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19-2883; Rev 0; 7/03
KIT ATION EVALU ABLE AVAIL
5-Channel Slim DSC Power Supplies
General Description Features
o Step-Up DC-DC Converter, 95% Efficient o Step-Down DC-DC Converter Operate from Battery for 95% Efficient Step-Down 90% Efficient Boost-Buck with Step-Up o Three Auxiliary PWM DC-DC Controllers o No Transformers (MAX1585) o Up to 1MHz Operating Frequency o 1mA Shutdown Mode o Internal Soft-Start Control o Overload Protection o Compact 32-Pin Thin QFN Package (5mm x 5mm)
MAX1584/MAX1585
The MAX1584/MAX1585 provide a complete powersupply solution for slim digital cameras. They improve performance, component count, and size compared to conventional multichannel controllers in 2-cell AA, 1-cell 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 MAX1584/MAX1585 include 5 high-efficiency DCDC conversion channels: * Step-up DC-DC converter with on-chip FETs * Step-down DC-DC converter with on-chip FETs * Three PWM DC-DC controllers for CCD, LCD, LED, or other functions The step-down DC-DC converter can operate directly from the battery or from the step-up output, providing boost-buck capability with a compound efficiency of up to 90%. Both devices include three PWM DC-DC controllers: the MAX1584 includes two step-up controllers and one step-down controller, while the MAX1585 includes one step-up controller, one inverting controller, and one step-down controller. All DC-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 MAX1584/MAX1585 are available in space-saving, 32-pin thin QFN packages. An evaluation kit is available to expedite designs.
Ordering Information
PART TEMP RANGE PINPACKAGE 32 Thin QFN 5mm x 5mm 32 Thin QFN 5mm x 5mm AUX FUNCTIONS 2 step-up 1 step-down 1 step-up 1 step-down 1 inverting
MAX1584ETJ -40C to +85C
MAX1585ETJ -40C to +85C
Applications
GND CC3 DL1
Pin Configuration
INDL2 25 24 23 22 CC2 FB2 PVSU LXSU PGSU OSC SCF SDOK 21 20 19 18 17 9 ON1 10 ON2 11 ON3 12 ONSU 13 REF 14 FBSU 15 CCSU 16 AUX1OK DL3 DL2 27 FB3 PV 26
Digital Cameras PDAs
32
31
30
29
28
Typical Operating Circuit
CC1 FB1 PGSD LXSD
1 2 3 4 5 6 7 8
INPUT 0.7V TO 5.5V
MAX1585
STEP-UP STEP-DOWN ONSU ONSD ON1 ON2 ON3 AUX1 AUX2 AUX3 SYSTEM +5V CORE +1.8V LCD, CCD, LED +15V CCD -7.5V LOGIC +3.3V
PVSD ONSD CCSD FBSD
MAX1584 MAX1585
THIN QFN 5mm x 5mm
________________________________________________________________ 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.
5-Channel Slim DSC Power Supplies MAX1584/MAX1585
ABSOLUTE MAXIMUM RATINGS
PV, PVSU, PVSD, SDOK, AUX1OK, SCF, ON_, FB_ to GND..........................................................................-0.3V to +6V PGND to GND.......................................................-0.3V to +0.3V INDL2, DL1, DL3 to GND.........................-0.3V to (PVSU + 0.3V) DL2 to GND ............................................-0.3V to (INDL2 + 0.3V) PV to PVSU ...........................................................-0.3V to + 0.3V LXSU 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) 32-Pin Thin QFN (derate 22mW/C above +70C) ....1700mW 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 PGND, and LXSD has internal clamp diodes to PVSD and PGND. Applications that forward bias these diodes should take care not to exceed the device's 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 = VPVSD = VINDL2 = 3.6V, TA = 0C to +85C, unless otherwise noted.)
PARAMETER GENERAL Input Voltage Range Step-Up Minimum Startup Voltage Shutdown Supply Current into PV Supply Current into PV with Step-Up Enabled Supply Current into PV with Step-Up and Step-Down 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 STEP-UP DC-DC CONVERTER Step-Up Startup-to-Normal Operating Threshold Step-Up Startup-to-Normal Operating Threshold Hysteresis Rising edge or falling edge (Note 4) 2.30 2.5 80 2.65 V mV 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 = ON1 = 3.6V, FBSU = 1.5V, FB2 = 1.5V (does not include switching losses) 0.7 0.9 0.1 300 450 5.5 1.1 5 450 700 V V A A A CONDITIONS MIN TYP MAX UNITS
400
650
A
2
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5-Channel Slim DSC Power Supplies
ELECTRICAL CHARACTERISTICS (continued)
(VPVSU = VPV = VPVSD = VINDL2 = 3.6V, TA = 0C to +85C, unless otherwise noted.)
PARAMETER Step-Up Voltage Adjust Range Start Delay of ONSD, ON1, ON2, 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 Step-Down Output Voltage Adjust 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 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 (Note 6) PVSU = 1.8V (Note 5) PVSU = 1.8V PVSU = 1.8V FBSU = 1V VLX = 0V, PVSU = 5.5V VLXSU = VOUT = 5.5V N channel P channel 2.4 80 FBSU = CCSU FBSU = 1.25V (Note 6) 1.231 80 -100 CONDITIONS MIN 3.0 1024 1.25 135 +1 150 0.275 85 0.1 0.1 95 150 2.8 20 450 700 200 90 5 5 150 250 3.2 1.269 185 +100 TYP MAX 5.5 UNITS V OSC cycles V S nA mA V/A % A A m A mA mA ns kHz
MAX1584/MAX1585
STEP-DOWN DC-DC CONVERTER PVSD must be greater than output (Note 7) 1.25 1.231 80 -100 1.25 135 +0.1 100 0.5 0.1 95 150 0.8 20 2048 0.01 0.01 0.1 1 5 150 250 0.95 5.00 1.269 185 +100 V V S nA mA V/A A m A mA OSC cycles V A
Idle Mode is a trademark of Maxim Integrated Products, Inc. _______________________________________________________________________________________ 3
5-Channel Slim DSC Power Supplies MAX1584/MAX1585
ELECTRICAL CHARACTERISTICS (continued)
(VPVSU = VPV = VPVSD = VINDL2 = 3.6V, TA = 0C to +85C, unless otherwise noted.)
