
LXM
C12 10F PGM FBM PVSD TO C13 VM 10F
R18 90.9k
CURRENTMODE STEPDOWN PWM
LXSD
L6 10H R19 40.2k
C14 47F
VSD +1.8V 250mA
FBSD SDOK PGSD R20 90.9k
Figure 2. Typical 2-Cell AA-Powered System (3.3V is boosted from the battery and 1.8V is stepped down from VM (3.3V).) ______________________________________________________________________________________ 17
Six-Channel, High-Efficiency, Digital Camera Power Supplies MAX1566/MAX1567
VBATT 2 AA OR Li+ 1.5V TO 4.2V C15 10F C16 10F L2 1.2H
MAX1567
L1 1.4H C1 1F D1 N1 R1 1M DL3 OUTSU AUX1 PWM
OUTSU DL1 D6 N2 FB1 INDL2 DL2
C18 1F R11 1M
15V 20mA R12 90.9k
P1 D7
TO VSU L3 22H -7.5V 40mA
FB3H R2 90.9k AUX3 PWM FB3L AUX2 INVERTING PWM
D2-D5 LEDS
FB2 AUX1OK
R13 549k
C17 1F
TO REF R14 90.9k TO VBATT C10 47F VSU +5V 100mA
C2 0.1F R3 10 VSU R4 47k
REF PV PVSU OSC D8 LXSU L4 4.7H
C3 100pF ONSU ONM ONSD ON3 (LED) ON1 ON2 SUSD CCSU R5 R6 C4 R7 C5 R8 C6 R9 C7 R10 C8 C9 GND CC2 CC1 CC3 CCSD CCM
CURRENTMODE STEP-UP PWM
R15 274k
PGSU FBSU OK PWR ON OR FAULT PVM L5 10H C11 10F SCF
R16 90.9k
CURRENTMODE UP OR DOWN PWM
LXM
PGM FBM PVSD CURRENTMODE STEPDOWN PWM
R17 150k R18 90.9k
C12 22F
VM +3.3V 200mA
LXSD
L6 10H R19 40.2k
TO C13 BATT 10F VSD +1.8V 200mA
C14 22F
FBSD SDOK PGSD R20 90.9k
Figure 3. Li+ or Multibattery Input (This power supply accepts inputs from 1.5V to 4.2V, so it can operate from either 2 AA cells or 1 Li+ cell. The 3.3V logic supply and the 1.8V core supply are both stepped down from 5V for true boost-buck operation.) 18 ______________________________________________________________________________________
Six-Channel, High-Efficiency, Digital Camera Power Supplies MAX1566/MAX1567
VSU 2.35V ONSU VREF 1V ONSU FLTALL 100,000CLOCK-CYCLE FAULT TIMER FAULT IN CLK PV OSC REF 300ns ONE-SHOT TO INTERNAL POWER REFOK INTERNAL POWEROK NORMAL MODE STARTUP OSCILLATOR
DIE OVER TEMP
MAX1566
1.25V REFERENCE
REF
GND
CCSU PVSU FBSU FAULT CURRENTMODE DC-TO-DC STEP-UP TO VREF LXSU
STEP-UP SOFT-START TIMER DONE (SUSSD)
SOFT-START RAMP GENERATOR
PGSU ONSU FLTALL
CCSD PVSD FBSD FAULT CURRENTMODE DC-TO-DC STEP-DOWN TO VREF LXSD
SOFT-START RAMP GENERATOR ONSD SUSSD FLTALL
PGND SDOK SUSD
PVM CC_ FB_ FAULT 1 OF 3 VOLTAGE-MODE DC-TO-DC CONTROLLERS AUX_ FAULT CURRENTMODE DC-TO-DC STEP-DOWN OR STEP-UP FLTALL SUSSD
LXM
SOFT-START RAMP GENERATOR ON_
TO VREF
PGM
FBM SUSSD FLTALL
DL_
TO VREF CLK
SOFT-START RAMP GENERATOR ONM AUX1OK
Figure 4. MAX1566 Functional Diagram ______________________________________________________________________________________ 19
Six-Channel, High-Efficiency, Digital Camera Power Supplies MAX1566/MAX1567
Core Step-Down DC-to-DC Converter
The step-down DC-to-DC is optimized for generating low output voltages (down to 1.25V) at high efficiency. The step-down runs from the voltage at PVSD. This pin can be connected directly to the battery if sufficient headroom exists to avoid dropout; otherwise, PVSD can be powered from the output of another converter. The stepdown can also operate with the step-up, or the main converter in step-up mode, for boost-buck operation. Under moderate to heavy loading, the converter operates in a low-noise PWM mode with constant frequency and modulated pulse width. Efficiency is enhanced under light (<75mA typ) loading by assuming an Idle Mode during which the step-down switches only as needed to service the load. In this mode, the maximum inductor current is 100mA for each pulse. The stepdown DC-to-DC is inactive until the step-up DC-to-DC is in regulation. The step-down also features an open-drain SDOK output that goes low when the step-down output is in regulation. SDOK can be used to drive an external MOSFET switch that gates 3.3V power to the processor after the core voltage is in regulation. This connection is shown in Figure 15. The auxiliary controllers do not start until 1024 OSC cycles after the step-up DC-to-DC output is in regulation. If the auxiliary controller remains faulted for 100,000 OSC cycles (200ms at 500kHz), then all MAX1566/MAX1567 channels latch off. Maximum Duty Cycle The AUX PWM controllers have a guaranteed maximum duty cycle of 80%: all controllers can achieve at least 80% and typically reach 85%. In boost designs that employ continuous current, the maximum duty cycle limits the boost ratio so: 1 - VIN / VOUT < 80% With discontinuous inductor current, no such limit exists for the input/output ratio since the inductor has time to fully discharge before the next cycle begins. AUX1 AUX1 can be used for conventional DC-to-DC boost and flyback designs (Figures 8 and 9). Its output (DL1) is designed to drive an N-channel MOSFET. Its feedback (FB1) threshold is 1.25V. AUX2 In the MAX1566, AUX2 is identical to AUX1. In the MAX1567, AUX2 is an inverting controller that generates a regulated negative output voltage, typically for CCD and LCD bias. This is useful in height-limited designs where transformers may not be desired. The AUX2 MOSFET driver (DL2) in the MAX1567 is designed to drive P-channel MOSFETs. INDL2 biases the driver so VINDL2 is the high output level of DL2. INDL2 should be connected to the P-channel MOSFET source to ensure the MOSFET turns completely off when DL2 is high. See Figure 10 for a typical inverter circuit. AUX3 DC-to-DC Controller, LED Driver The AUX3 step-up DC-to-DC controller has two feedback inputs, FB3L and FB3H, with feedback thresholds of 0.2V (FB3L) and 1.25V (FB3H). If used as a conventional voltage-output step-up, FB3L is grounded and FB3H is used as the feedback input. In that case, AUX3 behaves exactly like AUX1. If AUX3 is used as a switch-mode boost current source for white LEDs, FB3L provides current-sensing feedback, while FB3H provides (optional) open-LED overvoltage protection (Figure 7).
