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19-3503; Rev 2; 2/06
KIT ATION EVALU ILABLE AVA
2.2MHz, Dual-Output Buck or Boost Converter with POR and Power-Fail Output
General Description Features
4.5V to 5.5V or 5.5V to 23V Input Supply Voltage Range 0.8V (Buck) to 28V (Boost) Output Voltage Two Independent Output DC-DC Converters with Internal Power MOSFETs Each Output can be Configured in Buck or Boost Mode IOUT1 and IOUT2 of 2A and 1A (Respectively) in Buck Mode 180 Out-of-Phase Operation Clock Output for Four-Phase Operation Switching Frequency Programmable from 200kHz to 2.2MHz Digital Soft-Start and Independent Converter Shutdown SYNC Input, Power-On Reset, Manual Reset, And Power-Fail Output Short-Circuit Protection (Buck)/Maximum DutyCycle Limit (Boost) Thermal Shutdown Thermally Enhanced 32-Pin Thin QFN Package Dissipates up to 2.7W at +70C
MAX5072
The MAX5072 is a dual-output DC-DC converter with integrated high-side n-channel power MOSFETs. Each output can be configured either as a buck converter or a boost converter. The MAX5072 is designed to manage the power requirements of xDSL modems. The wide 5.5V to 23V input voltage range allows for the use of inexpensive AC adapters to power the device in xDSL modem applications. Each output is programmable down to 0.8V in the buck mode and up to 28V in the boost mode with an output voltage accuracy of 1%. In the buck mode, converter 1 and converter 2 can deliver 2A and 1A, respectively. The output switching frequency of each converter can be programmed from 200kHz to 2.2MHz to avoid harmonics in the xDSL frequency band of operation. Each output operates 180 out-of-phase, thus reducing input-capacitor ripple current, size, and cost. A SYNC input facilitates external frequency synchronization. Moreover, a CLKOUT output provides out-of-phase clock signal with respect to converter 2, allowing four-phase operation using two MAX5072 ICs in master-slave configuration. The MAX5072 includes an internal digital soft-start that reduces inrush current, eliminates output-voltage overshoot, and ensures monotonic rise in output voltage during power-up. The device includes a power-good output and power-on reset as well as manual reset. In addition, each converter output can be shut down individually. The MAX5072 features a "dying gasp" output, which goes low when the input voltage drops below a preprogrammed voltage. Protection features include output short-circuit protection for buck mode and maximum duty-cycle limit for boost operation, as well as thermal shutdown. The MAX5072 is available in a thermally enhanced 32-pin thin QFN package that can dissipate 2.7W at +70C ambient temperature. The device is rated for operation over the -40C to +85C extended, or -40C to +125C automotive temperature range.
Pin Configuration
BST1/VDD1 DRAIN1 FSEL1
EN1
24
PGOOD1 SOURCE1 SOURCE1 PGND SGND
23
22
21
20
19
18
17 16 15 14 13
MR BYPASS VL VL V+ OSC PFI SYNC
25 26 27 28 29 30 31 32 1
CLKOUT
Applications
xDSL Modems xDSL Routers Point-of-Load DC-DC Converters
MAX5072
RST
TOP VIEW
DRAIN1
COMP1
FB1
12 11 10 9
Ordering Information
PART MAX5072ETJ TEMP RANGE -40C to +85C PIN-PACKAGE PKG CODE
PGND SOURCE2 SOURCE2
32 Thin QFN-EP* T3255-4 (5mm x 5mm)
2
BST2/VDD2
3
DRAIN2
4
DRAIN2
5
EN2
6
FB2
7
COMP2
8
PFO
*EP = Exposed pad. Ordering Information continued at end of data sheet.
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.
2.2MHz, Dual-Output Buck or Boost Converter with POR and Power-Fail Output MAX5072
ABSOLUTE MAXIMUM RATINGS
V+ to PGND............................................................-0.3V to +25V SGND to PGND .....................................................-0.3V to +0.3V VL to SGND...................-0.3V to the lower of +6V or (V+ + 0.3V) BST1/VDD1, BST2/VDD2, DRAIN_, PFO, RST, PGOOD1 to SGND .................................................................-0.3V to +30V BST1/VDD1 to SOURCE1, BST2/VDD2 to SOURCE2 ....................................-0.3V to +6V SOURCE_ to SGND................................................-0.6V to +25V EN_ to SGND ................................................-0.3V to (VL + 0.3V) CLKOUT, BYPASS, OSC, FSEL1, COMP1, COMP2, PFI, MR, SYNC, FB_ to SGND....-0.3V to (VL + 0.3V) SOURCE1, DRAIN1 Peak Current ..............................5A for 1ms SOURCE2, DRAIN2 Peak Current ..............................3A for 1ms VL, BYPASS to SGND Short Circuit............................Continuous Continuous Power Dissipation (TA = +70C) 32-Pin Thin QFN (derate 21.3mW/C above +70C).....2758mW* Package Junction-to-Case Thermal Resistance (JC).......2C/W Operating Temperature Ranges: MAX5072ETJ (TMIN to TMAX)...........................-40C to +85C MAX5072ATJ (TMIN to TMAX).........................-40C to +125C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C *As per JEDEC51 standard.
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
(V+ = VL = 5.2V or V+ = 5.5V to 23V, EN_ = VL, SYNC = GND, IVL = 0, PGND = SGND, CBYPASS = 0.22F, CVL = 4.7F (ceramic), ROSC = 10k (circuit of Figure 1), TA = TJ = TMIN to TMAX, unless otherwise noted.) (Note 1)
PARAMETER SYSTEM SPECIFICATIONS Input Voltage Range Operating Supply Current V+ IQ (Note 2) VL = V+ VL unloaded, no switching, VFB_ = 1V, V+ = 12V, ROSC = 60k EN_ = 0, MR, PFO, and PGOOD_ floating, V+ = 12V, ROSC = 60k (MAX5072ETJ) EN_ = 0, MR, PFO, and PGOOD_ floating, V+ = 12V, ROSC = 60k (MAX5072ATJ) VOUT1 = 3.3V at 1.5A, VOUT2 = 2.5V at 0.75A (fSW = 1.25MHz) V+ = VL = 5V V+ = 12V V+ = 16V 5.5 4.5 2.2 0.6 0.6 82 80 78 % 23 5.5 1.2 1.4 mA 1.4 V mA SYMBOL CONDITIONS MIN TYP MAX UNITS
V+ Standby Supply Current
ISTBY
Efficiency STARTUP/VL REGULATOR VL Undervoltage Lockout Trip Level VL Undervoltage Lockout Hysteresis VL Output Voltage BYPASS OUTPUT BYPASS Voltage BYPASS Load Regulation SOFT-START Digital Ramp Period Soft-Start Steps
UVLO
VL falling
3.95
4.1 175
4.25
V mV
VL
V+ = 5.5V to 23V, ISOURCE = 0 to 40mA IBYPASS = 0, ROSC = 60k (MAX5072ETJ) IBYPASS = 0, ROSC = 60k (MAX5072ATJ) 0 IBYPASS 50A, ROSC = 60k
4.9 1.98 1.975 0
5.2 2.00 2.00 2
5.5 2.02 2.025 10
V
VBYPASS VBYPASS
V mV fOSC clock cycles steps
Internal 6-bit DAC
2048 64
2
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2.2MHz, Dual-Output Buck or Boost Converter with POR and Power-Fail Output
ELECTRICAL CHARACTERISTICS (continued)
(V+ = VL = 5.2V or V+ = 5.5V to 23V, EN_ = VL, SYNC = GND, IVL = 0, PGND = SGND, CBYPASS = 0.22F, CVL = 4.7F (ceramic), ROSC = 10k (circuit of Figure 1), TA = TJ = TMIN to TMAX, unless otherwise noted.) (Note 1)