PARAMETER AUX1, 2, 3 DC-DC CONTROLLERS Maximum Duty Cycle FB1 and FB3 Regulation Voltage FB2 (MAX1584) Regulation Voltage FB2 (MAX1585) (Inverter) Regulation Voltage FB_ to CC_ Transconductance FB_ Input Leakage Current DL_ Driver Resistance DL_ Drive Current Soft-Start Interval AUX1OK Output Low Voltage AUX1OK Leakage Current 0.1mA into AUX1OK ONSU = GND FB_ = 1V FB_ = CC_ FB_ = CC_ FB_ = CC_ FB_ = CC_ FB_ = 1.25V Output high or low Sourcing or sinking 80 1.231 1.231 -0.01 80 -100 85 1.25 1.25 0 135 +1 2.5 0.5 4096 0.01 0.01 0.1 1 90 1.269 1.269 +0.01 185 +100 10 % V V V S nA A OSC cycles V A OSC cycles 1 0.1 A V C C 0.2 0.4 VPVSU 0.2 1.6 330 k CONDITIONS MIN TYP MAX UNITS
OVERLOAD AND THERMAL PROTECTION Overload-Protection Fault Delay SCF Leakage Current SCF Output Low Voltage Thermal Shutdown Thermal Hysteresis LOGIC INPUTS ON_ Input Low Level 1.1V < PVSU < 1.8V (ONSU only) 1.8V < PVSU< 5.5V 1.1V < PVSU < 1.8V (ONSU only) 1.8V < PVSU < 5.5V ON_ Impedance to GND ON_ = 3.35V V ONSU = PVSU, FBSU = 1.5V 0.1mA into SCF 100,000 0.1 0.01 +160 20
ON_ Input High Level
V
4
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5-Channel Slim DSC Power Supplies
ELECTRICAL CHARACTERISTICS
(VPVSU = VPV = VPVSD = VINDL2 = 3.6V, TA = -40C to +85C, unless otherwise noted.) (Note 8)
PARAMETER GENERAL Input Voltage Range Shutdown Supply Current into PVSU Supply Current into PV with Step-Up Enabled Supply Current into PV with Step-Up and Step-Down 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 DC-DC CONVERTER 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 STEP-DOWN DC-DC CONVERTER Step-Down Output Voltage Adjust Range PVSD must be greater than output (Note 7) 1.25 5.00 V FBSU = CCSU FBSU = 1.25V FBSU = 1V VLX = 0V, PVSU = 5.5V VLXSU = VOUT = 5.5V N channel P channel 2.4 Rising edge or falling edge (Note 4) 2.30 3.0 1.225 80 -100 80 2.65 5.5 1.275 185 +100 90 5 5 150 250 3.2 V V V S nA % A A m A Rising edge OSC = 1.5V, IOSC = 3mA 1.225 1.275 80 V IREF = 20A 10A < IREF < 200A 2.7V < PVSU < 5.5V 1.225 1.275 10 5 V mV mV (Note 2) PVSU = 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 = ON1 = 3.6V, FBSU = 1.5V, FB2 = 1.5V (does not include switching losses) 0.7 5.5 5 450 700 V A A A CONDITIONS MIN MAX UNITS
MAX1584/MAX1585
650
A
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5-Channel Slim DSC Power Supplies MAX1584/MAX1585
ELECTRICAL CHARACTERISTICS (continued)
(VPVSU = VPV = VPVSD = VINDL2 = 3.6V, TA = -40C to +85C, unless otherwise noted.) (Note 8)
PARAMETER 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 Maximum Duty Cycle FB1 and FB3 Regulation Voltage FB2 (MAX1584) Regulation Voltage FB2 (MAX1585) (Inverter) Regulation Voltage FB_ to CC_ Transconductance FB_ Input Leakage Current DL_ Driver Resistance AUX1OK Output Low Voltage AUX1OK Leakage Current SCF Leakage Current SCF Output Low Voltage LOGIC INPUTS ON_ Input Low Level ON_ Input High Level 1.1V < PVSU < 1.8V (ONSU only) 1.8V < PVSU < 5.5V 1.1V < PVSU < 1.8V (ONSU only) 1.8V < PVSU < 5.5V VPVSU - 0.2 1.6 0.2 0.4 V V 0.1mA into SDOK ONSU = GND FB_ = 1V FB_ = CC_ FB_ = CC_ FB_ = CC_ FB_ = CC_ FB_ = 1.25V Output high or low 0.1mA into AUX1OK ONSU = GND ONSU = PVSU, FBSU = 1.5V 0.1mA into SCF 80 1.225 1.225 -0.01 80 -100 FBSD = CCSD FBSD = 1.25V VLXSD = 0 to 3.6V, PVSU = 3.6V N channel P channel 0.65 CONDITIONS MIN 1.225 80 -100 MAX 1.275 185 +100 5 150 250 0.95 0.1 1 90 1.275 1.275 +0.01 185 +100 10 0.1 1 1 0.1 UNITS V S nA A m A V A % V V V S nA V A A V
AUX1, 2, 3 DC-DC CONTROLLERS
OVERLOAD AND THERMAL PROTECTION
Note 2: The MAX1584/MAX1585 are powered from the step-up output (PVSU). An internal low-voltage startup oscillator drives the step-up starting at about 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 input battery to PVSU, is required for lowvoltage startup, or if PVSD is connected to VIN instead of PVSU. 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 Applications Information section.
6
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5-Channel Slim DSC Power Supplies
ELECTRICAL CHARACTERISTICS (continued)
(VPVSU = VPV = VPVSD = VINDL2 = 3.6V, TA = -40C to +85C, unless otherwise noted.) (Note 8) Note 5: The step-up current limit in startup refers to the LXSU switch current limit, not an output current limit. Note 6: The idle mode current threshold is the transition point between fixed-frequency PWM operation and idle mode operation (where switching rate varies with load). The specification is given in terms of inductor current. In terms of output current, the idle mode transition varies with input-output voltage ratio and inductor value. For the step-up, the transition output current is approximately 1/3 the inductor current when stepping from 2V to 3.3V. For the step-down, the transition current in terms of output current is approximately 3/4 the inductor current when stepping down from 3.3V to 1.8V. 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: Specifications to -40C are guaranteed by design, not production tested.
MAX1584/MAX1585
Typical Operating Characteristics
(Circuit of Figure 1, TA = +25C, unless otherwise noted.)
STEP-UP EFFICIENCY vs. LOAD CURRENT
MAX1584/85 toc01
STEP-DOWN EFFICIENCY vs. LOAD CURRENT
MAX1584/85 toc02
COMBINED BOOST-BUCK EFFICIENCY vs. LOAD CURRENT
90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 1 10 VOUT3 = 3.3V VOUTSU = 5.0V 100 1000 VIN = 4.5V VIN = 4.2V VIN = 3.8V VIN = 3.0V
MAX1584/85 toc03
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 1 10 100 LOAD CURRENT (mA) VOUT = 5V VIN = 4.5V VIN = 4.2V VIN = 3.8V VIN = 3.0V
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 1 10 100 VIN = 3.0V VIN = 3.8V VIN = 4.2V VIN = 4.5V PVSD CONNECTED TO BATTERY VOUT = 1.5V DOES NOT INCLUDE CURRENT USED BY THE STEP-UP TO POWER THE IC
100
1000
1000
LOAD CURRENT (mA)
LOAD CURRENT (mA)
EFFICIENCY vs. INPUT VOLTAGE
MAX1584/85 toc04
AUX1 EFFICIENCY vs. LOAD CURRENT
MAX5184/85 toc05
MAX1585 AUX2 EFFICIENCY vs. LOAD CURRENT
MAX5184/85 toc06
100 95 EFFICIENCY (%) 90 85 80 75 70 3.0 3.5 4.0 SU = 5V, 300mA SD = 1.5V, 250mA SU + AUX3 = 3.3V, 300mA AUX1 = 15V, 40mA AUX2 = -7.5V, 40mA
100 90 80 EFFICIENCY (%) 70 60 50 40 VOUT1 = 15V 30 VIN = 4.5V VIN = 4.2V VIN = 3.8V VIN = 3.0V
90 80 EFFICIENCY (%) 70 60 50 40 VOUT2 = -7.5V 30 1 10 100
VIN = 3.0V VIN = 3.8V VIN = 4.2V VIN = 4.5V
4.5
1
10
100
1000
1000
INPUT VOLTAGE (V)
LOAD CURRENT (mA)
LOAD CURRENT (mA)
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5-Channel Slim DSC Power Supplies MAX1584/MAX1585
Typical Operating Characteristics (continued)
(Circuit of Figure 1, TA = +25C, unless otherwise noted.)