AUX1, AUX2, and AUX3 DC-to-DC Controllers
The three auxiliary controllers operate as fixed-frequency voltage-mode PWM controllers. They do not have internal MOSFETs, so output power is determined by external components. The controllers regulate output voltage by modulating the pulse width of the DL_ drive signal to an external MOSFET switch. On the MAX1566, AUX1 and AUX2 are boost/flyback PWM controllers. On the MAX1567, AUX1 is a boost/flyback PWM controller, but AUX2 is an inverting PWM controller. On both devices, AUX3 is a boost/flyback controller that can be connected to regulate output voltage and/or current (for white-LED drive). Figure 5 shows a functional diagram of an AUX boost controller channel. A sawtooth oscillator signal at OSC governs timing. At the start of each cycle, DL_ goes high, turning on the external NFET switch. The switch then turns off when the internally level-shifted sawtooth rises above CC_ or when the maximum duty cycle is exceeded. The switch remains off until the start of the next cycle. A transconductance error amplifier forms an integrator at CC_ to maintain high DC loop gain and accuracy.
20
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Six-Channel, High-Efficiency, Digital Camera Power Supplies MAX1566/MAX1567
FB2
CC2 R LEVEL SHIFT REFI SOFT-START REF 0.85 REF S Q DL_
MAX1567 AUX2 INVERTER
CLK
OSC
FAULT PROTECTION ENABLE
FB
CC R LEVEL SHIFT REFI SOFT-START REF 0.85 REF S Q DL_
MAX1566/MAX1567 AUX_ BOOST
CLK
OSC
FAULT PROTECTION ENABLE
IN 1024 CLOCK CYCLES, SOFT-START RAMPS UP REFI FROM 0V TO VREF IN MAX1566/MAX1567 AUX_ BOOST CONTROLLERS AND RAMPS DOWN REFI FROM VREF TO 0V IN MAX1567 AUX2 INVERTER.
Figure 5. AUX Controller Functional Diagram ______________________________________________________________________________________ 21
Six-Channel, High-Efficiency, Digital Camera Power Supplies MAX1566/MAX1567
VSU
ROSC OSC COSC VREF (1.25V) 150ns ONE-SHOT
MAX1566 MAX1567 (PARTIAL)
AUX PWM PVSU DL_
TO VBATT
Q1
D6
+15V 50mA LCD
FB_ MAX1566 MAX1567
NOTE: THIS CIRCUIT CAN OPERATE WITH AUX1, AUX2, OR AUX3 ON THE MAX1566, AND WITH AUX1 OR AUX3 ON THE MAX1567. TO USE AUX3, FB3L = GND, AND FB3H IS USED FOR FEEDBACK.
Figure 6. Oscillator Functional Diagram
TO VBATT
Figure 8. +15V LCD Bias with Basic Boost Topology
TO VBATT +15V 50mA CCD+
MAX1566 MAX1567 (PARTIAL)
PVSU DL3 R1 FB3H (1.25V) AUX3 PWM R2 FB3L (0.2V)
MAX1566 MAX1567 (PARTIAL)
AUX PWM PVSU DL_
Q1
D2 -7.5V 30mA CCD-
D2-D5 LEDS
FB_ NOTE: THIS CIRCUIT CAN OPERATE WITH AUX1, AUX2, OR AUX3 ON THE MAX1566, AND WITH AUX1 OR AUX3 ON THE MAX1567. TO USE AUX3, FB3L = GND, AND FB3H IS USED FOR FEEDBACK.
R3
NOTE: IF OPEN LED PROTECTION IS NOT REQUIRED, REMOVE R2 AND R3 AND GROUND FB3H.
Figure 7. LED drive with open LED overvoltage protection is provided by the additional feedback input to AUX3, FB3H.
Figure 9. +15V and -7.5V CCD Bias with Transformer
Master-Slave Configurations
The MAX1566/MAX1567 support MAX1801 slave PWM controllers that obtain input power, a voltage reference, and an oscillator signal directly from the MAX1566/ MAX1567 master. The master-slave configuration allows channels to be easily added and minimizes system cost by eliminating redundant circuitry. The slaves also control the harmonic content of noise because their operating frequency is synchronized to that of the MAX1566/
22
MAX1567 master converter. A MAX1801 connection to the MAX1566/MAX1567 is shown in Figure 14.
Status Outputs (SDOK, AUX1OK, SCF)
The MAX1566/MAX1567 include three versatile status outputs that can provide information to the system. All are open-drain outputs and can directly drive MOSFET switches to facilitate sequencing, disconnect loads during overloads, or perform other hardware-based functions.
______________________________________________________________________________________
Six-Channel, High-Efficiency, Digital Camera Power Supplies MAX1566/MAX1567
MAX1567 (PARTIAL)
INDL2 DL2 AUX_ PWM -7.5V 100mA AUX2 INVERTING PWM RTOP FB2 RREF REF DL_ PVSU -7.5V 20mA FB_ TO VBATT TO VBATT +15V 20mA
MAX1566/MAX1567 (PARTIAL)
Figure 10. Regulated -7.5V Negative CCD (Bias is provided by conventional inverter (works only with the MAX1567).)
IN L1 10H TO VBATT 1F D2 C2 1F VOUT+ +15V 20mA R1 1M FB_ +1.25V PVSU Q1 DL_ C1 1F D1 R2 90.9k D3 VOUT-15V C3 10mA 1F SHDN GND
OUT
AUX_ PWM
FB_
MAX1616
NOTE: THIS CIRCUIT CAN OPERATE WITH AUX1, AUX2, OR AUX3 ON THE MAX1566, AND WITH AUX1 OR AUX3 ON THE MAX1567. TO USE AUX3, FB3L = GND, AND FB3H IS USED FOR FEEDBACK.
MAX1566 MAX1567 (PARTIAL)
Figure 11. 15V Output Using an AUX-Driven Boost with Charge-Pump Inversion
Figure 12. +15V and -7.5V CCD Bias Without Transformer Using Boost with a Diode-Capacitor Charge Pump (A positiveoutput linear regulator (MAX1616) can be used to regulate the negative output of the charge pump.)