PARAMETER VOLTAGE-ERROR AMPLIFIER FB_ Input Bias Current FB_ Input Voltage Set Point IFB 0C TA +70C -40C TA +85C -40C TJ +125C (MAX5072ATJ only) 0C to +85C FB_ to COMP_ Transconductance INTERNAL MOSFETS ISWITCH = 100mA, VBST1/VDD1 to VSOURCE1 = 5.2V (MAX5072ETJ) ISWITCH = 100mA, VBST1/VDD1 to VSOURCE1 = 5.2V (MAX5072ATJ) RON1 ISWITCH = 100mA, VBST1/VDD1 to VSOURCE1 = 4.5V (MAX5072ETJ) ISWITCH = 100mA, VBST1/VDD1 to VSOURCE1 = 4.5V (MAX5072ATJ) ISWITCH = 100mA, VBST2/VDD2 to VSOURCE2 = 5.2V ISWITCH = 100mA, VBST2/VDD2 to VSOURCE2 = 4.5V VOUT1 = 3.3V, V+ = 12V (Note 3) VOUT2 = 2.5V, V+ = 12V (Note 3) EN1 = 0V, VDS = 23V EN2 = 0V, VDS = 23V 195 290 gM -40C to +85C -40C to +125C (MAX5072ATJ only) 0.792 0.788 0.788 1.25 1.2 1.2 0.8 0.8 0.8 2.00 2.0 2.0 250 0.808 0.812 0.812 2.70 2.9 2.9 mS V nA SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX5072
195
330 m
On-Resistance Converter 1
200
315
200
350
330 350 2 1
630 m 690 A A 10 10 A A
On-Resistance Converter 2
RON2
Minimum Converter 1 Output Current Minimum Converter 2 Output Current Converter 1 MOSFET Leakage Current Converter 2 MOSFET Leakage Current
IOUT1 IOUT2 ILK1 ILK2
INTERNAL SWITCH CURRENT LIMIT Current-Limit Converter 1 Current-Limit Converter 2 ICL1 ICL2 V+ = 12V (MAX5072ETJ) V+ = 12V (MAX5072ATJ) MAX5072ETJ MAX5072ATJ 2.3 2.3 1.38 1.38 3 3 1.8 1.8 4.3 4.6 2.10 2.10 A A
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3
2.2MHz, Dual-Output Buck or Boost Converter with POR and Power-Fail Output MAX5072
ELECTRICAL CHARACTERISTICS (continued)
(V+ = VL = 5.2V or V+ = 5.5V to 23V, EN_ = VL, SYNC = GND, IVL = 0, PGND = SGND, CBYPASS = 0.22F, CVL = 4.7F (ceramic), ROSC = 10k (circuit of Figure 1), TA = TJ = TMIN to TMAX, unless otherwise noted.) (Note 1)
PARAMETER INTERNAL OSCILLATOR/SYNC Maximum Duty Cycle Switching Frequency Range Switching Frequency Switching Frequency Accuracy SYNC Frequency Range SYNC High Threshold SYNC Low Threshold SYNC Input MIN Pulse Width Clock Output Phase Delay SYNC to SOURCE 1 Phase Delay Clock Output High Level Clock Output Low Level FSEL1 FSEL1 Input High Threshold FSEL1 Input Low Threshold EN_ INPUTS EN_ Input High Threshold EN_ Input Low Threshold EN_ Bias Current MR Minimum Pulse Width MR Glitch Immunity MR to RST Propagation Delay MR Input High Threshold MR Input Low Threshold MR Internal Pullup Resistor Power-On-Reset Threshold FB_ to RST Propagation Delay RST Active Timeout Period RST Output Voltage RST Output Leakage Current tMD VIH VIL RMR VTH tFD tRP VRST_ IRSTLK ISINK = 3mA (MAX5072ETJ) ISINK = 3mA (MAX5072ATJ) V+ = VL = 5.2V, VRST = 23V, VFB_ = 0.8V VIH VIL IB(EN) tMR Maximum glitch pulse width allowed for RST to remain high V+ = VL = +5.2V V+ = VL = +5.2V RST goes high 180ms after VOUT1 and VOUT2 cross this threshold FB overdrive from 0.8V to 0.6V 140 2.4 0.8 44 90 92.5 1.1 200 360 0.4 0.52 1 95 100 1 V+ = VL = +5.2V V+ = VL = +5.2V 2.4 1.8 1.2 0.8 250 10 V V nA s ns s V V k % VOUT s ms V A fSYNC VSYNCH VSYNCL tSYNCIN CLKOUT PHASE VCLKOUTH VCLKOUTL VIH VIL ROSC = 60k, 1%, with respect to converter 2/SOURCE2 waveform VL = 5.2V, sourcing 5mA VL = 5.2V, sinking 5mA V+ = VL = +5.2V V+ = VL = +5.2V 2.4 0.8 4 0.4 100 45 45 DMAX fSW fSET SYNC = SGND, fSW = 1.25MHz SYNC = SGND, fSW = 2.2MHz Each converter ROSC = 10k, each converter 5.6k ROSC 56k, 1%, each converter SYNC input frequency is twice the individual converter frequency 84 84 200 1125 -15 400 2.4 0.8 1250 86 86 95 95 2200 1375 +15 4400 % kHz kHz % kHz V V ns degrees degrees V V V V SYMBOL CONDITIONS MIN TYP MAX UNITS
SYNCPHASE ROSC = 60k, 1%
MANUAL RESET (MR) AND POWER-ON-RESET (RST)
4
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2.2MHz, Dual-Output Buck or Boost Converter with POR and Power-Fail Output
ELECTRICAL CHARACTERISTICS (continued)
(V+ = VL = 5.2V or V+ = 5.5V to 23V, EN_ = VL, SYNC = GND, IVL = 0, PGND = SGND, CBYPASS = 0.22F, CVL = 4.7F (ceramic), ROSC = 10k (circuit of Figure 1), TA = TJ = TMIN to TMAX, unless otherwise noted.) (Note 1)
PARAMETER SYMBOL CONDITIONS PGOOD1 goes high after VOUT crosses PGOOD1 threshold ISINK = 3mA (MAX5072ETJ) ISINK = 3mA (MAX5072ATJ) V+ = VL = 5.2V, VPGOOD1 = 23V, VFB1 = 1V PFI falling VPFI = 0.75V 100mV overdrive tPFD VPFO ILKPFO TSHDN THYST 50mV overdrive ISINK = 3mA (MAX5072ETJ) ISINK = 3mA (MAX5072ATJ) V+ = VL = 5.2V, VPFO = 5.5V, VPFI = 1V Junction temperature Junction temperature +150 30 35 35 0.4 0.52 1 0.76 0.78 20 MIN TYP MAX UNITS POWER-GOOD OUTPUT (PGOOD1) PGOOD1 Threshold PGOOD1 Output Voltage PGOOD1 Output Leakage Current PFI Trip Level PFI Hysteresis PFI Input Bias Current PFI Glitch Immunity PFI to PFO Propagation Delay PFO Output Low Voltage PFO Output Leakage Current THERMAL MANAGEMENT Thermal Shutdown Thermal Hysteresis
PGOOD1VTH
MAX5072
90
92.5
95 0.4 0.52 1 0.80 500
% VOUT V A V mV nA s s V A C C
VPGOOD1 ILKPGOOD1 VTH VTHH IB(PFI)
DYING GASP POWER-FAIL INPUT (PFI), POWER-FAIL OUTPUT (PFO)
Note 1: Specifications at -40C are guaranteed by design and not production tested. Note 2: Operating supply range (V+) is guaranteed by VL line regulation test. Connect V+ to VL for 5V operation. Note 3: Output current may be limited by the power dissipation of the package, see the Power Dissipation section in the Applications Information.
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5
2.2MHz, Dual-Output Buck or Boost Converter with POR and Power-Fail Output MAX5072
Typical Operating Characteristics
(V+ = VL = 5.2V, TA = +25C, unless otherwise noted.)
OUTPUT1 EFFICIENCY (BUCK CONVERTER) vs. LOAD CURRENT
MAX5072 toc01
OUTPUT2 EFFICIENCY (BUCK CONVERTER) vs. LOAD CURRENT
MAX5072 toc02
OUTPUT2 EFFICIENCY (BOOST CONVERTER) vs. LOAD CURRENT
90 80 EFFICIENCY (%) 70 60 50 40 30 20 VIN = 3.3V VIN = 5.0V
MAX5072 toc03
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 VOUT = 3.3V fSW = 2.2MHz VIN = 16.0V VIN = 5V
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0.2 0.3 0.4 0.5 0.6 LOAD (A) 0.7 0.8 0.9 VOUT = 2.5V fSW = 2.2MHz VIN = 16.0V VIN = 12.0V VIN = 5V
100
VIN = 12.0V
10 0 1.0 0.02 0.08 LOAD (A)
VOUT = 12V fSW = 2.2MHz 0.14 0.20
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 LOAD (A)
OUTPUT1 VOLTAGE (BUCK CONVERTER) vs. LOAD CURRENT
MAX5072 toc04
OUTPUT2 VOLTAGE (BUCK CONVERTER) vs. LOAD CURRENT
MAX5072 toc05
VL OUTPUT VOLTAGE vs. CONVERTER SWITCHING FREQUENCY
5.45 5.40 5.35 VL (V) 5.30 5.25 5.20 VIN = 23V BOTH CONVERTERS SWITCHING
MAX5072 toc06
3.40
2.60
5.50
OUTPUT1 VOLTAGE (V)
OUTPUT2 VOLTAGE (V)
3.35
2.55
3.30
2.50
5.15 5.10 5.05 VIN = 5.5V
3.25
3.20 0 0.5 1.0 LOAD (A) 1.5 2.0
2.45 0 0.25 0.50 LOAD (A) 0.75 1.00
5.00 0.1 0.6 1.1 1.6 2.1 2.6 SWITCHING FREQUENCY (fSW)(MHz)
VL DROPOUT VOLTAGE vs. EACH CONVERTER SWITCHING FREQUENCY
MAX5072 toc07
EACH CONVERTER SWITCHING FREQUENCY vs. ROSC
MAX5072 toc08
EACH CONVERTER SWITCHING FREQUENCY vs. TEMPERATURE
SWITCHING FREQUENCY (fSW) (MHz)
MAX5072 toc09
0.35 0.30 DROPOUT VOLTAGE (V) 0.25 0.20 0.15 0.10 VIN = 4.5V 0.05 0 0 0.5 1.0 1.5 2.0 VIN = 5V VIN = 5.5V
10 SWITCHING FREQUENCY (fSW) (MHz)
10.00
2.2MHz 1.25MHz 1.00 0.6MHz 0.3MHz
1
0.1 2.5 0 20 40 ROSC (k) 60 80 SWITCHING FREQUENCY (fSW) (MHz)
0.10 -50 0 50 TEMPERATURE (C) 100 150
6
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2.2MHz, Dual-Output Buck or Boost Converter with POR and Power-Fail Output MAX5072
Typical Operating Characteristics (continued)
(V+ = VL = 5.2V, TA = +25C, unless otherwise noted.)