NO-LOAD INPUT CURRENT vs. INPUT VOLTAGE (SWITCHING)
8 7 INPUT CURRENT (mA) 6 5 4 3 2 1 0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 INPUT VOLTAGE (V) VSU = 5.0V BOOST-BUCK (SU + AUX3) VSU = 5.0V, OUT3 = 3.33V
MAX1584/85 toc07
MINIMUM STARTUP VOLTAGE vs. LOAD CURRENT (VSU)
3.0 2.5 2.0 1.5 1.0 0.5 0 0 200 400 600 800 1000 LOAD CURRENT (mA) SCHOTTKY DIODE CONNECTED FROM IN TO VSU
MAX5184/85 toc08
9
3.5 MINIMUM STARTUP VOLTAGE (V)
REFERENCE VOLTAGE vs. TEMPERATURE
MAX1584/85 toc09
REFERENCE VOLTAGE vs. REFERENCE LOAD CURRENT
MAX1584/85 toc10
1.254
1.250 1.249 REFERENCE VOLTAGE (V) 1.248 1.247 1.246 1.245
REFERENCE VOLTAGE (V)
1.251
1.248
1.246
1.243 -50 -25 0 25 50 75 100 TEMPERATURE (C)
1.244 0 50 100 150 200 250 300 REFERENCE LOAD CURRENT (A)
OSCILLATOR FREQUENCY vs. ROSC
MAX1584/85 toc11
SWITCHING FREQUENCY vs. TEMPERATURE
509 SWITCHING FREQUENCY (kHz) 508 507 506 505 504 503 502 ROSC= 51k COSC= 100pF -50 -25 0 25 50 75 100
MAX1584/85 toc12
1100 COSC = 470pF OSCILLATOR FREQUENCY (kHz) 900 700 500 300 100 -100 1 10 ROSC (k) 100 COSC = 330pF COSC = 220pF COSC = 100pF COSC = 47pF
510
501 1000 TEMPERATURE (C)
8
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5-Channel Slim DSC Power Supplies
Typical Operating Characteristics (continued)
(Circuit of Figure 1, TA = +25C, unless otherwise noted.)
AUX MAXIMUM DUTY CYCLE vs. FREQUENCY
87 MAXIMUM DUTY CYCLE (%) 86 85 84 83 82 81 COSC = 330pF 80 0 100 200 300 400 500 600 700 800 900 1000 FREQUENCY (kHz) 200s/div 0A VIN = 3.5V IIN 1.0A/div WHEN THIS DUTY CYCLE IS EXCEEDED FOR 100,000 CLOCK CYCLES, THE MAX1584/MAX1585 SHUT DOWN
MAX1584/85 toc13
MAX1584/MAX1585
STEP-UP STARTUP RESPONSE
MAX1584/85 toc14
88
0V 0V 0A
ONSU 5V/div OUTSU 5V/div IOUTSU 200mA/div
STEP-DOWN STARTUP RESPONSE
MAX1584/85 toc15
AUX1 STARTUP RESPONSE
MAX1584/85 toc16
ONSD 5V/div 0V OUTSD 5V/div 0V
ON1 5V/div OUT1 10V/div
0V IOUTSD 200mA/div 0A
0V IOUT1 100mA/div
0A VIN = 3.5V 4ms/div 2ms/div VIN = 3.5V
STEP-UP LOAD-TRANSIENT RESPONSE
MAX1584/85 toc17
STEP-DOWN LOADTRANSIENT RESPONSE
MAX1584/85 toc18
0V
VOUTSU AC-COUPLED 500mV/div
0V
VOUTSD AC-COUPLED 100mV/div
0A
VOUTSU = 5.0V VIN = 3.5V 400s/div
IOUT_SU 200mA/div
0A
VIN = 3.5V VOUT_SD = 1.5V 400s/div
IOUT_SD 100mA/div
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5-Channel Slim DSC Power Supplies MAX1584/MAX1585
Pin Description
PIN 1 NAME CC1 FUNCTION AUX1 Controller Compensation Node. Connect a series resistor-capacitor from CC1 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. Step-Down Power Ground. Connect all PG_ pins together and to GND with short traces as close as possible to the IC. Step-Down Converter Switching Node. Connect to the inductor of the step-down converter. LXSD is high impedance in shutdown. Step-Down Converter Input. PVSD can connect to PVSU, effectively making OUTSD a boost-buck output from the battery. Bypass to GND with a 1F ceramic capacitor if connected to PVSU. PVSD can also be connected to the battery but should not exceed PVSU by more than a Schottky diode forward voltage. Bypass PVSD with a 10F ceramic capacitor when connecting to the battery input. A 10k internal resistance connects PVSU and PVSD. Step-Down Converter On/Off Control Input. Logic high = on; however, turn-on is locked out until the stepup has reached regulation. This pin has an internal 330k pulldown resistance to GND. Step-Up Converter Compensation Node. Connect a series resistor-capacitor from CCSD to GND to compensate the converter control loop. This pin is actively driven to GND in shutdown, overload, and thermal limit. See the Step-Down Compensation section. Step-Down Converter Feedback Input. Connect a resistive voltage-divider from OUTSD to FBSD to GND. The FBSD 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. 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. 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. 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-DC converter output has reached its final value. This pin has an internal 330k pulldown resistance to GND. Reference Output. Bypass REF to GND with a 0.1F or greater capacitor. The maximum allowed load on REF is 200A. REF is actively pulled to GND when all converters are shut down. Step-Up Converter Feedback Input. Connect a resistive voltage-divider from PVSU to FBSU to GND. The FBSU feedback threshold is 1.25V. This pin is high impedance in shutdown. Step-Up Converter Compensation Node. Connect a series resistor-capacitor from CCSU to GND to compensate the converter control loop. This pin is actively driven to GND in shutdown, overload, and thermal limit. See the Step-Up Compensation section.