SDOK pulls low when the step-down has successfully completed soft-start. SDOK goes high impedance in shutdown, overload, and thermal limit. A typical use for SDOK is to drive a P-channel MOSFET that connects 3.3V power to the CPU I/O after the CPU core is powered up (Figure 15), thus providing safe sequencing in hardware without system intervention. AUX1OK pulls low when the AUX1 controller has successfully completed soft-start. AUX1OK goes high impedance in shutdown, overload, and thermal limit. A typical use for AUX1OK is to drive a P-channel MOSFET
that connects 5V power to the CCD after the 15V CCD bias (generated by AUX1) is powered up (Figure 16). SCF goes high (high impedance, open drain) when overload protection occurs. Under normal operation, SCF pulls low. SCF can drive a high-side P-channel MOSFET switch that can disconnect a load during power-up or when a channel turns off in response to a logic command or an overload. Several connections are possible for SCF. One is shown in Figure 17 where SCF provides load disconnect for the step-up on fault and power-up.
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Six-Channel, High-Efficiency, Digital Camera Power Supplies MAX1566/MAX1567
INPUT 1-CELL Li+ VSU L1 PV PVSU DL_ PART OF MAX1566 MAX1567 (PARTIAL) C2 Q1 FB_ R2 R1
FB COMP GND REF DCON REF TO BATT
L2 D1 OUTPUT 3.3V
VOUT DL IN
PVSU
MAX1801 OSC
OSC
MAX1566 MAX1567 (PARTIAL)
Figure 13. SEPIC Converter Additional Boost-Buck Channel
Figure 14. Adding a PWM Channel with an External MAX1801 Slave Controller
MAX1566 MAX1567 (PARTIAL)
PVM
SUSD
CURRENTMODE UP OR DOWN PWM
LXM
L3
VM +3.3V
PGM FBM SDOK
3.3V TO CPU
PVSD
TO VBATT
CURRENTMODE STEPDOWN PWM
LXSD
L4
VSD +1.8V 350mA
FBSD PGSD
Figure 15. Using SDOK to Drive External PFET that Gates 3.3V Power to CPU After 1.8V Core Voltage Is in Regulation 24 ______________________________________________________________________________________
Six-Channel, High-Efficiency, Digital Camera Power Supplies MAX1566/MAX1567
TO VBATT
MAX1566 MAX1567 (PARTIAL)
PVSU AUX1 PWM DL1 D6 15V 100mA
FB1 AUX1OK
PV PVSU TO VBATT CURRENTMODE STEP-UP PWM LXSU L2
GATED +5V TO CCD VSU +5V
PGSU
FBSU
Figure 16. AUX1OK Drives an External PFET that Gates 5V Supply to the CCD After the +15V CCD Bias Supply Is Up
Soft-Start
The MAX1566/MAX1567 channels feature a soft-start function that limits inrush current and prevents excessive battery loading at startup by ramping the output voltage of each channel up to the regulation voltage. This is accomplished by ramping the internal reference inputs to each channel error amplifier from 0V to the 1.25V reference voltage over a period of 4096 oscillator cycles (16ms at 500kHz) when initial power is applied or when a channel is enabled. The step-down soft-start ramp takes half the time (2048 clock cycles) of the other channel ramps. This allows the step-down and main outputs to track each other and rise at nearly the same dV/dt rate on power-up. Once the step-down output reaches its regulation point (1.5V or 1.8V typ), the main output (3.3V typ) continues to rise at the same ramp rate. See the Typical Operating Characteristics Main and Step-Down Startup Waveforms graphs.
Soft-start is not included in the step-up converter to avoid limiting startup capability with loading.
Fault Protection
The MAX1566/MAX1567 have robust fault and overload protection. After power-up, the device is set to detect an out-of-regulation state that could be caused by an overload or short. If any DC-to-DC converter channel (step-up, main, step-down, or any of the auxiliary controllers) remains faulted for 100,000 clock cycles (200ms at 500kHz), then all outputs latch off until the step-up DC-to-DC converter is reinitialized by the ONSU pin or by cycling the input power. The faultdetection circuitry for any channel is disabled during its initial turn-on soft-start sequence. An exception to the standard fault behavior is that there is no 100,000 clock cycle delay in entering the fault state if the step-up output (PVSU) is dragged below its 2.5V UVLO threshold or is shorted. In this case, the
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Six-Channel, High-Efficiency, Digital Camera Power Supplies MAX1566/MAX1567
step-up UVLO immediately triggers and shuts down all channels. The step-up then continues to attempt starting. If the step-up output short remains, these attempts cannot succeed since PVSU remains near ground. If a soft-short or overload remains on PVSU, the startup oscillator switches the internal N-channel MOSFET, but fault is retriggered if regulation is not achieved by the end of the soft-start interval. If PVSU is dragged below the input, the overload is supplied by the body diode of the internal synchronous rectifier, or by a Schottky diode connected from the battery to PVSU. If desired, this overload current can be interrupted by a P-channel MOSFET controlled by SCF, as shown in Figure 17.
MAX1566 MAX1567 (PARTIAL)
PV PVSU TO VBATT VSU +5V
CURRENT-MODE STEP-UP PWM
LXSU
L2
PGSU FBSD SCF
Reference
The MAX1566/MAX1567 has a precise 1.250V reference. Connect a 0.1F ceramic bypass capacitor from REF to GND within 0.2in (5mm) of the REF pin. REF can source up to 200A and is enabled whenever ONSU is high and PVSU is above 2.5V. The auxiliary controllers and MAX1801 slave controllers (if connected) each sink up to 30A REF current during startup. In addition, the feedback network for the AUX2 inverter (MAX1567) also draws current from REF. If the 200A REF load limit must be exceeded, buffer REF with an external op amp.
OK PWR ON OR FAULT
Figure 17. SCF Drives PFET Load Switch on 5V to Disconnect Load on Fault and Allow Full-Load Startup
VSU 3.3V
PVSU PV
Oscillator
All DC-to-DC converter channels employ fixed-frequency PWM operation. The operating frequency is set by an RC network at the OSC pin. The range of usable settings is 100kHz to 1MHz. When MAX1801 slave controllers are added, they operate at the frequency set by OSC. The oscillator uses a comparator, a 150ns one-shot, and an internal NFET switch in conjunction with an external timing resistor and capacitor (Figure 6). When the switch is open, the capacitor voltage exponentially approaches the step-up output voltage from zero with a time constant given by the product of ROSC and COSC. The comparator output switches high when the capacitor voltage reaches VREF (1.25V). In turn, the one-shot activates the internal MOSFET switch to discharge the capacitor for 150ns, and the cycle repeats. The oscillation frequency changes as the main output voltage ramps upward following startup. The oscillation frequency is then constant once the main output is in regulation.