LINE-TRANSIENT RESPONSE (BUCK CONVERTER)
MAX5072 toc10
CONVERTER 1 LOAD-TRANSIENT RESPONSE (BUCK CONVERTER)
MAX5072 toc11
CONVERTER 2 LOAD-TRANSIENT RESPONSE (BUCK CONVERTER)
MAX5072 toc12
VOUT1 = 3.3V AC-COUPLED 400mV/div VIN 5V/div 0V VOUT1 = 3.3V/1.5A AC-COUPLED 200mV/div VOUT2 = 2.5V/0.75A AC-COUPLED 200mV/div 1ms/div 100s/div VOUT1 = 3.3V AC-COUPLED 200mV/div VOUT2 = 2.5V AC-COUPLED 100mV/div
IOUT1 1A/div 0A 100s/div
IOUT2 500mA/div 0A
SOFT-START/SOFT-STOP
MAX5072 toc13
LOAD-TRANSIENT RESPONSE (BOOST CONVERTER)
MAX5072 toc14
ENABLE 5V/div 0V VOUT1 = 3.3V/1A 2V/div 0V VOUT2 = 2.5V/0.5A 2V/div 0V V+ = VL = 5.2V 2ms/div 100s/div
VOUT1 = 3.3V AC-COUPLED 200mV/div VOUT2 = 12V AC-COUPLED 200mV/div
IOUT2 50mA/div 0A
RST ACTIVE TIMEOUT PERIOD
MAX5072 toc15
OUT-OF-PHASE OPERATION
MAX5072 toc16
0V
ENABLE 5V/div
0V
SOURCE 2 5V/div SOURCE 1 5V/div
0V RST 5V/div VOUT1 0V 5V/div VOUT2 2V/div 0V 0V 0V
INPUT RIPPLE AC-COUPLED 20mV/div CLKOUT 5V/div
40ms/div
100ns/div
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7
2.2MHz, Dual-Output Buck or Boost Converter with POR and Power-Fail Output MAX5072
Typical Operating Characteristics (continued)
(V+ = VL = 5.2V, TA = +25C, unless otherwise noted.)
EXTERNAL SYNCHRONIZATION
MAX5072 toc17
V+ STANDBY SUPPLY CURRENT (ISTBY) vs. TEMPERATURE
SYNC 5V/div 0V SOURCE 1 5V/div ISTBY (mA) 0V VOUT1 RIPPLE AC-COUPLED 20mV/div CLKOUT 5V/div 1.4 ROSC = 10k
MAX5072 toc18
1.8
1.0 ROSC = 60k 0.6
0V
0.2 200ns/div -40 -7 26 59 92 125 TEMPERATURE (C)
V+ SWITCHING SUPPLY CURRENT (ISUPPLY) vs. TEMPERATURE
MAX5072 toc19
OUTPUT1 VOLTAGE (BUCK CONVERTER) vs. TEMPERATURE
3.38 3.36 OUTPUT1 VOLTAGE (V) 3.34 3.32 3.30 3.28 3.26 3.24 3.22 50% LOAD NO LOAD
MAX5072 toc20
35 30 fSW = 2.2MHz ISUPPLY (mA) 25 fSW = 1.25MHz 20 fSW = 600kHz 15 fSW = 300kHz 10 5 -40 -7 26 59 92
3.40
3.20 125 -50 0 50 TEMPERATURE (C) 100 150 TEMPERATURE (C)
OUTPUT2 VOLTAGE (BUCK CONVERTER) vs. TEMPERATURE
MAX5072 toc21
OUTPUT LOAD CURRENT LIMIT vs. TEMPERATURE
2.75 OUTPUT CURRENT LIMIT (A) 2.50 OUTPUT1 2.25 2.00 OUTPUT2 1.75 1.50 1.25 VIN = 5.5V fSW = 2.2MHz
MAX5072 toc22
2.60 50% LOAD OUTPUT2 VOLTAGE (V) 2.55 NO LOAD 2.50
3.00
2.45
2.40 -50 0 50 TEMPERATURE (C) 100 150
1.00 -40 -5 30 TEMPERATURE (C) 65 100
8
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2.2MHz, Dual-Output Buck or Boost Converter with POR and Power-Fail Output MAX5072
Typical Operating Characteristics (continued)
(V+ = VL = 5.2V, TA = +25C, unless otherwise noted.)
FOUR-PHASE OPERATION (SEE FIGURE 3)
MAX5072 toc24
MANUAL RESET (MR)
MAX5072 toc23
MR 5V/div RST 5V/div VOUT1 = 3.3V 5V/div VOUT2 = 2.5V 5V/div
0V
SOURCE 1 (MASTER)
SOURCE 2 0V (MASTER) SOURCE 1 (SLAVE) SOURCE 2 (SLAVE)
0V
100ms/div
400ns/div
Pin Description
PIN 1 NAME CLKOUT FUNCTION Clock Output. CLKOUT is 45 phase-shifted with respect to converter 2 (SOURCE2, Figure 3). Connect CLKOUT (master) to the SYNC of a second MAX5072 (slave) for a four-phase converter.
2
Buck Converter Operation--Bootstrap Flying-Capacitor Connection for Converter 2. Connect BST2/VDD2 to an external ceramic capacitor and diode according to the Standard Application Circuit (Figure 1). BST2/VDD2 Boost Converter Operation--Driver Bypass Capacitor Connection. Connect a low-ESR 0.1F ceramic capacitor from BST2/VDD2 to PGND (Figure 9). Connection to Converter 2 Internal MOSFET Drain. Buck converter operation--use the MOSFET as a high-side switch and connect DRAIN2 to the input supply. Boost converter operation--use the MOSFET as a low-side switch and connect DRAIN2 to the inductor and diode junction (Figure 9). Active-High Enable Input for Converter 2. Drive EN2 low to shut down converter 2, drive EN2 high for normal operation. Use EN2 in conjunction with EN1 for supply sequencing. Connect to VL for always-on operation. Feedback Input for Converter 2. Connect FB2 to a resistive divider between converter 2's output and SGND to adjust the output voltage. To set the output voltage below 0.8V, connect FB2 to a resistive voltage-divider from BYPASS to regulator 2's output (Figure 6). See the Setting the Output Voltage section. Compensation Connection for Converter 2. See the Compensation section to compensate converter 2's control loop. Dying Gasp Comparator Output. The PFO open-drain output goes low when PFI falls below the 0.78V reference. External Clock Synchronization Input. Connect SYNC to a 400kHz to 4400kHz clock to synchronize the switching frequency with the system clock. Each converter frequency is one half the frequency applied to SYNC. Connect SYNC to SGND when not used. Dying Gasp Comparator Noninverting Input. Connect a resistor-divider from the input supply to PFI. PFI forces PFO low when VPFI falls below 0.78V. The PFI comparator has a 20mV (typ) hysteresis. This is an uncommitted comparator and can be used for any protection feature such as OVP or POWER-GOOD.