2 3 4
FB1 PGSD LXSD
5
PVSD
6
ONSD
7
CCSD
8 9 10 11
FBSD ON1 ON2 ON3
12
ONSU
13 14
REF FBSU
15
CCSU
10
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5-Channel Slim DSC Power Supplies
Pin Description (continued)
PIN 16 17 NAME AUX1OK SDOK FUNCTION Open-Drain Power-OK Signal for AUX1 Controller. AUX1OK is low when the AUX1 controller has successfully completed soft-start. This pin is high impedance in shutdown, overload, and thermal limit. Open-Drain Power-OK Signal for Step-Down Converter. SDOK is low when the step-down has successfully completed soft-start. This pin is high impedance in shutdown, overload, and thermal limit. Short-Circuit Flag, Active-Low, Open-Drain Output. SCF is high impedance 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. 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. Step-Up Power Ground. Connect all PG_ pins together and to GND with short 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-DC Converter. Connect the output filter capacitor from PVSU to PGSU. PVSU can also power other converter channels. Connect PVSU to PV at the IC. MAX1585 (AUX2 inverter): The FB2 feedback threshold is 0V. Connect a resistive voltage-divider from the output voltage to FB2 to REF to set the output voltage. MAX1584 (AUX2 step-up): The FB2 feedback threshold is 1.25V. Connect a resistive voltage-divider from the output voltage to FB2 to GND to set the output voltage.
MAX1584/MAX1585
18
SCF
19
OSC
20 21 22
PGSU LXSU PVSU
23
FB2
AUX2 Controller Feedback Input. This pin is high impedance in shutdown.
24
CC2
AUX2 Controller Compensation Node. Connect a series resistor-capacitor from CC2 to GND to compensate the control loop. CC2 is actively driven to GND in shutdown and thermal limit. See the AUX Compensation section. MAX1585 (AUX2 inverter): Connect INDL2 to the external P channel MOSFET source (typically the battery) to ensure the P channel is completely off when D2 swings high. MAX1584 (AUX2 step-up): Connect INDL2 to PVSU for optimum N-channel gate drive.
25
INDL2
Voltage Input for the AUX2 Gate Driver. The voltage at INDL2 sets the high gate-drive voltage.
26
PV
IC Power Input. Connect PVSU and PV together. MAX1585: DL2 drives a PFET in an inverter configuration. In shutdown, overload, and thermal limit, DL2 is driven high. MAX1584: DL2 drives an N-channel FET in a boost/flyback configuration. In shutdown, overload, and thermal limit, DL2 is driven low.
27
DL2
AUX2 Controller Gate-Drive Output. DL2 drives between INDL2 and GND.
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5-Channel Slim DSC Power Supplies MAX1584/MAX1585
Pin Description (continued)
PIN 28 29 30 31 NAME DL3 DL1 GND CC3 FUNCTION AUX3 Step-Down Controller Gate-Drive Output. Connect to the gate of a P-channel MOSFET. DL3 swings from GND to PVSU and supplies up to 500mA. DL3 is driven to PVSU in shutdown and thermal limit. AUX1 Step-Up Controller Gate-Drive Output. Connect to the gate of an N-channel MOSFET. DL1 swings from GND to PVSU and supplies up to 500mA. DL1 is driven to GND in shutdown and thermal limit. Analog Ground. Connect to all PG_ pins as close to the IC as possible. AUX3 Step-Down Controller Compensation Node. Connect a series resistor-capacitor from CC3 to FB3 to compensate the converter control loop. This pin is actively driven to GND in shutdown, overload, and thermal limit. See the AUX Compensation section. PWM Step-Up Controller 3 Feedback Input. Connect a resistive voltage-divider from the output voltage to FB3 to GND to set the output voltage. The FB3 feedback threshold is 1.25V. This pin is high impedance in shutdown. Exposed Underside Metal Pad. This pad must be soldered to the PC board to achieve package thermal and mechanical ratings. There is no internal metal or bond wire physically connecting the exposed pad to the GND pin(s). Connecting the exposed pad to ground does not remove the requirement for a good ground connection to the appropriate IC pins.
32
FB3
PAD
EP
Detailed Description
The MAX1584/MAX1585 are complete power-conversion ICs for slim digital still cameras. They can accept input from a variety of sources, including single-cell Li+ batteries and 2-cell alkaline or NiMH batteries, as well as systems designed to accept both battery types. The MAX1584/MAX1585 include five DC-DC converter channels to generate all required voltages (Figure 2 shows a functional diagram): * Synchronous-rectified step-up DC-DC converter with on-chip MOSFETs--Typically supplies 3.3V for main system power or 5V to power other DC-DC converters for boost-buck designs. * Synchronous-rectified step-down DC-DC converter with on-chip MOSFETs--Typically supplies 1.8V for the DSP core. Powering the step-down from the step-up output provides efficient (up to 90%) boostbuck functionality that supplies a regulated output when the battery voltage is above or below the output voltage. The step-down can also be powered from the battery if there is sufficient headroom. * AUX1 step-up controller--Typically used for 15V to bias one or more of the LCD, CCD, and LED backlights.
* AUX2 step-up controller (MAX1584)--Typically supplies remaining bias voltages with either a multi-output flyback transformer or a boost converter with charge-pump inverter. Alternately, can power white LEDs for LCD backlighting. * AUX2 inverter controller (MAX1585)--Typically supplies negative CCD bias when high current is needed for large pixel-count CCDs. * AUX3 step-down controller--Typically steps 5V generated at PVSU down to 3.3V for system logic in boost-buck designs.
Step-Up DC-DC Converter
The step-up DC-DC switching converter is typically 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 a PFET 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 250mA for each pulse.