MAX1566 MAX1567 (PARTIAL)
PVSD 10F
CURRENT-MODE STEP-DOWN
LXSD
4.7H 22F
VSD 0.8V
PGSD FBSD R3 100k VFBSD 1.25V R1 56k
R2 100k
Figure 18. Setting PVSD for Outputs Below 1.25V
Low-Voltage Startup Oscillator
The MAX1566/MAX1567 internal control and referencevoltage circuitry receive power from PVSU and do not function when PVSU is less than 2.5V. To ensure lowvoltage startup, the step-up employs a low-voltage startup oscillator that activates at 0.9V if a Schottky rectifier is connected from VBATT to PVSU (1.1V with no
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Schottky rectifier). The startup oscillator drives the internal N-channel MOSFET at LXSU until PVSU reaches 2.5V, at which point voltage control is passed to the current-mode PWM circuitry. Once in regulation, the MAX1566/MAX1567 operate with inputs as low as 0.7V since internal power for the IC is supplied by PVSU. At low input voltages, the step-
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Six-Channel, High-Efficiency, Digital Camera Power Supplies
up may have difficulty starting into heavy loads (see the Minimum Startup Voltage vs. Load Current (OUTSU) graph in the Typical Operating Characteristics); however, this can be remedied by connecting an external Pchannel load switch driven by SCF so the load is not connected until the PVSU is in regulation (Figure 17). RTOP = RBOTTOM[(VOUT / 1.25) - 1] When using AUX3 to drive white LEDs (Figure 7), select the LED current-setting resistor (R3, Figure 7) using the following formula: R3 = 0.2V / ILED The FB2 threshold on the MAX1567 is 0V. To set the AUX2 negative output voltage, connect a resistive voltage-divider from the negative output to the FB2 input, and then to REF. The FB2 input bias current is less than 100nA, so choose the REF-side (FB2-to-REF) resistor (RREF) to be 100k or less. Then calculate the top-side (output-to-FB2) resistor: RTOP = RREF(-VOUT(AUX2) / 1.25)
MAX1566/MAX1567
Shutdown
The step-up converter is activated with a high input at ONSU. The main converter (step-up or step-down) is activated by a high input on ONM. The step-down and auxiliary DC-to-DC converters 1, 2, and 3 activate with high inputs at ONSD, ON1, ON2, and ON3, respectively. The step-down, main, and AUX_ converters cannot be activated until PVSU is in regulation. For automatic startup, connect ON_ to PVSU or a logic level greater than 1.6V.
General Filter Capacitor Selection
The input capacitor in a DC-to-DC converter reduces current peaks drawn from the battery or other input power source and reduces switching noise in the controller. The impedance of the input capacitor at the switching frequency should be less than that of the input source so high-frequency switching currents do not pass through the input source. The output capacitor keeps output ripple small and ensures control-loop stability. The output capacitor must also have low impedance at the switching frequency. Ceramic, polymer, and tantalum capacitors are suitable, with ceramic exhibiting the lowest ESR and high-frequency impedance. Output ripple with a ceramic output capacitor is approximately as follows: VRIPPLE = IL(PEAK)[1 / (2 x fOSC x COUT)] If the capacitor has significant ESR, the output ripple component due to capacitor ESR is as follows: VRIPPLE(ESR) = IL(PEAK) x ESR Output capacitor specifics are also discussed in each converter's Compensation section.
Design Procedure
Setting the Switching Frequency
Choose a switching frequency to optimize external component size or circuit efficiency for the particular application. Typically, switching frequencies between 400kHz and 500kHz offer a good balance between component size and circuit efficiency--higher frequencies generally allow smaller components, and lower frequencies give better conversion efficiency. The switching frequency is set with an external timing resistor (ROSC) and capacitor (COSC). At the beginning of a cycle, the timing capacitor charges through the resistor until it reaches VREF. The charge time, t1, is as follows: t1 = -ROSC x COSC x In(1 - 1.25 / VPVSU) The capacitor voltage then decays to zero over time, t2 = 150ns. The oscillator frequency is as follows: fOSC = 1 / (t1 + t2) fOSC can be set from 100kHz to 1MHz. Choose COSC between 22pF and 470pF. Determine ROSC: ROSC = (150ns - 1 / fOSC) / (COSC ln[1 - 1.25 / VPVSU]) See the Typical Operating Characteristics for fOSC vs. ROSC using different values of COSC.
Step-Up Component Selection
This section describes component selection for the step-up, as well as for the main, if SUSD = PV. The external components required for the step-up are an inductor, an input and output filter capacitor, and a compensation RC. The inductor is typically selected to operate with continuous current for best efficiency. An exception might be if the step-up ratio, (VOUT / VIN), is greater than 1 / (1 DMAX), where DMAX is the maximum PWM duty factor of 80%. When using the step-up channel to boost from a low input voltage, loaded startup is aided by connecting a
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Setting Output Voltages
All MAX1566/MAX1567 output voltages are resistor set. The FB_ threshold is 1.25V for all channels except for FB3L (0.2V) on both devices and FB2 (inverter) on the MAX1567. When setting the voltage for any channel except the MAX1567 AUX2, connect a resistive voltage-divider from the channel output to the corresponding FB_ input and then to GND. The FB_ input bias current is less than 100nA, so choose the bottom-side (FB_-to-GND) resistor to be 100k or less. Then calculate the top-side (output-to-FB_) resistor:
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Six-Channel, High-Efficiency, Digital Camera Power Supplies MAX1566/MAX1567