3, 4
DRAIN2
5
EN2
6
FB2
7 8 9
COMP2 PFO SYNC
10
PFI
_______________________________________________________________________________________
9
2.2MHz, Dual-Output Buck or Boost Converter with POR and Power-Fail Output MAX5072
Pin Description (continued)
PIN NAME FUNCTION Oscillator Frequency Set Input. Connect a resistor from OSC to SGND (ROSC) to set the switching frequency (see the Oscillator section). Set ROSC for equal to or lower oscillator frequency than the SYNC input frequency when using external synchronization (0.2fSYNC < fOSC < 1.2fSYNC). ROSC is still required when an external clock is connected to the SYNC input. Input Supply Voltage. V+ voltage range from 5.5V to 23V. Connect the V+ and VL together for 4.5V to 5.5V input operation. Bypass with a minimum 0.1F ceramic capacitor to SGND. Internal 5.2V Linear Regulator Output. Use VL to drive the high-side switch at BST1/VDD1 and BST2/VDD2. Bypass VL with a 0.1F capacitor to PGND and a 4.7F ceramic capacitor to SGND. 2.0V Output. Bypass to SGND with a 0.22F or greater ceramic capacitor. Active-Low Manual Reset Input. Drive MR low to initiate a reset. RST remains asserted while MR is low and for 180ms (tRP) after MR returns high. MR requires no external debounce circuitry. MR is internally pulled high by a 44k resistor and can be left open if not used. Open-Drain Reset Output. RST remains low when either output voltage is below 92.5% of its regulation point or while MR is low. After soft-start is completed and both outputs exceed 92.5% of their nominal output voltage, RST becomes high impedance after a 180ms (typ) delay. RST remains high impedance as long as both outputs maintain regulation. Compensation Connection for Converter 1 (See the Compensation Section) Feedback Input for Converter 1. Connect FB1 to a resistive divider between converter 1's output and SGND to program the output voltage. To set the output voltage below 0.8V, connect FB1 to a resistive voltagedivider from BYPASS to regulator 1's output (Figure 6). See the Setting the Output Voltage section. Active-High Enable Input for Converter 1. Drive EN1 low to shut down converter 1, drive EN1 high for normal operation. Use EN1 in conjunction with EN2 for supply sequencing. Connect to VL for always-on operation. Connection to the Converter 1 Internal MOSFET Drain. Buck converter operation--use the MOSFET as a high-side switch and connect DRAIN1 to the input supply. Boost converter operation--use the MOSFET as a low-side switch and connect DRAIN1 to the inductor and diode junction.
11
OSC
12 13, 14 15 16
V+ VL BYPASS MR
17
RST
18 19
COMP1 FB1
20
EN1
21, 22
DRAIN1
23
Buck Converter Operation--Bootstrap Flying-Capacitor Connection for Converter 1. Connect BST1/VDD1 to an external ceramic capacitor and diode according to the Standard Application Circuit (Figure 1). BST1/VDD1 Boost Converter Operation--Driver Bypass Capacitor Connection. Connect a low-ESR 0.1F ceramic capacitor from BST1/VDD1 to PGND (Figure 9). Converter 1 Frequency Select Input. Connect FSEL1 to VL for normal operation. Connect FSEL1 to SGND to reduce converter 1's switching frequency to 1/2 converter 2's switching frequency (converter 1 switching frequency will be 1/4 the SYNC frequency). Do not leave FSEL1 unconnected. Converter 1 Power-Good Output. Open-drain output goes low when converter 1's output falls below 92.5% of its set regulation voltage. Use PGOOD1 and EN2 to sequence the converters. Connection to the Converter 1 Internal MOSFET Source. Buck Converter Operation--connect SOURCE1 to the switched side of the inductor as shown in Figure 1. Boost Converter Operation--connect SOURCE1 to PGND.
24
FSEL1
25
PGOOD1
26, 27
SOURCE1
10
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2.2MHz, Dual-Output Buck or Boost Converter with POR and Power-Fail Output
Pin Description (continued)
PIN 28, 30 29 31, 32 EP NAME PGND SGND SOURCE2 SGND FUNCTION Power Ground. Connect rectifier diode anode, input capacitor negative, output capacitor negative, and VL bypass capacitor returns to PGND. Signal Ground. Connect SGND to the exposed pad. Connect SGND and PGND together at a single point. Connection to the Converter 2 Internal MOSFET Source. Buck Converter Operation--connect SOURCE2 to the switched side of the inductor as shown in Figure 1. Boost Converter Operation--connect SOURCE2 to PGND (Figure 9). Exposed Paddle. Connect to SGND. Solder EP to the SGND plane for better thermal performance.
MAX5072
PGOOD1 OUTPUT 2.5V/1A VL OUTPUT 3.3V/2A
32
VL CLOCK OUT
31
30
29
28
27
26
25
VL
SOURCE2 PGND SGND PGND SOURCE1 PGOOD1 FSEL1 24 1 CLKOUT
2 BST2/VDD2 3 DRAIN2 4 DRAIN2
ON OFF
EP
SGND
BST1/VDD1 23 DRAIN1 22 DRAIN1 21
5 EN2 6 FB2 7 COMP2
MAX5072
EN1 20 FB1 19 COMP1 18 RST 17 VL BYPASS MR 14 15 16 VOUT1
ON OFF
VL PFO DYING GASP SGND
8 PFO SYNC PFI 9 10
SYSTEM CLOCK
OSC 11
V+ 12
VL 13
P RESET INPUT
MANUAL RESET
VIN = 5.5V TO 23V
PGND
SGND*
*CONNECT PGND AND SGND TOGETHER AT ONE POINT NEAR THE RETURN TERMINALS OF THE V+ AND VL BYPASS CAPACITORS.
Figure 1. MAX5072 Dual Buck Regulator Application Circuit
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11
2.2MHz, Dual-Output Buck or Boost Converter with POR and Power-Fail Output MAX5072
Detailed Description
PWM Controller
The MAX5072 converter uses a pulse-width modulation (PWM) voltage-mode control scheme for each out-ofphase controller. It is nonsynchronous rectification and uses an external low-forward-drop Schottky diode for rectification. The controller generates the clock signal by dividing down the internal oscillator or the SYNC input when driven by an external clock, so each controller's switching frequency equals half the oscillator frequency (fSW = fOSC / 2). An internal transconductance error amplifier produces an integrated error voltage at the COMP pin, providing high DC accuracy. The voltage at COMP sets the duty cycle using a PWM comparator and a ramp generator. At each rising edge of the clock, converter 1's high-side n-channel MOSFET turns on and remains on until either the appropriate or maximum duty cycle is reached, or the maximum current limit for the switch is detected. Converter 2 operates out-of-phase, so the second high-side MOSFET turns on at each falling edge of the clock. In the case of buck operation (Figure 1), during each high-side MOSFET's on-time, the associated inductor current ramps up. During the second half of the switching cycle, the high-side MOSFET turns off and forward biases the Schottky rectifier. During this time, the SOURCE voltage is clamped to 0.4V (V D ) below ground. The inductor releases the stored energy as its current ramps down, and provides current to the output. The bootstrap capacitor is also recharged from the inductance energy when the MOSFET turns off. The circuit goes in discontinuous conduction mode operation at light load, when the inductor current completely discharges before the next cycle commences. Under overload conditions, when the inductor current exceeds the peak current limit of the respective switch, the highside MOSFET turns off quickly and waits until the next clock cycle. In the case of boost operation, the MOSFET is a lowside switch (Figure 9). During each on-time, the inductor current ramps up. During the second half of the switching cycle, the low-side switch turns off and forward biases the Schottky diode. During this time the DRAIN voltage is clamped to 0.4V (VD) above VOUT_ and the inductor provides energy to the output as well as replenishes the output capacitor charge. ROSC = 25 x 109 fOSC
where fOSC is the internal oscillator frequency in hertz and ROSC in ohms. The two independent regulators in the MAX5072 switch 180 out-of-phase to reduce input filtering requirements, to reduce electromagnetic interference (EMI), and to improve efficiency. This effectively lowers component cost and saves board space, making the MAX5072 ideal for cost-sensitive applications. With dual synchronized out-of-phase operation, the MAX5072's high-side MOSFETs turn on 180 out-ofphase. The instantaneous input current peaks of both regulators do not overlap, resulting in reduced RMS ripple current and input voltage ripple. This reduces the required input capacitor ripple current rating, allows for fewer or less expensive capacitors, and reduces shielding requirements for EMI. The out-of-phase waveforms in the Typical Operating Characteristics demonstrate synchronized 180 out-of-phase operation.