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5-Channel Slim DSC Power Supplies MAX1584/MAX1585
VIN 1.5V TO 4.2V C24 10F INDL2 P1 DL2 -7.5V -CDD BIAS R8 526k D2 C8 4.7F FB2 L6 3.6H P2 R9 93.1k 0.1F AUX3 V-MODE STEP-DOWN PWM 1.25V REF FB3 20k TO PVSU 330pF PVSU CCSU CCSD CC1 CC2 CC3 R5 10k R4 61.9k C4 470pF TO FB3 C3 1500pF C5 1500pF CURRENTMODE STEPDOWN L1 5H C11 47F 5V 1A MAIN SYSTEM R12 274k OSC PV D4 TO VIN AUX2 V-MODE INV PWM AUX1 V-MODE STEP-UP PWM N1 DL1 D1 C6 4.7F R6 1M
MAX1585
L3 2H
+15V, 80mA +CCD LCD LED
FB1 TO PVSU C23 OR VIN 10F L4 10H D3 C25 47F
R7 90.9k
REF
DL3
3.3V 250mA LOGIC R14 30.1k C20 560pF R22 1.2k
R15 18.2k
R1 47k C1 0.01F
R2 25k
R3 20k
CURRENTMODE STEP-UP
LXSU
PGSU FBSU PVSD C19 10F ONSU ONSD ON1 ON2 ON3 AUX1OK FBSD SCF SDOK LXSD
R13 90.9k
C2 4700pF
TO VIN OR PVSU L2 22H C9 30F +1.5V 250mA CORE R10 18.2k
PGSD
R11 90.9k
GND
Figure 1. MAX1584/MAX1585 Typical Application for 2-Cell AA or 1-Cell Li+ Battery
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5-Channel Slim DSC Power Supplies MAX1584/MAX1585
PVSU
INTERNAL POWER-OK
NORMAL MODE
2.35V ONSU
STARTUP OSCILLATOR
MAX1584/ MAX1585
REFOK OVER TEMP SCF FAULT 100,000 IN CLOCK CYCLE FAULT TIMER CLK
VREF
1V ONSU
FLTALL TO INTERNAL POWER PV
OSC 1.25V REFERENCE
REF
REF
150ns ONE-SHOT
GND
CCSU FAULT
PVSU
FBSU CURRENT-MODE DC-DC STEP-UP STEP-UP SOFT-START DONE (SUSSD) SOFT-START RAMP GENERATOR
LXSU
PGSU TO VREF ONSU FLTALL
CCSD FAULT FBSD CURRENT-MODE DC-DC STEP-DOWN SOFT-START RAMP GENERATOR
PVSD
LXSD
TO VREF
PGSD
ONSD SUSSD FLTALL TO AUX_ CHANNELS (SEE FIGURE 3)
SDOK
Figure 2. MAX1584/MAX1585 Functional Diagram 14 ______________________________________________________________________________________
5-Channel Slim DSC Power Supplies
Step-Down DC-DC Converter
The step-down DC-DC converter is optimized for generating low output voltages (down to 1.25V) at high efficiency. Output voltages lower than 1V can be set by adding an additional resistor (see the Applications Information section). 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 step-down can also operate with the step-up 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-DC is inactive until the step-up DC-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 13. Boost-Buck Operation The step-down input can be powered from the output of the step-up. By cascading these two channels, the step-down output can maintain regulation even as the battery voltage falls below the step-down output voltage. This is especially useful when trying to generate 3.3V from 1-cell Li+ inputs, or 2.5V from 2-cell alkaline or NiMH inputs, or when designing a power supply that must operate from both Li+ and alkaline/NiMH inputs. Compound efficiencies of up to 90% can be achieved when the step-up and step-down are operated in series. Note that the step-up output supplies both the step-up load and the step-down input current when the stepdown is powered from the step-up. The step-down input current reduces the available step-up output current for other loads. Direct Battery Step-Down Operation The step-down converter can also be operated directly from the battery as long as the voltage at PVSD does not exceed PVSU by more than a Schottky diode forward voltage. When using this connection, connect an external Schottky diode from the battery input to PVSU. On the MAX1584/MAX1585, there is an internal 10k resistance from PVSU to PVSD. This adds a small additional current drain (of approximately (VPVSU - VPVSD) / 10k) from PVSU when PVSD is not connected directly to PVSU. Step-down direct battery operation improves efficiency for the step-down output (up to 95%), but restricts the upper limit of the output voltage to 200mV less than the minimum battery voltage. In 1-cell Li+ designs (with a 2.7V min), the output can be set up to 2.5V. In 2-cell alkaline or NiMH designs, the output can be limited to 1.5V or 1.8V, depending on the minimum-allowed cell voltage. The step-down can only be briefly operated in dropout since the MAX1584/MAX1585 fault protection detects the out-of-regulation condition and activates after 100,000 OSC cycles (200ms at fOSC = 500kHz). At that point, all MAX1584/MAX1585 channels shut down.
MAX1584/MAX1585
AUX1, AUX2, and AUX3 DC-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. The MAX1584 contains two step-up/flyback controllers (AUX1 and AUX2) and one step-down controller (AUX3). The MAX1585 contains one step-up controller (AUX1), one inverting controller (AUX2), and one step-down controller (AUX3). Figure 3 shows a functional diagram of the AUX controllers. The inverting and step-down controllers differ from the step-up controllers only in the gate-drive logic and FB polarity and threshold. The sawtooth oscillator signal at OSC governs timing. At the start of each cycle, DL_ turns on the external MOSFET switch. For step-up controllers, DL_ goes high, while for inverting and step-down controllers, DL_ goes low (to turn on PFETs). The external MOSFET 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_ so that high DC loop gain and accuracy can be maintained. In step-up and step-down controllers, the FB_ threshold is 1.25V, and higher FB_ voltages reduce the MOSFET duty cycle. In inverting controllers, the FB_ threshold is 0V, and lower (more negative) FB_ voltages reduce the MOSFET duty cycle. Auxiliary controllers do not start until the step-up DC-DC output is in regulation. If the step-up, step-down, or any of the auxiliary controllers remains faulted for 100,000
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5-Channel Slim DSC Power Supplies MAX1584/MAX1585
FB_ MAX1584 AUX1 AND AUX2, MAX1585 AUX1 STEP-UP CONTROLLER CC_ LEVEL SHIFT REFI REF 0.85 REF R S Q DL_
FB2 MAX1585 AUX2 INVERTING CONTROLLER
CC2 LEVEL SHIFT REFI REF 0.85 REF R S Q DL2
SOFT-START (REFI RAMPS FROM 0V TO REF IN 1024 OSC CYCLES)
SOFT-START (REFI RAMPS FROM REF TO 0V IN 1024 OSC CYCLES)
CLK OSC FAULT PROTECTION OSC
CLK
ENABLE
FAULT PROTECTION
ENABLE
FB3 MAX1584 AND MAX1585 AUX3 STEP-DOWN CONTROLLER CC3 LEVEL SHIFT REFI REF 0.85 REF R S Q DL3
SOFT-START (REFI RAMPS FROM 0V TO REF IN 1024 OSC CYCLES)
CLK OSC FAULT PROTECTION
ENABLE
Figure 3. AUX Controller Functional Diagrams
OSC cycles, then all MAX1584/MAX1585 channels latch off. Maximum Duty Cycle The MAX1584/MAX1585 auxiliary PWM controllers have a guaranteed maximum duty cycle of 80%. In boost designs that employ continuous current, the maximum duty cycle limits the boost ratio so that:
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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-DC boost and flyback designs (Figure 5). Its output (DL1) is designed
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5-Channel Slim DSC Power Supplies
to drive an N-channel MOSFET. Its feedback (FB1) threshold is 1.25V. AUX2 In the MAX1584, AUX2 is identical to AUX1. In the MAX1585, AUX2 is an inverting controller that generates a regulated negative output voltage, typically for CCD and LCD bias. This is handy in height-limited designs where transformers might not be desired. The AUX2 MOSFET driver (DL2) in the MAX1585 is designed to drive P-channel MOSFETs. DL2 swings from GND to PVSU. See Figure 8 for a typical inverter configuration. AUX3 DC-DC Step-Down Controller AUX3 can be used for conventional DC-DC step-down (buck) designs (Figure 1). Its output (DL3) is designed to drive a P-channel MOSFET and swings from GND to PVSU. Its feedback (FB3) threshold is 1.25V. 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 15, where SCF provides load disconnect for the step-up on fault and power-up.