Schottky diode from the battery to PVSU. See the Minimum Startup Voltage vs. Load Current graph in the Typical Operating Characteristics. Step-Up Inductor In most step-up designs, a reasonable inductor value (LIDEAL) can be derived from the following equation, which sets continuous peak-to-peak inductor current at 1/2 the DC inductor current: LIDEAL = [2VIN(MAX) x D(1 - D)] / (IOUT x fOSC) where D is the duty factor given by: D = 1 - (VIN / VOUT) Given LIDEAL, the consistent peak-to-peak inductor current is 0.5 IOUT / (1 - D). The peak inductor current, IIND(PK) = 1.25 IOUT / (1 - D). Inductance values smaller than LIDEAL can be used to reduce inductor size; however, if much smaller values are used, inductor current rises and a larger output capacitance may be required to suppress output ripple. Step-Up Compensation The inductor and output capacitor are usually chosen first in consideration of performance, size, and cost. The compensation resistor and capacitor are then chosen to optimize control-loop stability. In some cases, it may help to readjust the inductor or output-capacitor value to get optimum results. For typical designs, the component values in the circuit of Figure 1 yield good results. The step-up converter employs current-mode control, thereby simplifying the control-loop compensation. When the converter operates with continuous inductor current (typically the case), a right-half-plane zero appears in the loop-gain frequency response. To ensure stability, the control-loop gain should cross over (drop below unity gain) at a frequency (fC) much less than that of the right-half-plane zero. The relevant characteristics for step-up channel compensation are as follows: * Transconductance (from FB to CC), gmEA (135S) * Current-sense amplifier transresistance, R CS (0.3V/A) * Feedback regulation voltage, VFB (1.25V) * Step-up output voltage, VSU, in V * Output load equivalent resistance, RLOAD, in = VOUT / ILOAD The key steps for step-up compensation are as follows: 1) Place fC sufficiently below the right-half-plane zero (RHPZ) and calculate CC. 2) Select RC based on the allowed load-step transient. RC sets a voltage delta on the CC pin that corresponds to load-current step. 3) Calculate the output-filter capacitor (COUT) required to allow the RC and CC selected. 4) Determine if C P is required (if calculated to be >10pF). For continuous conduction, the right-half-plane zero frequency (fRHPZ) is given by the following: fRHPZ = VOUT(1 - D)2 / (2 x L x ILOAD) where D = the duty cycle = 1 - (VIN / VOUT), L is the inductor value, and ILOAD is the maximum output current. Typically target crossover (fC) for 1/6 of the RHPZ. For example, if we assume fOSC = 500kHz, VIN = 2.5V, VOUT = 5V, and IOUT = 0.5A, then RLOAD = 10. If we select L = 4.7H, then: fRHPZ = 5 (2.5 / 5)2 / (2 x 4.7 x 10-6 x 0.5) = 84.65kHz Choose fC = 14kHz. Calculate CC: CC = (VFB / VOUT)(RLOAD / RCS)(gm / 2 x fC)(1 - D) = (1.25 / 5)(10 / 0.3) x [135S / (6.28 x 14kHz)] (2/5) = 6.4nF Choose 6.8nF. Now select R C so transient-droop requirements are met. As an example, if 4% transient droop is allowed, the input to the error amplifier moves 0.04 x 1.25V, or 50mV. The error-amp output drives 50mV x 135S, or 6.75A, across RC to provide transient gain. Since the current-sense transresistance is 0.3V/A, the value of RC that allows the required load-step swing is as follows: RC = 0.3 IIND(PK) / 6.75A In a step-up DC-to-DC converter, if LIDEAL is used, output current relates to inductor current by: IIND(PK) = 1.25 IOUT / (1 - D) = 1.25 IOUT x VOUT / VIN So, for a 500mA output load step with VIN = 2.5V and VOUT = 5V: RC = [1.25(0.3 x 0.5 x 5) / 2)] / 6.75A = 69.4k Note that the inductor does not limit the response in this case since it can ramp at 2.5V / 4.7H, or 530mA/s. The output filter capacitor is then chosen so the COUT RLOAD pole cancels the RC CC zero: COUT x RLOAD = RC x CC For the example: COUT = 68k x 6.8nF / 10 = 46F Choose 47F for COUT. If the available COUT is substantially different from the calculated value, insert the available C OUT value into the above equation and
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Six-Channel, High-Efficiency, Digital Camera Power Supplies
recalculate RC. Higher substituted COUT values allow a higher RC, which provides higher transient gain and consequently less transient droop. If the output filter capacitor has significant ESR, a zero occurs at the following: ZESR = 1 / (2 x COUT x RESR) If ZESR > fC, it can be ignored, as is typically the case with ceramic output capacitors. If ZESR is less than fC, it should be cancelled with a pole set by capacitor CP connected from CC to GND: CP = COUT x RESR / RC If CP is calculated to be <10pF, it can be omitted. * Output-load equivalent resistance, RLOAD, in = VOUT / ILOAD The key steps for step-down compensation are as follows: 1) Set the compensation RC to zero to cancel the RLOAD COUT pole. 2) Set the loop crossover below the lower of 1/5 the slope compensation pole or 1/5 the switching frequency. If we assume VIN = 2.5V, VOUT = 1.8V, and IOUT = 350mA, then RLOAD = 5.14. If we select fOSC = 500kHz and L = 5.6H. PSLOPE = VIN / (L) = 142kHz, so choose fC = 24kHz and calculate CC: CC = (VFB / VOUT)(RLOAD / RCS)(gm / 2 x fC) = (1.25 / 1.8)(5.14 / 0.6) x [135S / (6.28 x 24kHz)] = 6.4nF Choose 6.8nF. Now select R C so transient-droop requirements are met. As an example, if 4% transient droop is allowed, the input to the error amplifier moves 0.04 x 1.25V, or 50mV. The error-amp output drives 50mV x 135S, or 6.75A across RC to provide transient gain. Since the current-sense transresistance is 0.6V/A, the value of RC that allows the required load-step swing is as follows: RC = 0.6 IIND(PK) / 6.75A In a step-down DC-to-DC converter, if LIDEAL is used, output current relates to inductor current by the following: IIND(PK) = 1.25 IOUT So for a 250mA output load step with VIN = 2.5V and VOUT = 1.8V: RC = (1.25 x 0.6 x 0.25) / 6.75A = 27.8k Choose 27k. Note that the inductor does somewhat limit the response in this case since it ramps at (VIN - VOUT) / 5.6H, or (2.5 - 1.8) / 5.6H = 125mA/s. The output filter capacitor is then chosen so the COUT RLOAD pole cancels the RC CC zero: COUT x RLOAD = RC x CC For the example: COUT = 27k x 6.8nF / 5.14 = 35.7F Since ceramic capacitors are common in either 22F or 47F values, 22F is within a factor of two of the ideal value and still provides adequate phase margin for stability.