Synchronization (SYNC)/Clock Output (CLKOUT)
The main oscillator can be synchronized to the system clock by applying an external clock (fSYNC) at SYNC. The fSYNC frequency must be twice the required operating frequency of an individual converter. Use a TTL logic signal for the external clock with at least a 100ns pulse width. ROSC is still required when using external synchronization. Program the internal oscillator frequency so 0.2f SYNC < f OSC < 1.2f SYNC . The rising edge of fSYNC synchronizes the turn-on edge of internal MOSFET (see Figure 3). ROSC = 25 x 109 fOSC
Internal Oscillator/Out-of-Phase Operation
The internal oscillator generates the 180 out-of-phase clock signal required by each regulator. The internal oscillator frequency is programmable from 400kHz to 4.4MHz using a single 1% resistor at ROSC. Use the following equation to calculate ROSC:
12
where fOSC is the internal oscillator frequency in hertz and ROSC in ohms, fOSC = 2 x fSW. Two MAX5072s can be connected in master-slave configuration for four ripple-phase operation. The MAX5072 provides a clock output (CLKOUT) that is 45 phaseshifted with respect to the internal switch turn-on edge. Feed the CLKOUT of the master to the SYNC input of the slave. The effective input ripple switching frequency shall be four times the individual converter's switching frequency. When driving the master converter using external clock at SYNC, set the clock duty cycle to 50% for a 90 phase-shifted operation.
______________________________________________________________________________________
2.2MHz, Dual-Output Buck or Boost Converter with POR and Power-Fail Output MAX5072
V+
MAX5072
CONVERTER 1
LDO
VL
VL
DEAD-TIME CONTROL OSCILLATOR FREQUENCY FOLDBACK Q N Q
BST1/VDD1
DRAIN1
BYPASS
SOURCE1
F_SEL1
FREQUENCY DIVIDER
Q VREF fSW/4 PGOOD1
VREF EN1 DIGITAL SOFT-START FB1 COMP1 VCC
0.5VREF
0.92VREF VCC MAIN OSCILLATOR VCC RESET
SYNC CKO OSC
MR
DEBOUNCE OPEN DRAIN
180mS DELAY VREF
PFI
35S GLITCH IMMUNITY VL RESET2 OSCILLATOR CONVERTER 2
PFO BST2/VDD2 DRAIN2
VDD2 SOURCE2 FB2 COMP2
EN2
Figure 2. Functional Diagram ______________________________________________________________________________________ 13
2.2MHz, Dual-Output Buck or Boost Converter with POR and Power-Fail Output MAX5072
VIN CIN V+ OUTPUT2 DRAIN2 SOURCE2 DRAIN1 SOURCE1 OUTPUT1 OUTPUT4 DRAIN2 SOURCE2 V+ DRAIN1 SOURCE1 OUTPUT3
DUTY CYCLE = 50% CLKIN SYNC CLKOUT MASTER SYNC SLAVE
SYNC
CLKOUT (MASTER)
CLKOUT (SLAVE)
SOURCE1 (MASTER) SYNCPHASE SOURCE2 (MASTER) CLKOUTPHASE
SOURCE1 (SLAVE)
SOURCE2 (SLAVE)
CIN (RIPPLE)
Figure 3. Synchronized Controllers
Frequency Select (FSEL1)
Sometimes it is necessary to operate the converter at a lower switching frequency to keep the losses low for lower power dissipation. However, it is not possible to have different frequencies for two converters operating out-of-phase. Also, frequency beating may occur if the individual converter frequencies are not selected carefully. To avoid these issues, and still achieve the lower
power dissipation in the package, the MAX5072 provides a frequency select (FSEL1) pin. Connecting FSEL1 to ground reduces the switching frequency of converter 1 to 1/2 the switching frequency of converter 2 and 1/4th of the internal oscillator switching frequency. In this case, the input capacitor ripple frequency is 1.5 times the converter 2 switching frequency and also has unsymmetrical ripple waveform.
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2.2MHz, Dual-Output Buck or Boost Converter with POR and Power-Fail Output
Input Voltage (V+)/Internal Linear Regulator (VL)
All internal control circuitry operates from an internally regulated nominal voltage of 5.2V (VL). At higher input voltages (V+) of 5.5V to 23V, VL is regulated to 5.2V. At 5.5V or below, the internal linear regulator operates in dropout mode, where VL follows V+. Depending on the load on VL, the dropout voltage can be high enough to reduce VL below the undervoltage lockout (UVLO) threshold. For input voltages of less than 5.5V, connect V+ and VL together. The load on VL is proportional to the switching frequency of converter 1 and converter 2. See the VL Dropout Voltage vs. Each Converter Switching Frequency graph in the Typical Operating Characteristics. For input voltage ranges higher than 5.5V, use the internal regulator. Bypass V+ to SGND with a low-ESR, 0.1F or greater ceramic capacitor placed close to the MAX5072. Current spikes from VL may disturb internal circuitry powered by VL. Bypass VL with a low-ESR, ceramic 0.1F capacitor to PGND and a 4.7F capacitor to SGND.
Enable
The MAX5072 dual converter provides separate enable inputs EN1 and EN2 to individually control or sequence the output voltages. These active-high enable inputs are TTL compatible. Pulling EN_ high ramps up the reference slowly, which provides soft-start at the outputs. Forcing the EN_ low externally disables the individual output and generates a RST signal. Use EN1, EN2, and PGOOD1 for sequencing (see Figure 4). Connect PGOOD1 to EN2 to make sure converter 1's output is within regulation before converter 2 starts. Add an RC network from VL to EN1 and EN2 to delay the individual converter. A larger RC time constant means a more delayed output. Sequencing reduces input inrush current and possible chattering. Connect the EN_ to VL for always-on operation.
MAX5072
MR
Microprocessor-based products require manual reset capability, allowing the operator or external logic circuitry to initiate a reset. A logic low on MR asserts reset. Reset remains asserted while MR is low, and for the Reset Active Timeout Period (tRP) after MR returns high. MR has an internal 44k pullup resistor to VL, so it can be left unconnected if not used. MR can be driven to TTL logic levels. Connect a normally open momentary switch from MR to SGND to create a manual reset function. Note that external debounce circuitry is not required. If MR is driven from long cables or if the device is used in a noisy environment, connect a 0.1F capacitor from MR to SGND to provide additional noise immunity.
Undervoltage Lockout/Soft-Start
The MAX5072 includes an undervoltage lockout with hysteresis and a power-on-reset circuit for smooth converter turn-on and monotonic rise of the output voltage. The rising UVLO threshold is internally set to 4.3V with a 175mV hysteresis. Hysteresis at UVLO eliminates "chattering" during startup. When VL drops below UVLO, the internal switches are turned off and RST is forced low. Digital soft-start/soft-stop is provided internally to reduce input surge currents and glitches at the input during turn-on/turn-off. When UVLO is cleared and EN_ is high, digital soft-start slowly ramps up the internal reference voltage in 64 steps. The total soft-start period is 2048 switching cycles of the internal oscillator. To calculate the soft-start period, use the following equation: t SS = 2048 fOSC
RST Output
RST is an open-drain output. RST pulls low when either output falls below 92.5% of its nominal regulation voltage. Once both outputs exceed 92.5% of their nominal regulated voltages and both soft-start cycles are completed, RST enters a high-impedance state after the 180ms active timeout period. To obtain a logic-voltage output, connect a pullup resistor from RST to a logic supply voltage. The internal open-drain MOSFET can sink 3mA while providing a TTL logic-low signal. If unused, ground RST or leave it unconnected.
PGOOD1
In addition to RST, converter 1 also includes a powergood flag. Pull PGOOD1 to a logic voltage to provide logic-level output. PGOOD1 is an open-drain output and can sink 3mA while providing the TTL logic-low signal. PGOOD1 goes low when converter 1's output drops to 92.5% of its nominal regulated voltage. Connect PGOOD1 to SGND or leave unconnected, if not used.
where fOSC is the internal oscillator frequency in hertz, which is twice the switching frequency of each converter.
______________________________________________________________________________________
15
2.2MHz, Dual-Output Buck or Boost Converter with POR and Power-Fail Output MAX5072
VIN VL VL VIN
OUTPUT2
VL DRAIN2 SOURCE2
V+ DRAIN1 SOURCE1
OUTPUT1
OUTPUT2
VL DRAIN2 SOURCE2
V+ DRAIN1 SOURCE1
OUTPUT1
MAX5072 FB2 VL EN2 FB1 R2 EN1 PGOOD1 VL VL C2 EN2 FB2
MAX5072 FB1 R1 EN1 C1 VL
SEQUENCING--OUTPUT 2 DELAYED WITH RESPECT TO OUTPUT 1.
R1/C1 AND R2/C2 ARE SIZED FOR REQUIRED SEQUENCING.