MAX1584/MAX1585
Soft-Start
The MAX1584/MAX1585 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. Soft-start is not included in the step-up converter in order to avoid limiting startup capability with loading. The step-down soft-start ramp takes half the time (2048 clock cycles) of the other channel ramps. This allows the step-down and AUX3 output (when set to 3.3V) 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 AUX3 output (3.3V typ) continues to rise at the same ramp rate.
Master/Slave Configurations
The MAX1584/MAX1585 support the MAX1801 slave PWM controllers that obtain input power, a voltage reference, and an oscillator signal directly from the MAX1584/MAX1585 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 since their operating frequency is synchronized to that of the MAX1584/MAX1585 master converter. A MAX1801 connection to the MAX1584/MAX1585 is shown in Figure 12.
Fault Protection
The MAX1584/MAX1585 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-DC converter channel (step-up, 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 DCDC converter is reinitialized by the ONSU pin or by cycling the input power. The fault-detection circuitry for any channel is disabled during its initial turn-on softstart 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. The step-up UVLO immediately triggers and shuts down all channels. The step-up then continues to attempt to start. If the step-up output short remains, these attempts do not 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
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Status Outputs (SDOK, AUX1OK, SCF)
The MAX1584/MAX1585 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. 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 enable 3.3V power to the CPU I/O after the CPU core is powered up (Figure 13), 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 gates 5V power to the CCD until the +15V CCD bias (generated by AUX1) is powered up (Figure 14).
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5-Channel Slim DSC Power Supplies MAX1584/MAX1585
VSU
ROSC OSC COSC VREF (1.25V) 150ns ONE-SHOT
MAX1584 MAX1585 (PARTIAL)
AUX PWM PVSU DL_
TO VBATT
Q1
D6
+15V 50mA LCD
MAX1584 MAX1585
FB_
NOTE: THIS CIRCUIT CAN OPERATE WITH AUX1 OR AUX2 ON THE MAX1584, AND WITH AUX1 ON THE MAX1585
Figure 4. Oscillator Functional Diagram
Figure 5. +15V LCD Bias with Basic Boost Topology
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 15.
activates the internal MOSFET switch to discharge the capacitor within a 150ns interval, 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.
Reference
The MAX1584/MAX1585 have internal 1.250V references. 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 when 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. If the application requires that REF be loaded beyond 200A, buffer REF with a unity-gain amplifier or op amp.
Low-Voltage Startup Oscillator
The MAX1584/MAX1585 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 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 MAX1584/MAX1585 operate with inputs as low as 0.7V since internal power for the IC is supplied by PVSU. At low input voltages, the stepup can have difficulty starting into heavy loads (see the Minimum Startup Voltage vs. Load Current graph in the Typical Operating Characteristics section); 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 15).
Oscillator
All MAX1584/MAX1585 DC-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 4). 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
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ON_ Control Inputs
The step-up converter activates with a high input at ONSU. The step-down and auxiliary DC-DC converters 1, 2, and 3 activate with a high input at ONSD, ON1, ON2, and ON3, respectively. The step-down and auxil-
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5-Channel Slim DSC Power Supplies
iary converters and 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-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: VRIPPLE = IL(PEAK) [1 / (2 x fOSC x COUT)] If the capacitor has significant ESR, the output ripple component due to capacitor ESR is: VRIPPLE(ESR) = IL(PEAK) x ESR Output capacitor specifics are also discussed in each converter's Compensation section.
MAX1584/MAX1585
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 ln(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 x ln[1 - 1.25 VPVSU]) See the Typical Operating Characteristics section for fOSC vs. ROSC using different values of COSC.
Step-Up Component Selection
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 Schottky diode from the battery to PVSU. See the Minimum Startup Voltage vs. Load Current graph in the Typical Operating Characteristics section. 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 half 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 x IOUT / (1 - D). The peak inductor current is as follows:
Setting Output Voltages
The MAX1584/MAX1585 step-up and step-down converters and the AUX1 controllers have resistoradjustable output voltages. When setting the voltage for all channels except AUX2 on the MAX1585, connect a resistive voltage-divider from the output voltage to the corresponding FB_ input. The FB_ input bias current is less than 100nA, so choose the low-side (FB_-to-GND) resistor (RL) to be 100k or less. Then calculate the high-side (output-to-FB_) resistor (RH): RH = RL [(VOUT / 1.25) - 1] AUX2 is an inverter on the MAX1585, so the FB2 threshold on the MAX1585 is 0V. To set the MAX1585 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 (negative output-to-FB2) resistor: RTOP = RREF (-VOUT(AUX2) / 1.25)
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5-Channel Slim DSC Power Supplies MAX1584/MAX1585
IIND(PK) = 1.25 x 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 might 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 helps 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 FBSU to CCSU), g MEA (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, R LOAD , in = VSUOUT / 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 CP is required (if calculated to be >10pF). For continuous conduction, the right-half-plane zero frequency (fRHPZ) is given by the following: fRHPZ = VSUOUT (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 (f C ) 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-DC converter, if LIDEAL is used, output current relates to inductor current by: IIND(PK) = 1.25 x IOUT / (1 - D) = 1.25 x 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 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)
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5-Channel Slim DSC Power Supplies
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 CCSU to GND: CP = COUT x RESR / RC If CP is calculated to be <10pF, it can be omitted. choose fC = 24kHz and calculate CC: CC = (VFB / VOUT)(RLOAD / RCS)(gM / 2 x fC) = (1.25 / 1.5)(6 / 0.6) x (135S / (6.28 x 40kHz)) = 4.5nF Choose 4.7nF. Now select RC so transient-droop requirements are met. For 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 x IIND(PK) / 6.75A In a step-down DC-DC converter, If LIDEAL is used, output current relates to inductor current by the following: IIND(PK) = 1.25 x IOUT So for a 250mA output load step with VIN = 3.5V and VOUT = 1.5V: RC = (1.25 x 0.6 x 0.25) / 6.75A = 27.8k Choose 27k. The inductor does somewhat limit the response in this case since it ramps at (VIN - VOUT) / 22H, or (3.5 - 1.5) / 22H = 90mA/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 4.7nF / 6 = 21F Choose 22F or greater. If the output filter capacitor has significant ESR, a zero occurs at: 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 CCSD to GND: CP = COUT x RESR / RC If CP is calculated to be <10pF, it can be omitted.