MAX1566/MAX1567
Step-Down Component Selection
This section describes component selection for the step-down converter, and for the main converter if used in step-down mode (SUSD = GND). Step-Down Inductor The external components required for the step-down are an inductor, input and output filter capacitors, and compensation RC network. The MAX1566/MAX1567 step-down converter provides best efficiency with continuous inductor current. A reasonable inductor value (LIDEAL) can be derived from the following: LIDEAL = [2(VIN) x D(1 - D)] / IOUT x fOSC This sets the peak-to-peak inductor current at 1/2 the DC inductor current. D is the duty cycle: D = VOUT / VIN Given LIDEAL, the peak-to-peak inductor current is 0.5 IOUT. The absolute-peak inductor current is 1.25 IOUT. Inductance values smaller than LIDEAL can be used to reduce inductor size; however, if much smaller values are used, inductor current rises, and a larger output capacitance may be required to suppress output ripple. Larger values than LIDEAL can be used to obtain higher output current, but typically with larger inductor size. Step-Down Compensation The relevant characteristics for step-down compensation are as follows: * Transconductance (from FB to CC), gmEA (135S) * Step-down slope-compensation pole, PSLOPE = VIN / (L) * Current-sense amplifier transresistance, R CS (0.6V/A) * Feedback-regulation voltage, VFB (1.25V) * Step-down output voltage, VSD, in V
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Six-Channel, High-Efficiency, Digital Camera Power Supplies MAX1566/MAX1567
If the output filter capacitor has significant ESR, a zero occurs at the following: ZESR = 1 / (2 x COUT x RESR) If ZESR > fC, it can be ignored, as is typically the case with ceramic output capacitors. If ZESR < fC, it should be cancelled with a pole set by capacitor CP connected from CC to GND: CP = COUT x RESR / RC If CP is calculated to be <10pF, it can be omitted. Diode For most AUX applications, a Schottky diode rectifies the output voltage. Schottky low forward voltage and fast recovery time provide the best performance in most applications. Silicon signal diodes (such as 1N4148) are sometimes adequate in low-current (<10mA), high-voltage (>10V) output circuits where the output voltage is large compared to the diode forward voltage. AUX Compensation The auxiliary controllers employ voltage-mode control to regulate their output voltage. Optimum compensation depends on whether the design uses continuous or discontinuous inductor current. AUX Step-Up, Discontinuous Inductor Current When the inductor current falls to zero on each switching cycle, it is described as discontinuous. The inductor is not utilized as efficiently as with continuous current, but in light-load applications this often has little negative impact since the coil losses may already be low compared to other losses. A benefit of discontinuous inductor current is more flexible loop compensation, and no maximum duty-cycle restriction on boost ratio. To ensure discontinuous operation, the inductor must have a sufficiently low inductance to fully discharge on each cycle. This occurs when: L < [VIN2 (VOUT - VIN) / VOUT3] [RLOAD / (2fOSC)] A discontinuous current boost has a single pole at the following: fP = (2VOUT - VIN) / (2 x RLOAD x COUT x VOUT) Choose the integrator cap so the unity-gain crossover, fC, occurs at fOSC / 10 or lower. Note that for many AUX circuits, such as those powering motors, LEDs, or other loads that do not require fast transient response, it is often acceptable to overcompensate by setting fC at fOSC / 20 or lower. CC is then determined by the following: CC = [2VOUT x VIN / ((2VOUT - VIN) x VRAMP)] [VOUT / (K(VOUT - VIN))]1/2 [(VFB / VOUT)(gM / (2 x fC))] where: K = 2L x fOSC / RLOAD and VRAMP is the internal slope-compensation voltage ramp of 1.25V.
AUX Controller Component Selection
External MOSFET All MAX1566/MAX1567 AUX controllers drive external logic-level MOSFETs. Significant MOSFET selection parameters are as follows: * On-resistance (RDS(ON)) * Maximum drain-to-source voltage (VDS(MAX)) * Total gate charge (QG) * Reverse transfer capacitance (CRSS) On the MAX1566, all AUX drivers are designed for Nchannel MOSFETs. On the MAX1567, AUX2 is a DC-toDC inverter, so DL2 is designed to drive a P-channel MOSFET. In both devices, the driver outputs DL1 and DL3 swing between PVSU and GND. MOSFET driver DL2 swings between INDL2 and GND. Use a MOSFET with on-resistance specified with gate drive at or below the main output voltage. The gate charge, QG, includes all capacitance associated with charging the gate and helps to predict MOSFET transition time between on and off states. MOSFET power dissipation is a combination of on-resistance and transition losses. The on-resistance loss is as follows: PRDSON = D x IL2 x RDS(ON) where D is the duty cycle, IL is the average inductor current, and RDS(ON) is MOSFET on-resistance. The transition loss is approximately as follows: PTRANS = (VOUT x IL x fOSC x tT) / 3 where VOUT is the output voltage, IL is the average inductor current, fOSC is the switching frequency, and tT is the transition time. The transition time is approximately QG / IG, where QG is the total gate charge, and IG is the gate-drive current (0.5A typ). The total power dissipation in the MOSFET is as follows: PMOSFET = PRDSON + PTRANS
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Six-Channel, High-Efficiency, Digital Camera Power Supplies
The CC RC zero is then used to cancel the fP pole, so: RC = RLOAD x COUT x VOUT / [(2VOUT - VIN) x CC] AUX Step-Up, Continuous Inductor Current Continuous inductor current can sometimes improve boost efficiency by lowering the ratio between peak inductor current and output current. It does this at the expense of a larger inductance value that requires larger size for a given current rating. With continuous inductorcurrent boost operation, there is a right-half-plane zero, ZRHP, at the following: ZRHP = (1 - D)2 x RLOAD / (2 x L) where (1 - D) = VIN / VOUT (in a boost converter). There is a complex pole pair at the following: f0 = VOUT / [2 x VIN (L x COUT)1/2] If the zero due to the output capacitance and ESR is less than 1/10 the right-half-plane zero: ZCOUT = 1 / (2 x COUT x RESR) < ZRHP / 10 Then choose CC so the crossover frequency fC occurs at ZCOUT. The ESR zero provides a phase boost at crossover: CC = (VIN / VRAMP) (VFB / VOUT) [gM / (2 x ZCOUT)] Choose RC to place the integrator zero, 1 / (2 x RC x CC), at f0 to cancel one of the pole pairs: RC = VIN(L x COUT)1/2 / (VOUT x CC) If ZCOUT is not less than ZRHP / 10 (as is typical with ceramic output capacitors) and continuous conduction is required, then cross the loop over before ZRHP and f0: fC < f0 / 10, and fC < ZRHP / 10 In that case: CC = (VIN / VRAMP) (VFB / VOUT) (gM / (2 x fC)) Place: 1 / (2 x RC x CC) = 1 / (2 x RLOAD x COUT), so that RC = RLOAD x COUT / CC Or, reduce the inductor value for discontinuous operation. MAX1567 