Figure 4. Power-Supply Sequencing Configurations
Dying Gasp Comparator (PFI/PFO)
The MAX5072 contains an uncommitted comparator with an open-drain output. The inverting input of the comparator is connected to an internal precision 0.78V reference. Connect the noninverting input (PFI) to VIN through a resistor-divider to program the input trip threshold (VTRIP). The power-fail output (PFO) is pulled low when PFI drops below 0.78V. PFI provides 20mV hysteresis to avoid glitches during transition. The PFO signal provides an advance signal to the processor before the converter 1/converter 2 loses regulation. The input trip threshold (VTRIP) can be adjusted to provide advance signaling before the outputs drop to 92.5% of the regulation voltage. The input capacitors hold charge and provide energy to the converter after VIN is disconnected. The hold-up time (tHOLD) is defined as the time when the input voltage drops below VTRIP and the output falls out of regulation at the low end of the input voltage range VIN(MIN) (Figure 5). Use the following equations to calculate the resistor-divider and the C IN required for the proper hold-up time. P P 2 OUT1 + OUT2 2 1
2 V2 TRIP - V IN(MIN)
VL CIN
VIN
OUTPUT2
VL DRAIN2 SOURCE2
V+ DRAIN1 SOURCE1
OUTPUT1
R1 MAX5072 PFI VL R2
PFO
PFO
Figure 5. Dying Gasp Feature Monitors Input Supply V R1 = R2 TRIP - 1 0.78
R2 can be any value from 10k to 100k (Figure 5).
Current Limit
x t HOLD The internal switch current of each converter is sensed using an internal current mirror. Converter 1 and converter 2 have 2A and 1A internal switches. When the peak switch current crosses the current-limit threshold of 3A (typ) and 1.8A (typ) for converter 1 and converter 2, respectively, the on cycle is terminated immediately and the inductor is allowed to discharge. The next cycle resumes at the next clock pulse.
CIN =
where 1 and 2 are efficiencies of the converter 1 and converter 2, respectively.
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2.2MHz, Dual-Output Buck or Boost Converter with POR and Power-Fail Output
In deep overload or short-circuit conditions when the FB voltage drops below 0.4V, the switching frequency is reduced to 1/4 x fSW to provide sufficient time for the inductor to discharge. During overload conditions, if the voltage across the inductor is not high enough to allow for the inductor current to properly discharge, current runaway may occur. Current runaway can destroy the device in spite of internal thermal-overload protection. Reducing the switching frequency during overload conditions prevents current runaway.
MAX5072
LX_ RA FB_ RB MAX5072
BYPASS RC FB_ RA MAX5072 LX_
VOUT_ > 0.8V
VOUT_ < 0.8V
Thermal-Overload Protection
During continuous short circuit or overload at the output, the power dissipation in the IC can exceed its limit. Internal thermal shutdown is provided to avoid irreversible damage to the device. When the die temperature or junction temperature exceeds +150C, an on-chip thermal sensor shuts down the device, forcing the internal switches to turn off, allowing the IC to cool. The thermal sensor turns the part on again after the junction temperature cools by +30C. During thermal shutdown, both regulators shut down, RST goes low, and soft-start resets.
Figure 6. Adjustable Output Voltage
Buck Converter
Effective Input Voltage Range Although the MAX5072 converters can operate from input supplies ranging from 4.5V to 23V, the input voltage range can be effectively limited by the MAX5072 duty-cycle limitations for a given output voltage. The maximum input voltage is limited by the minimum ontime (tON(MIN)): VIN(MAX) VOUT t ON(MIN) x fSW
Applications Information
Setting the Switching Frequency
The controller generates the clock signal by dividing down the internal oscillator or the SYNC input signal when driven by an external oscillator. The switching frequency equals half the oscillator frequency (fSW = fOSC / 2). The internal oscillator frequency is set by a resistor (ROSC) connected from OSC to SGND. The relationship between fSW and ROSC is: 12.5 x 109 ROSC = fSW where fSW and fOSC are in hertz, and ROSC is in ohms. For example, a 1250kHz switching frequency is set with ROSC = 10k. Higher frequencies allow designs with lower inductor values and less output capacitance. Consequently, peak currents and I2R losses are lower at higher switching frequencies, but core losses, gatecharge currents, and switching losses increase. A rising clock edge on SYNC is interpreted as a synchronization input. If the SYNC signal is lost, the internal oscillator takes control of the switching rate, returning the switching frequency to that set by ROSC. This maintains output regulation even with intermittent SYNC signals. When an external synchronization signal is used, ROSC should be set for the oscillator frequency to be lower than or equal to the SYNC rate (fSYNC).
where tON(MIN) is 100ns. The minimum input voltage is limited by the maximum duty cycle (DMAX = 0.88): + VDROP1 V VIN(MIN) = OUT + VDROP2 - VDROP1 0.88 where VDROP1 is the total parasitic voltage drops in the inductor discharge path, which includes the forward voltage drop (VD) of the rectifier, the series resistance of the inductor, and the PC board resistance. VDROP2 is the total resistance in the charging path, which includes the on-resistance of the high-side switch, the series resistance of the inductor, and the PC board resistance. Setting the Output Voltage For 0.8V or greater output voltages, connect a voltagedivider from OUT_ to FB_ to SGND (Figure 6). Select RB (FB_ to SGND resistor) to between 1k and 10k. Calculate RA (OUT_ to FB_ resistor) with the following equation: V RA = RB OUT - 1 VFB where VFB_ = 0.8V (see the Electrical Characteristics table) and VOUT_ can range from VFB_ to 28V (boost operation).
17
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2.2MHz, Dual-Output Buck or Boost Converter with POR and Power-Fail Output MAX5072
For output voltages below 0.8V, set the MAX5072 output voltage by connecting a voltage-divider from the output to FB_ to BYPASS (Figure 6). Select RC (FB to BYPASS resistor) higher than a 50k range. Calculate RA with the following equation: V - VOUT RA = RC FB VBYPASS - VFB where VFB = 0.8V, VBYPASS = 2V (see the Electrical Characteristics table), and VOUT_ can range from 0V to VFB_. Inductor Selection Three key inductor parameters must be specified for operation with the MAX5072: inductance value (L), peak inductor current (IL), and inductor saturation current (ISAT). The minimum required inductance is a function of operating frequency, input-to-output voltage differential and the peak-to-peak inductor current (IL). Higher IL allows for a lower inductor value while a lower I L requires a higher inductor value. A lower inductor value minimizes size and cost, improves large-signal transient response, but reduces efficiency due to higher peak currents and higher peak-to-peak output ripple voltage for the same output capacitor. On the other hand, higher inductance increases efficiency by reducing the ripple current. However, resistive losses due to extra wire turns can exceed the benefit gained from lower ripple current levels, especially when the inductance is increased without also allowing for larger inductor dimensions. A good compromise is to choose IL equal to 30% of the full load current. To calculate the inductance use the following equation: L= VOUT (VIN - VOUT ) VIN x fSW x IL Input Capacitors The discontinuous input current waveform of the buck converter causes large ripple currents at the input. The switching frequency, peak inductor current, and the allowable peak-to-peak voltage ripple dictate the input capacitance requirement. Increasing the switching frequency or the inductor value lowers the peak to average current ratio, yielding a lower input capacitance requirement. Note that two converters of MAX5072 run 180 out-of-phase, thereby effectively doubling the switching frequency at the input. The input ripple waveform would be unsymmetrical due to the difference in load current and duty cycle between converter 1 and converter 2. The input ripple is comprised of VQ (caused by the capacitor discharge) and VESR (caused by the ESR of the capacitor). A higher load converter dictates the ESR requirement, while the capacitance requirement is a function of the loading mismatch between the two converters. The worst-case mismatch is when one converter is at full load while the other is at no load or in shutdown. Use low-ESR ceramic capacitors with high ripple-current capability at the input. Assume the contribution from the ESR and capacitor discharge equal to 50%. Calculate the input capacitance and ESR required for a specified ripple using the following equations: VESR ESRIN = IL IOUT + 2 where IL = and CIN = where V D = OUT VIN where IOUT is the maximum output current from either converter 1 or converter 2, and D is the duty cycle for that converter. fSW is the frequency of each individual converter. For example, at VIN = 12V, VOUT = 3.3V at I OUT = 2A, and with L = 3.3H, the ESR and input capacitance are calculated for a peak-to-peak input IOUT x D(1 - D) VQ x fSW
(VIN - VOUT )
x VOUT
VIN x fSW x L
where VIN and VOUT are typical values (so that efficiency is optimum for typical conditions). The switching frequency is set by R OSC (see the Setting the Switching Frequency section). The peak-to-peak inductor current, which reflects the peak-to-peak output ripple, is worst at the maximum input voltage. See the Output Capacitor Selection section to verify that the worst-case output ripple is acceptable. The inductor saturating current is also important to avoid runaway current during the output overload and continuous short circuit. Select the ISAT to be higher than the maximum peak current limits of 4.5A and 2.2A for converter 1 and converter 2.