MAX1584/MAX1585
Step-Down Component Selection
Step-Down Inductor The external components required for the step-down are an inductor, input and output filter capacitors, and a compensation RC network. The MAX1585/1585 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 which sets the peak-to-peak inductor current at half the DC inductor current. D is the duty cycle: D = VOUT / VIN Given LIDEAL, the peak-to-peak inductor current is 0.5 x IOUT. The absolute peak inductor current is 1.25 x 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 with typically larger inductor size. Step-Down Compensation The relevant characteristics for step-down compensation are as follows: * Transconductance (from FBSD to CCSD), g MEA (135S) * Current-sense amplifier transresistance, RCS (0.6V/A) * Feedback regulation voltage, VFB (1.25V) * Step-down output voltage, VSD, in V * Output load equivalent resistance, R LOAD , in = VSD / ILOAD The key steps for step-down compensation are as follows: 1) Set the compensation RC zero to cancel the RLOAD COUT pole. 2) Set the loop crossover below 1/10 the switching frequency. If we assume VIN = 3.5V, VOUT = 1.5V, and IOUT = 250mA, then RLOAD = 6. If we select fOSC = 500kHz and L = 22H,
AUX Controller Component Selection
External MOSFET MAX1584/MAX1585 AUX1(step-up) controllers drive external logic-level N-channel MOSFETs. AUX3 (stepdown) controllers drive P-channel MOSFETs. AUX2 (step-up) on the MAX1584 drives an N channel, while AUX2 (inverting) on the MAX1585 drives a P channel.
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______________________________________________________________________________________
5-Channel Slim DSC Power Supplies
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) DL1 and DL3 swing between PVSU and GND. DL2 swings between INDL2 and GND. Use a MOSFET with on-resistance specified at or below the DL_ drive 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 onresistance 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 the MOSFET on-resistance. The transition loss is approximately: 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 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
22
MAX1584/MAX1585
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. 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 voltage ramp of 1.25V. 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 inductor-current boost operation, there is a right-halfplane zero, ZRHP, at the following: ZRHP = (1 - D)2 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 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 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)
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5-Channel Slim DSC Power Supplies
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 < f0SC / 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. AUX3 Step-Down Compensation It is expected that most AUX3 step-down applications employ continuous inductor current to optimize inductor size and efficiency. To ensure stability, the controlloop gain should cross over (drop below unity gain) at a frequency (fC) much less than that of the switching frequency. The relevant characteristics for voltage-mode stepdown compensation are as follows: * Transconductance (from FB3 to CC3), gMEA (135S) * Oscillator ramp voltage, VRAMP (1.25V) * Feedback regulation voltage, VFB (1.25V) * Output voltage, VOUT3, in V * Output load equivalent resistance, RLOAD, in = VOUT3 / ILOAD * Characteristic impedance of the LC output filter, RO = (L / C)1/2 The key steps for AUX3 step-down compensation are as follows: 1) Place fC sufficiently below the switching frequency (fOSC / 10). 2) Calculate COUT. 3) Calculate the complex pole pair due to the output LC filter. 4) Add two zeros to cancel the complex pole pair. 5) Add two high-frequency poles to optimize gain and phase margin. If we assume V IN = 5V, V OUT = 3.3V, and I OUT = 300mA, then RLOAD = 11. If we select fOSC = 500kHz and L = 10H, select the crossover frequency to be 1/10 the OSC frequency: fC = fOSC / 10 = 50kHz For 3.3V output, select R14 = 30.1k and R15 = 18.2k. See the Setting Output Voltages section. Calculate the equivalent impedance, REQ: REQ = RSOURCE + RL + ESR + RDS(ON) where RSOURCE is the output impedance of the source (this is the output impedance of the step-up converter when the AUX3 step-down is powered from the stepup), RL is the inductor DC resistance, ESR is the filtercapacitor equivalent resistance, and RDS(ON) is the on-resistance of the external MOSFET. The output impedance of the step-up converter (RSOURCE) is approximately 1 at f0. Since the sum of RL + ESR + RDS(ON) is small compared to 1, assume REQ = 1. Choose COUT so RO is less than REQ / 2: COUT > L / [(REQ / 2)2] = 10H / 0.25 = 40F Choose COUT = 47F: C4 = (VIN / VRAMP)(1 / [2 x R14 x fC]) = (5 / 1.25)(1/ [2 x 30.1k x 50kHz) = 423pF Choose C4 = 470pF. Cancel one pole of the complex pole pair by placing the R4 C4 zero at 0.75 f0. The complex pole pair is at the following: f0 = 1 / [2(L x COUT)1/2] = 1 / [2(10H x 47F)1/2] = 7.345kHz Choose R4 = 1 / (2 x C4 x 0.75 x f0) = 1 / (2 x 470pF x 0.75 x 7.345kHz) z Choose R4 = 61.9k (standard 1% value). Ensure that R4 > 2 / gMEA = 14.8k. If it is not greater, reselect R14 and R15. Cancel the second pole of the complex pole pair by placing the R14 C20 zero at 1.25 x f0. C20 = 1 / (2 x R14 x 1.25 x f0) = 1 / (2 x 30.1k x 1.25 x 7.345kHz) = 576pF Choose C20 = 560pF. Roll off the gain below the switching frequency by placing a pole at fOSC / 2: R22 = 1 / (2 x C20 [fOSC / 2]) = 1 / (2 x 560pF x 250kHz) = 1.137k Choose R22 = 1.2k. If the output filter capacitor has significant ESR, a zero occurs at the following: ZESR = 1 / (2 x COUT x RESR) Use the R4 C22 pole to cancel the ESR zero: C22 = COUT x RESR / R4 If C22 is calculated to be <10pF, it can be omitted.
23
MAX1584/MAX1585
______________________________________________________________________________________
5-Channel Slim DSC Power Supplies MAX1584/MAX1585
MAX1585 AUX2 Inverter Compensation, Discontinuous Inductor Current If the load current is very low (40mA or less), 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: 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 voltage ramp of 1.25V. The CC RC zero then is used to cancel the fP pole, so: RC = (RLOAD x COUT) / (2 CC) MAX1585 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 so 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)]
24
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 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.
Applications Information
LED, LCD, and Other Boost Applications
Any AUX channel 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 5 and 6 show examples of these applications.
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 7 shows a two-output flyback configuration with AUX_. 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.
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5-Channel Slim DSC Power Supplies MAX1584/MAX1585
TO VBATT
1F TO VBATT PVSU 1F DL_ +15V 50mA CCD+
MAX1584 MAX1585 (PARTIAL)
AUX_ PWM AUX PWM PVSU DL_
WHITE LEDS FB_
Q1
D2 -7.5V 30mA CCD-
62 (FOR 20mA)
MAX1585 (PARTIAL)
FB_ NOTE: THIS CIRCUIT CAN OPERATE WITH AUX1 OR AUX2 ON THE MAX1584, AND WITH AUX1 ON THE MAX1585.
NOTE: THIS CIRCUIT CAN OPERATE WITH AUX1 OR AUX2 ON THE MAX1584, AND WITH AUX1 ON THE MAX1585.
Figure 6. AUX_ Channel Powering a White LED Step-Up Current Source
Figure 7. +15V and -7.5V CCD Bias with Transformer
Transformerless Inverter for Negative CCD Bias (AUX2, MAX1585)
On the MAX1585, 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. Figures 1 and 8 show such a configuration for the MAX1585.
connection is shown in Figure 10. This circuit is somewhat unique in that a positive-output linear regulator is able to 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.