AUX2 Inverter Compensation, Discontinuous Inductor Current If the load current is very low (40mA), discontinuous current is preferred for simple loop compensation and freedom from duty-cycle restrictions on the inverter input-output ratio. To ensure discontinuous operation, the inductor must have a sufficiently low inductance to fully discharge on each cycle. This occurs when: L < [VIN / (|VOUT| + VIN)]2 RLOAD / (2fOSC) A discontinuous current inverter has a single pole at the following: fP = 2 / (2 x RLOAD x COUT) Choose the integrator cap so the unity-gain crossover, fC, occurs at fOSC / 10 or lower. Note that for many AUX circuits that do not require fast transient response, it is often acceptable to overcompensate by setting fC at fOSC / 20 or lower. CC is then determined by the following: CC = [VIN / (K1/2 x VRAMP] [VREF / (VOUT + VREF)] [gM / (2 x fC)] where K = 2L x fOSC / RLOAD, and VRAMP is the internal slope-compensation voltage ramp of 1.25V. The CC RC zero is then used to cancel the fP pole, so: RC = (RLOAD x COUT) / (2CC) MAX1567 AUX2 Inverter Compensation, Continuous Inductor Current Continuous inductor current may be more suitable for larger load currents (50mA or more). It improves efficiency by lowering the ratio between peak inductor current and output current. It does this at the expense of a larger inductance value that requires larger size for a given current rating. With continuous inductor-current inverter operation, there is a right-half-plane zero, ZRHP, at: ZRHP = [(1 - D)2 / D] x RLOAD / (2 x L) where D = |VOUT| / (|VOUT| + VIN) (in an inverter). There is a complex pole pair at: f0 = (1 - D) / (2(L x C)1/2) If the zero due to the output-capacitor capacitance and ESR is less than 1/10 the right-half-plane zero: ZCOUT = 1 / (2 x COUT x RESR) < ZRHP / 10 Then choose CC such that the crossover frequency fC occurs at ZCOUT. The ESR zero provides a phase boost at crossover: CC = (VIN / VRAMP) [VREF / (VREF + |VOUT|)] [gM / (2 x ZCOUT)] Choose RC to place the integrator zero, 1 / (2 x RC x CC), at f0 to cancel one of the pole pairs: RC = (L x COUT)1/2 / [(1 - D) x CC] If ZCOUT is not less than ZRHP / 10 (as is typical with ceramic output capacitors) and continuous conduction is required, then cross the loop over before ZRHP and f0: fC < f0 /10, and fC < ZRHP / 10
MAX1566/MAX1567
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Six-Channel, High-Efficiency, Digital Camera Power Supplies MAX1566/MAX1567
In that case: CC = (VIN / VRAMP) [VREF / (VREF + |VOUT|)] [gM / (2 x fC)] Place: 1 / (2 x RC x CC) = 1 / (2 x RLOAD x COUT), so that RC = RLOAD x COUT / CC Or, reduce the inductor value for discontinuous operation. Furthermore, the cascaded boost-buck efficiency compares favorably with other boost-buck techniques.
LED, LCD, and Other Boost Applications
Any AUX channel (except for the AUX2 inverter on the MAX1567) can be used for a wide variety of step-up applications. These include generating 5V or some other voltage for motor or actuator drive, generating 15V or a similar voltage for LCD bias, or generating a step-up current source to efficiently drive a series array of white LEDs to display backlighting. Figures 7 and 8 show examples of these applications.
Applications Information
Typical Operating Circuits
Figures 1, 2, and 3 show connections for AA and Li+ battery arrangements. Figures 7-13 show various connections for the AUX1, 2, and 3 controllers. Figures 15, 16, and 17 show various connections for the SDOK, AUX1OK, and SCF outputs. Figure 1. Typical Operating Circuit for One Li+ Cell In this connection, the main converter is operated as a step-down (SUSD = GND) and is powered from PVSU. This provides boost-buck operation for the main 3.3V output so a regulated output is maintained over the Li+ 2.7V to 4.2V cell voltage range. The compound efficiency from the battery to the 3.3V output reaches 90%. The step-down 1.8V (core) output is powered directly from VBATT. The CCD and LCD voltages are generated with a transformerless design. AUX1 generates +15V for CCD positive and LCD bias. The MAX1567 AUX2 inverter generates -7.5V for negative CCD bias. The AUX3 controller generates a regulated current for a series network of four white LEDs that backlight the LCD. Figure 2. Typical Operating Circuit for 2 AA Cells Figure 2 is optimized for 2-cell AA inputs (1.5V to 3.7V) by connecting the step-down input (PVSD) to the main output (PVM). The main 3.3V output operates directly from the battery as a step-up (SUSD = PVSD). The 1.8V core output now operates as a boost-buck with efficiency up to 90%. The rest of the circuit is unchanged from Figure 1. Figure 3. Typical Operating Circuit for 2 AA Cells and 1-Cell Li+ The MAX1566/MAX1567 can also allow either 1-cell Li+ or 2 AA cells to power the same design. If the stepdown and main inputs are both connected to PVSU, then both the 3.3V and 1.8V outputs operate as boostbuck converters. There is an efficiency penalty compared to stepping down VSD directly from the battery, but that is not possible with a 1.5V input.
Multiple-Output Flyback Circuits
Some applications require multiple voltages from a single converter channel. This is often the case when generating voltages for CCD bias or LCD power. Figure 9 shows a two-output flyback configuration with an AUX channel. The controller drives an external MOSFET that switches the transformer primary. Two transformer secondaries generate the output voltages. Only one positive output voltage can be fed back, so the other voltages are set by the turns-ratio of the transformer secondaries. The load stability of the other secondary voltages depends on transformer leakage inductance and winding resistance. Voltage regulation is best when the load on the secondary that is not fed back is small compared to the load on the one that is fed back. Regulation also improves if the load-current range is limited. Consult the transformer manufacturer for the proper design for a given application.
Transformerless Inverter for Negative CCD Bias (AUX2, MAX1567)
On the MAX1567, AUX2 is set up to drive an external Pchannel MOSFET in an inverting configuration. DL2 drives low to turn on the MOSFET, and FB2 has inverted polarity and a 0V threshold. This is useful for generating negative CCD bias without a transformer, particularly with high pixel-count cameras that have a greater negative CCD load current. Figure 10 shows an example circuit.
Boost with Charge Pump for Positive and Negative Outputs
Another method of producing bipolar output voltages without a transformer is with an AUX controller and a charge-pump circuit, as shown in Figure 11. When MOSFET Q1 turns off, the voltage at its drain rises to supply current to VOUT+. At the same time, C1 charges to the voltage VOUT+ through D1. When the MOSFET turns on, C1 discharges through D3, thereby charging C3 to VOUTminus the drop across D3 to create roughly the same voltage as VOUT+ at VOUT-, but with inverted polarity.