18
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2.2MHz, Dual-Output Buck or Boost Converter with POR and Power-Fail Output
ripple of 100mV or less, yielding an ESR and capacitance value of 20m and 6.8F for 1.25MHz frequency. Use a 100F capacitor at low input voltages to avoid possible undershoot below the undervoltage lockout threshold during power-on and transient loading. Output Capacitor Selection The allowable output ripple voltage and the maximum deviation of the output voltage during step load currents determines the output capacitance and its ESR. The output ripple is comprised of VQ (caused by the capacitor discharge) and VESR (caused by the ESR of the capacitor). Use low-ESR ceramic or aluminum electrolytic capacitors at the output. For aluminum electrolytic capacitors, the entire output ripple is contributed by VESR. Use the ESROUT equation to calculate the ESR requirement and choose the capacitor accordingly. If using ceramic capacitors, assume the contribution to the output ripple voltage from the ESR and the capacitor discharge are equal. Calculate the output capacitance and ESR required for a specified ripple using the following equations: ESROUT = VESR IL tronics being powered. When using a ceramic capacitor, assume 80% and 20% contribution from the output capacitance discharge and the ESR drop, respectively. Use the following equations to calculate the required ESR and capacitance value: ESROUT = VESR ISTEP
MAX5072
I x t RESPONSE COUT = STEP VQ where I STEP is the load step and t RESPONSE is the response time of the controller. Controller response time depends on the control-loop bandwidth.
Boost Converter
The MAX5072 can be configured for step-up conversion since the internal MOSFET can be used as a low-side switch. Use the following equations to calculate the inductor (LMIN), input capacitor (CIN), and output capacitor (COUT) when using the converter in boost operation. Inductor Choose the minimum inductor value so the converter remains in continuous mode operation at minimum output current (IOMIN). LMIN = V2IN x D x 2 x fSW x VO x IOMIN
COUT = where
IL 8 x VQ x fSW
VO _ RIPPLE VESR + VQ where IL is the peak-to-peak inductor current as calculated above and fSW is the individual converter's switching frequency. The allowable deviation of the output voltage during fast transient loads also determines the output capacitance and its ESR. The output capacitor supplies the step load current until the controller responds with a greater duty cycle. The response time (tRESPONSE ) depends on the closed-loop bandwidth of the converter. The high switching frequency of MAX5072 allows for higher closed-loop bandwidth, reducing tRESPONSE and the output capacitance requirement. The resistive drop across the output capacitor ESR and the capacitor discharge causes a voltage droop during a step load. Use a combination of low-ESR tantalum and ceramic capacitors for better transient load and ripple/noise performance. Keep the maximum output voltage deviation above the tolerable limits of the elec-
where V + VD - VIN D= O VO + VD - VDS and IOMIN = 0.25 x IO The VD is the forward voltage drop of the external Schottky diode, D is the duty cycle, and VDS is the voltage drop across the internal switch. Select the inductor with low DC resistance and with a saturation current (ISAT) rating higher than the peak switch current limit of 4.5A and 2.2A of converter 1 and converter 2, respectively. Input Capacitor The input current for the boost converter is continuous and the RMS ripple current at the input is low. Calculate the capacitor value and ESR of the input capacitor using the following equations.
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19
2.2MHz, Dual-Output Buck or Boost Converter with POR and Power-Fail Output MAX5072
CIN = IL x D 4 x fSW x VQ VESR IL
VOUT R1 gM
ESR = where IL
COMP
R2
VREF
+ RF CF CCF
(VIN - VDS ) =
xD
Figure 7. Type II Compensation Network.
VOUT CCF RI CI R2 gM VREF + COMP CF
L x fSW
where VDS is the total voltage drop across the internal MOSFET plus the voltage drop across the inductor ESR. IL is the peak-to-peak inductor ripple current as calculated above. VQ is the portion of input ripple due to the capacitor discharge and VESR is the contribution due to ESR of the capacitor. Output Capacitor Selection For the boost converter, the output capacitor supplies the load current when the main switch is ON. The required output capacitance is high, especially at higher duty cycles. Also, the output capacitor ESR needs to be low enough to minimize the voltage drop due to the ESR while supporting the load current. Use the following equation to calculate the output capacitor for a specified output ripple tolerance. VESR ESR = IO I x DMAX COUT = O VQ x fSW IO is the load current, VQ is the portion of the ripple due to the capacitor discharge and VESR is the contribution due to the ESR of the capacitor. DMAX is the maximum duty cycle at minimum input voltage. Power Dissipation The MAX5072 includes a high-frequency, low RDS_ON switching MOSFET. At +85C, the RDS_ON of the internal switch for converter 1 and converter 2 are 290m and 630m, respectively. The DC loss is a function of the RMS current in the switch while the switching loss is a function of switching frequency and input voltage. Use the following equations to calculate the RMS current, DC loss, and switching loss of each converter. The MAX5072 device is available in a thermally enhanced package and can dissipate up to 2.7W at +70C ambi20
R1
RF
Figure 8. Type III Compensation Network
ent temperature. The total power dissipation in the package must be limited so the junction temperature does not exceed its absolute maximum rating of +150C at maximum ambient temperature. For the buck converter: D IRMS = (I2DC +I2PK +(IDC x IPK )) x MAX 3 PDC = I2RMS x RDS(ON)MAX where IDC = IO - IL 2 IL 2
IPK = IO +
See the Electrical Characteristics table for the RDS(ON)MAX value.
______________________________________________________________________________________
2.2MHz, Dual-Output Buck or Boost Converter with POR and Power-Fail Output
PSW = VINMAX x IO x (t R + t F ) x fSW 4 where PDC1 and PDC2 are DC losses in converter 1 and converter 2, respectively. PSW1 and PSW2 are switching losses in converter 1 and converter 2, respectively. Calculate the temperature rise of the die using the following equation: TJ = TC + (PT x J-C) where J-C is the junction-to-case thermal impedance of the package equal to +2C/W. Solder the exposed pad of the package to a large copper area to minimize the case-to-ambient thermal impedance. Measure the temperature of the copper area near the device at a worst-case condition of power dissipation and use +2C/W as J-C thermal impedance. The case-to-ambient thermal impedance (C-A) is dependent on how well the heat is transferred from the PC board to the ambient. Use large copper area to keep the PC board temperature low. The C-A is usually in the +20C/W to +40C/W range.
MAX5072
For the boost converter: D IRMS = (I2DC +I2PK +(IDC x IPK )) x MAX 3 V xI IIN = O O VIN x
IL =
(VIN - VDS ) x D
L x fSW IL 2 IL 2
IDC = IIN -
Compensation
The MAX5072 provides an internal transconductance amplifier with its inverting input and its output available to the user for external frequency compensation. The flexibility of external compensation for each converter offers wide selection of output filtering components, especially the output capacitor. For cost-sensitive applications, use high-ESR aluminum electrolytic capacitors; for component size-sensitive applications, use low-ESR tantalum or ceramic capacitors at the output. The high switching frequency of MAX5072 allows use of ceramic capacitors at the output. Choose all the passive power components that meet the output ripple, component size, and component cost requirements. Choose the small-signal components for the error amplifier to achieve the desired closed-loop bandwidth and phase margin. Use a simple pole-zero pair (Type II) compensation if the output capacitor ESR zero frequency is below the unity-gain crossover frequency (fC). Type III compensation is necessary when the ESR zero frequency is higher than fC or when compensating for a continuous mode boost converter that has a right-half plane zero. Use the following procedure 1 to calculate the compensation network components when fZERO,ESR < fC. Buck Converter Compensation Procedure 1 (see Figure 7): Calculate the fZERO,ESR and LC double pole:
IPK = IIN +
PDC = I2RMS x RDS(ON)MAX where VDS is the drop across the internal MOSFET. See the Electrical Characteristics for the RDS(ON)MAX value. V x I x (t R + t F ) x fSW PSW = O IN 4 where tR and tF are rise and fall times of the internal MOSFET. The tR and tF are typically 20ns, and can be measured in the actual application. The supply current in the MAX5072 is dependent on the switching frequency. See the Typical Operating Characteristics to find the supply current of the MAX5072 at a given operating frequency. The power dissipation (PS) in the device due to supply current (IS) is calculated using following equation. PS = VINMAX x ISUPPLY The total power dissipation PT in the device is: PT = PDC1 + PDC2 + PSW1 + PSW2 + PS
______________________________________________________________________________________
21
2.2MHz, Dual-Output Buck or Boost Converter with POR and Power-Fail Output MAX5072
1 fZERO, ESR = 2 x ESR x COUT 1 fLC = 2 x LOUT x COUT Calculate the unity-gain crossover frequency as: f fC = SW 20 If the fZERO,ESR is lower than fC and close to fLC, use a Type II compensation network where RFCF provides a midband zero fmid,zero, and RFCCF provides a high-frequency pole. Calculate modulator gain GM at the crossover frequency. GM = VIN ESR 0.8 x x VOSC ESR + 2 x fC x LOUT VOUT
where VOSC is a peak-to-peak ramp amplitude equal to 1V.