SEPIC Boost-Buck
The MAX1584/MAX1585s' internal switch step-up and step-down 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 11. 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.
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 9. 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. 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
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25
5-Channel Slim DSC Power Supplies MAX1584/MAX1585
TO VBATT
+15V 20mA
MAX1585 (PARTIAL)
INDL2 DL2
TO VBATT
FB_
AUX_ PWM PVSU
-7.5V 100mA AUX2 INVERTING PWM RTOP FB2 RREF REF
DL_
-7.5V 20mA
MAX1584/MAX1585 (PARTIAL)
IN SHDN GND
OUT
Figure 8. Regulated -7.5V Negative CCD Bias Provided by Conventional Inverter (MAX1585 Only)
+1.25V L1 10H TO VBATT 1F
FB_
D2 C2 1F
VOUT+ +15V 20mA R1 1M
MAX1616
NOTE: THIS CIRCUIT CAN OPERATE WITH AUX1 OR AUX2 ON THE MAX1584, AND WITH AUX1 ON THE MAX1585.
AUX_ PWM PVSU
FB_ R2 90.9k D3 VOUT-15V C3 10mA 1F
Q1 DL_
C1 1F D1
Figure 10. +15V and -7.5V CCD Bias Without Transformer from AUX-Driven Boost and Charge Pump. A positive linear regulator (MAX1616) regulates the negative output of the charge pump.
MAX1584 MAX1585 (PARTIAL)
NOTE: THIS CIRCUIT CAN OPERATE WITH AUX1 OR AUX2 ON THE MAX1584, AND WITH AUX1 ON THE MAX1585.
INPUT 1-CELL Li+ VSU L1 PV PVSU DL_ C2 Q1 FB_ R2 R1 L2 D1 OUTPUT 3.3V
Figure 9. 15V Output from AUX-Driven Boost with ChargePump Inversion
PART OF MAX1584 MAX1585 (PARTIAL)
Adding a MAX1801 Slave
The MAX1801 is a 6-pin SOT slave DC-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 MAX1584/MAX1585 (Figure 12).
NOTE: THIS CIRCUIT CAN OPERATE WITH AUX1 OR AUX2 ON THE MAX1584, AND WITH AUX1 ON THE MAX1585.
Figure 11. SEPIC Converter for Additional Boost-Buck Channel 26 ______________________________________________________________________________________
5-Channel Slim DSC Power Supplies MAX1584/MAX1585
TO BATT
TO VBATT
VOUT DL IN
PVSU
MAX1801 OSC
FB COMP GND REF DCON
MAX1584 MAX1585 OSC (PARTIAL)
REF
MAX1584 MAX1585 (PARTIAL)
PVSU AUX1 PWM DL1 D6 15V 100mA
FB1 AUX1OK
Figure 12. Adding a PWM Channel with an External MAX1801 Slave Controller
CURRENTMODE STEP-UP PWM
PV PVSU TO VBATT LXSU L2
GATED +5V TO CCD VSU +5V
MAX1584/MAX1585 (PARTIAL)
AUX3 V-MODE STEP-DOWN PWM DL3
TO PVSU
PGSU FBSU
3.3V LOGIC
FB3 ON3 SDOK TO VBATT OR PVSU
Figure 14. AUX1OK drives an external PFET that switches 5V to the CCD only after the +15V CCD bias supply is in regulation.
Selection section also apply to add-on MAX1801 slave controllers. For more details, refer to the MAX1801 data sheet. Using SDOK and AUX1OK for Power Sequencing The SDOK goes low when the step-down reaches regulation. Some microcontrollers with low-voltage cores require the high-voltage (3.3V) I/O rail not be powered up until the core has a valid supply. The circuit in Figure 13 accomplishes this by driving the gate of a PFET connected between the 3.3V output and the processor I/O supply. Figure 14 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
27
PVSD
TO VBATT OR PVSU
CURRENTMODE STEP-DOWN PWM
LXSD
+1.5V
PGSD
Figure 13. Using SDOK to Gate 3.3V Power to CPU After the Core Voltage Is in Regulation
The MAX1801 controller operation and design are similar to that of the MAX1584/MAX1585 AUX controllers. All comments in the AUX Controller Component
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5-Channel Slim DSC Power Supplies MAX1584/MAX1585
VSU 3.3V
PVSU PV
MAX1584 MAX1585 (PARTIAL)
PV PVSU TO VBATT VSU +5V
MAX1584 MAX1585 (PARTIAL)
PVSD 10F
CURRENT-MODE STEP-UP PWM
LXSU
L2
CURRENT-MODE STEP-DOWN
LXSD
4.7H 22F
VSD 0.8V
PGSU FBSD SCF OK PWR-ON OR FAULT
PGSD FBSD R3 100k VFBSD 1.25V R1 56k
R2 100k
Figure 15. SCF controls a PFET load switch to disconnect all 5V loads on fault. This also allows full-load startup.
Figure 16. Setting PVSD for Outputs Below 1.25V
event of an overload. Or, it can remove the load until the supply reaches regulation, effectively allowing fullload startup. Figure 15 shows such a connection for the step-up output.
spreadsheet and test estimated resistor values. A good starting point is with 100k at R2 and R3.
Designing a PC Board
Good PC board layout is important to achieve optimal performance from the MAX1584/MAX1585. 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 MAX1584/MAX1585 evaluation kit data sheet for a full PC board example.
Setting SDOUT 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 output is a convenient voltage for this) as shown in Figure 16. The equation governing output voltage in Figure 16'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 16, 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
28
Chip Information
TRANSISTOR COUNT: 8234 PROCESS: BiCMOS
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5-Channel Slim DSC 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.)
MAX1584/MAX1585
0.15 C A
D2
C L
D
b D2/2
0.10 M C A B
PIN # 1 I.D.
D/2
0.15 C B
k
PIN # 1 I.D. 0.35x45
E/2 E2/2 E (NE-1) X e
C L
E2
k L
DETAIL A
e (ND-1) X e
C L
C L
L
L
e 0.10 C A 0.08 C
e
C
A1 A3
PROPRIETARY INFORMATION TITLE:
PACKAGE OUTLINE 16, 20, 28, 32L, QFN THIN, 5x5x0.8 mm
APPROVAL DOCUMENT CONTROL NO. REV.
21-0140
C
1 2
COMMON DIMENSIONS
EXPOSED PAD VARIATIONS
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. 9. DRAWING CONFORMS TO JEDEC MO220. 10. WARPAGE SHALL NOT EXCEED 0.10 mm.
PROPRIETARY INFORMATION TITLE:
PACKAGE OUTLINE 16, 20, 28, 32L, QFN THIN, 5x5x0.8 mm
APPROVAL DOCUMENT CONTROL NO. REV.
21-0140
C
2 2
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 ____________________ 29 (c) 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
QFN THIN.EPS

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