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Six-Channel, High-Efficiency, Digital Camera Power Supplies
If different magnitudes are required for the positive and negative voltages, a linear regulator can be used at one of the outputs to achieve the desired voltages. One such connection is shown in Figure 12. This circuit is somewhat unique in that a positive-output linear regulator can regulate a negative voltage output. It does this by controlling the charge current flowing to the flying capacitor rather than directly regulating at the output. Using SDOK and AUX1OK for Power Sequencing SDOK goes low when the step-down reaches regulation. Some microcontrollers with low-voltage cores require that the high-voltage (3.3V) I/O rail not be powered up until the core has a valid supply. The circuit in Figure 15 accomplishes this by driving the gate of a PFET connected between the 3.3V output and the processor I/O supply. Figure 16 shows a similar application where AUX1OK gates 5V power to the CCD only after the +15V output is in regulation. Alternately, power sequencing can also be implemented by connecting RC networks to delay the appropriate converter ON_ inputs. Using SCF for Full-Load Startup The SCF output goes low only after the step-up reaches regulation. It can be used to drive a P-channel MOSFET switch that turns off the load of a selected supply in the event of an overload. Or, it can remove the load until the supply reaches regulation, effectively allowing fullload startup. Figure 17 shows such a connection for the step-up output.
MAX1566/MAX1567
SEPIC Boost-Buck
The MAX1566/MAX1567s' internal switch step-up, main, and step-down converters can be cascaded to make a high-efficiency boost-buck converter, but it is sometimes desirable to build a second boost-buck converter with an AUX_ controller. One type of step-up/step-down converter is the SEPIC, shown in Figure 13. Inductors L1 and L2 can be separate inductors or can be wound on a single core and coupled like a transformer. Typically, a coupled inductor improves efficiency since some power is transferred through the coupling so less power passes through the coupling capacitor (C2). Likewise, C2 should have low ESR to improve efficiency. The ripple-current rating must be greater than the larger of the input and output currents. The MOSFET (Q1) drain-source voltage rating and the rectifier (D1) reverse-voltage rating must exceed the sum of the input and output voltages. Other types of step-up/step-down circuits are a flyback converter and a step-up converter followed by a linear regulator.
Adding a MAX1801 Slave
The MAX1801 is a 6-pin, SOT-slave, DC-to-DC controller that can be connected to generate additional output voltages. It does not generate its own reference or oscillator. Instead, it uses the reference and oscillator of the MAX1566/MAX1567 (Figure 14). The MAX1801 controller operation and design are similar to that of the MAX1566/MAX1567 AUX controllers. All comments in the AUX Controller Component Selection section also apply to add-on MAX1801 slave controllers. For more details, refer to the MAX1801 data sheet.
Setting VSD Below 1.25V The step-down feedback voltage is 1.25V. With a standard two-resistor feedback network, the output voltage can be set to values between 1.25V and the input voltage. If a step-down output voltage less than 1.25V is desired, it can be set by adding a third feedback resistor from FBSD to a voltage higher than 1.25V. The stepup or main outputs are convenient for this, as shown in Figure 18.
The equation governing output voltage in Figure 18's circuit is as follows: 0 = [(VSD - VFBSD) / R1] + [(0 - VFBSD) / R2] + [(VSU - VFBSD) / R3] where VSD is the output voltage, VFBSD is 1.25V, and VSU is the step-up output voltage. Any available voltage that is higher than 1.25V can be used as the connection point for R3 in Figure 18, and for the VSD term in the equation. Since there are multiple solutions for R1, R2, and R3, the above equation cannot be written in terms of one resistor. The best method for determining resistor values is to enter the above equation into a spreadsheet and test estimated resistor values. A good starting point is with 100k at R2 and R3.
Applications for Status Outputs
The MAX1566/MAX1567 have three status outputs: SDOK, AUX1OK, and SCF. These monitor the output of the step-down channel, the AUX1 channel, and the status of the overload-short-circuit protection. Each output is open drain to allow the greatest flexibility. Figures 15, 16, and 17 show some possible connections for these outputs.
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Six-Channel, High-Efficiency, Digital Camera Power Supplies MAX1566/MAX1567
Designing a PC Board
Good PC board layout is important to achieve optimal performance from the MAX1566/MAX1567. Poor design can cause excessive conducted and/or radiated noise. Conductors carrying discontinuous currents and any high-current path should be made as short and wide as possible. A separate low-noise ground plane containing the reference and signal grounds should connect to the power-ground plane at only one point to minimize the effects of power-ground currents. Typically, the ground planes are best joined right at the IC. Keep the voltage-feedback network very close to the IC, preferably within 0.2in (5mm) of the FB_ pin. Nodes with high dV/dt (switching nodes) should be kept as small as possible and should be routed away from high-impedance nodes such as FB_. Refer to the MAX1566/MAX1567 EV kit data sheet for a full PC board example.
Chip Information
TRANSISTOR COUNT: 9420 PROCESS: BiCMOS
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Six-Channel, High-Efficiency, Digital Camera Power Supplies
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)
QFN THIN 6x6x0.8.EPS
MAX1566/MAX1567
D2 D D/2 k
C L
b D2/2
E/2 E2/2 E (NE-1) X e
C L
E2
k
e (ND-1) X e
L
C L
C L
L
L
e
e
A1
A2
A
PROPRIETARY INFORMATION TITLE:
PACKAGE OUTLINE 36, 40L QFN THIN, 6x6x0.8 mm
DOCUMENT CONTROL NO. REV.
APPROVAL
21-0141
1 2
B
COMMON DIMENSIONS
PKG. CODES T3666-1 T4066-1
EXPOSED PAD VARIATIONS
D2 E2 MIN. NOM. MAX. MIN. NOM. MAX. 3.60 4.00 3.70 4.10 3.80 4.20 3.60 4.00 3.70 4.10 3.80 4.20
NOTES: 1. DIMENSIONING & TOLERANCING CONFORM TO ASME Y14.5M-1994. 2. ALL DIMENSIONS ARE IN MILLIMETERS. ANGLES ARE IN DEGREES. 3. N IS THE TOTAL NUMBER OF TERMINALS. 4. THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL CONFORM TO JESD 95-1 SPP-012. DETAILS OF TERMINAL #1 IDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED WITHIN THE ZONE INDICATED. THE TERMINAL #1 IDENTIFIER MAY BE EITHER A MOLD OR MARKED FEATURE. 5. DIMENSION b APPLIES TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.25 mm AND 0.30 mm FROM TERMINAL TIP. 6. ND AND NE REFER TO THE NUMBER OF TERMINALS ON EACH D AND E SIDE RESPECTIVELY. 7. DEPOPULATION IS POSSIBLE IN A SYMMETRICAL FASHION. 8. COPLANARITY APPLIES TO THE EXPOSED HEAT SINK SLUG AS WELL AS THE TERMINALS.
PROPRIETARY INFORMATION
9. DRAWING CONFORMS TO JEDEC MO220. 10. WARPAGE SHALL NOT EXCEED 0.10 mm.
TITLE:
PACKAGE OUTLINE 36, 40L QFN THIN, 6x6x0.8 mm
DOCUMENT CONTROL NO. REV.
APPROVAL
21-0141
2 2
B
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 35 (c) 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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