PGOOD1 VL OUTPUT 3.3V/2A
CLOCK OUT VL
32
31
30
29
28
27
26
25
VL
SOURCE2 PGND SGND PGND SOURCE1 PGOOD1 FSEL1 24 1 CLKOUT
OUTPUT 2.5V/1A
2 BST2/VDD2 EP 3 DRAIN2 4 DRAIN2
ON OFF
SGND BST1/VDD1 23
DRAIN1 22 DRAIN1 21
5 EN2 6 FB2 7 COMP2
MAX5072
EN1 20 FB1 19 COMP1 18
ON OFF
VOUT1 VL PFO DYING GASP SGND P RESET INPUT SYSTEM CLOCK
8 PFO SYNC PFI 9 10
OSC 11
V+ 12
VL 13
RST 17 VL BYPASS MR 14 15 16
MANUAL RESET
VIN = 5.5V TO 23V
PGND
SGND* *CONNECT PGND AND SGND TOGETHER AT ONE POINT NEAR THE RETURN TERMINALS OF THE V+ AND VL BYPASS CAPACITORS.
Figure 9. Buck-Boost Application
22
______________________________________________________________________________________
2.2MHz, Dual-Output Buck or Boost Converter with POR and Power-Fail Output
The transconductance error-amplifier gain is: GE / A = gm x RF The total loop gain at fC should be equal to 1 GM x GE / A = 1 or VOSC (ESR + 2 x fC x L OUT ) VOUT RF = 0.8 x VIN x gm x ESR Place a zero at or below the LC double pole: CF = 1 2 x RF x fLC Place a pole Calculate CI for a target unity crossover frequency, fC: CI = 2 x fC x LOUT x COUT x VOSC VIN x RF (fP1 = 1 2 x RI x CI at fZERO,ESR. 1 2 x fZERO, ESR x CI
MAX5072
RI =
Place a second zero, fZ2, at 0.2fC or at fLC, whichever is lower. R1 = 1 - RI 2 x fZ2 x CI (fP2 = 1 2 x RF x CCF ) at 1/2 the
Place a high-frequency pole at fP = 0.5 x fSW. Procedure 2 (See Figure 8): If the output capacitor used is a low-ESR ceramic type, the ESR frequency is usually far away from the targeted unity crossover frequency (fC). In this case, Type III compensation is recommended. Type III compensation provides two-pole zero pairs. The locations of the zero and poles should be such that the phase margin peaks at fC. fC f = P =5 fC The fZ is a good number to get about 60 phase margin at fC. However, it is important to place the two zeros at or below the double pole to avoid the conditional stability issue. Select a crossover frequency: f fC SW 20 Calculate the LC double-pole frequency, fLC: fLC = Place a zero fZ = where: 1 CF = 2 x 0.75 x fLC x RF and RF 10k. 1 at 0.75 x fLC 2 x R F x C F where: 1 2 x LOUT x COUT Place a second pole switching frequency. CCF =
CF (2 x 0.5 x fSW x RF x CF ) - 1
Boost Converter Compensation The boost converter compensation gets complicated due to the presence of a right-half-plane zero FZERO,RHP. The right-half-plane zero causes a drop inphase while adding positive (+1) slope to the gain curve. It is important to drop the gain significantly below unity before the RHP frequency. Use the following procedure to calculate the compensation components. Calculate the LC double-pole frequency, fLC, and the right half plane zero frequency. fLC = 1- D 2 x LOUTCOUT
(1 - D)2 R(MIN) fZERO, RHP = 2 x LOUT
D =1-
VIN
VOUT VOUT R(MIN) = IOUT(MAX)
Target the unity-gain crossover frequency for:
______________________________________________________________________________________ 23
2.2MHz, Dual-Output Buck or Boost Converter with POR and Power-Fail Output MAX5072
fC (fZ1 = fZERO, RHP 5
1
Improving Noise Immunity
In applications where the MAX5072 are subject to noisy environments, adjust the controller's compensation to improve the system's noise immunity. In particular, high-frequency noise coupled into the feedback loop causes jittery duty cycles. One solution is to lower the crossover frequency (see the Compensation section).
Place a zero
2 x R F x C F
) at 0.75 x fLC.
CF =
1 2 x 0.75 x fLC x RF
PC Board Layout Guidelines
Careful PC board layout is critical to achieve low switching losses and clean, stable operation. This is especially true for dual converters where one channel can affect the other. Refer to the MAX5072 EV kit data sheet for a specific layout example. Use a multilayer board whenever possible for better noise immunity. Follow these guidelines for good PC board layout: 1) For SGND, use a large copper plane under the IC and solder it to the exposed paddle. To effectively use this copper area as a heat exchanger between the PC board and ambient, expose this copper area on the top and bottom side of the PC board. Do not make a direct connection from the exposed pad copper plane to SGND (pin 29) underneath the IC. 2) Isolate the power components and high-current path from the sensitive analog circuitry. Use a separate PGND plane under the OUT1 and OUT2 sides (referred to as PGND1 and PGND2). Connect the PGND1 and PGND2 planes together at one point near the IC. 3) Keep the high-current paths short, especially at the ground terminals. This practice is essential for stable, jitter-free operation. 4) Connect SGND and PGND together close to the IC at the ground terminals of VL and V+ bypass capacitors. Do not connect them together anywhere else. 5) Keep the power traces and load connections short. This practice is essential for high efficiency. Use thick copper PC boards (2oz vs. 1oz) to enhance full-load efficiency. 6) Ensure that the feedback connection to COUT is short and direct. 7) Route high-speed switching nodes (BST_/VDD_, SOURCE_) away from the sensitive analog areas (BYPASS, COMP_, and FB_). Use the internal PC board layer for SGND as EMI shields to keep radiated noise away from the IC, feedback dividers, and analog bypass capacitors.
where RF 10k. Calculate CI for a target crossover frequency, fC: 2 VOSC (1 - D)2 + C x LO x CO CI = C x RF x VIN where C = 2fC. Place a pole (fP1 = 1 ) 2 x RI x CI at fZERO,RHP.
RI =
1 2 x fZERO,RHP x CI (fZ2 = 1 ) 2 x R1 x CI - RI
Place the second zero R1 = 1
at fLC.
2 x fLC x CI
Place the second pole the switching frequency. CCF =
(fP2 =
1 ) 2 x RF x CCF at 1/2
CF (2 x 0.5 fSW x RF x CF ) - 1
24
______________________________________________________________________________________
2.2MHz, Dual-Output Buck or Boost Converter with POR and Power-Fail Output
Layout Procedure
1) Place the power components first, with ground terminals adjacent (inductor, CIN_, and COUT_). Make all these connections on the top layer with wide, copper-filled areas (2oz copper recommended). 2) Group the gate-drive components (bootstrap diodes and capacitors, and VL bypass capacitor) together near the controller IC. 3) Make the DC-DC controller ground connections as follows: a) Create a small-signal ground plane underneath the IC. b) Connect this plane to SGND and use this plane for the ground connection for the reference (BYPASS), enable, compensation components, feedback dividers, and OSC resistor. c) Connect SGND and PGND together near the input bypass capacitors and the IC (this is the only connection between SGND and PGND).
MAX5072
Ordering Information (continued)
PART MAX5072ETJ+ MAX5072ATJ TEMP RANGE -40C to +85C -40C to +125C PIN-PACKAGE PKG CODE
Chip Information
TRANSISTOR COUNT: 5994 PROCESS: BiCMOS
32 Thin QFN-EP* T3255-4 (5mm x 5mm) 32 Thin QFN-EP* T3255-4 (5mm x 5mm) 32 Thin QFN-EP* T3255-4 (5mm x 5mm)
MAX5072ATJ+ -40C to +125C
*EP = Exposed pad. +Denotes lead-free package.
______________________________________________________________________________________
25
2.2MHz, Dual-Output Buck or Boost Converter with POR and Power-Fail Output MAX5072
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.)
26
______________________________________________________________________________________
QFN THIN.EPS
2.2MHz, Dual-Output Buck or Boost Converter with POR and Power-Fail Output
Package Information (continued)
(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.)
MAX5072
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 ____________________ 27 (c) 2006 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.

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