Datasheet

ManualsBrandsMAXIM INTEGRATED ManualsPMICsPMIC - DC/DC voltage regulator Holder QSOP 16

General Description

The MAX1970/MAX1971/MAX1972 dual-output current-

mode PWM buck regulators operate from 2.6V to 5.5V

input and deliver a minimum of 750mA on each output.

The MAX1970 and MAX1972 operate at a fixed 1.4MHz

(MAX1971 operates at 700kHz) to reduce output induc-

tor and capacitor size and cost. Switching the regula-

tors 180° out-of-phase also reduces the input capacitor

size and cost. Ceramic capacitors can be used for

input and output.

The output voltages are programmable from 1.2V to V

using external feedback resistors, or can be preset to

1.8V or 3.3V for output 1 and 1.5V or 2.5V for output 2.

When one output is higher than 1.2V, the second can

be configured down to sub-1V levels. Output accuracy

is better than ±1% over variations in load, line, and tem-

perature. Internal soft-start reduces inrush current dur-

ing startup.

All devices feature power-on reset (POR). The

MAX1971 includes a reset input (RSI), which forces

POR low for 175ms after RSI goes low. The MAX1970

and MAX1972 include an open-drain power-fail output

(PFO) that monitors input voltage and goes high when

the input falls below 3.94V. For USB-powered xDSL

modems, this output can be used to detect USB power

failure. A minimum switching frequency of 1.2MHz

ensures operation outside the xDSL band.

Applications

Features

o Current-Mode, 1.4MHz Fixed-Frequency PWM

Operation

o 180° Out-of-Phase Operation Reduces Input

Capacitor

o ±1% Output Accuracy Over Load, Line, and

Temperature Ranges

o 750mA Guaranteed Output Current

o 2.6V to 5.5V Input

o Power-On Reset Delay of 16.6ms (MAX1970) or

175ms (MAX1971 and MAX1972)

o Power-Fail Output (MAX1970 and MAX1972 Only)

o Power-On Reset Input (MAX1971 Only)

o Operation Outside xDSL Band

o Ultra-Compact Design with Smallest External

Components

o Outputs Adjustable from 0.8V to V

or 1.8V/3.3V

and 1.5V/2.5V Preset

o All-Ceramic Capacitor Application

o Soft-Start Reduces Inrush Current

MAX1970/MAX1971/MAX1972

Dual, 180° Out-of-Phase, 1.4MHz, 750mA Step-

Down Regulator with POR and RSI/PFO

________________________________________________________________

Maxim Integrated Products

LX1 PGND

LX2

FBSEL1

FBSEL2

PF0 (MAX1970/MAX1972)

RSI (MAX1971)

POR

TOP VIEW

MAX1970

MAX1971

MAX1972

QSOP

COMP1

COMP2

FB1

FB2

REF

GND

Pin Configuration

RSI

COMP1

COMP2

FBSEL1

FBSEL2

REF

POR

OUT1

1.8V

750mA

OUT2

2.5V

750mA

RSI

LX1

FB2

FB1

LX2

PGND

MAX1971

2.6V TO 5.5V

Typical Operating Circuit

19-2297; Rev 1; 2/09

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,

or visit Maxim’s website at www.maxim-ic.com.

xDSL Modems

xDSL Routers

Copper Gigabit SFP

and GBIC Modules

USB-Powered Devices

Dual LDO Replacement

Ordering Information

PART TEMP RANGE PIN-PACKAGE

MAX1970EEE -40°C to +85°C 16 QSOP

MAX1971EEE -40°C to +85°C 16 QSOP

MAX1972EEE -40°C to +85°C 16 QSOP

Summary of content (21 pages)

PAGE 1
9-2297; Rev 1; 2/09 Dual, 180° Out-of-Phase, 1.4MHz, 750mA StepDown Regulator with POR and RSI/PFO The MAX1970/MAX1971/MAX1972 dual-output currentmode PWM buck regulators operate from 2.6V to 5.5V input and deliver a minimum of 750mA on each output. The MAX1970 and MAX1972 operate at a fixed 1.4MHz (MAX1971 operates at 700kHz) to reduce output inductor and capacitor size and cost. Switching the regulators 180° out-of-phase also reduces the input capacitor size and cost.
PAGE 2
MAX1970/MAX1971/MAX1972 Dual, 180° Out-of-Phase, 1.4MHz, 750mA StepDown Regulator with POR and RSI/PFO ABSOLUTE MAXIMUM RATINGS IN, EN, FBSEL1, FBSEL2, PFO, POR, RSI, VCC to GND ...................................................-0.3V to +6V COMP1, COMP2, FB1, FB2, REF to GND .............................................-0.3V to (VCC + 0.3V) LX1, LX2 to PGND .......................................-0.3V to (VIN + 0.3V) PGND to GND .......................................................-0.3V to +0.
PAGE 3
Dual, 180° Out-of-Phase, 1.4MHz, 750mA StepDown Regulator with POR and RSI/PFO (VIN = VCC = VEN = 5V, R POR = 100kΩ to IN, RPFO = 100kΩ to IN, VRSI = 0, CREF = 0.1µF, FBSEL1 = unconnected, FBSEL2 = unconnected, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS MIN TYP MAX UNITS COMP1 AND COMP2 COMP1 Transconductance FB1 = COMP1, VCOMP1 = 1.2V FBSEL1 = unconnected 35 55 85 µS COMP2 Transconductance FB2 = COMP2, VCOMP2 = 1.
PAGE 4
MAX1970/MAX1971/MAX1972 Dual, 180° Out-of-Phase, 1.4MHz, 750mA StepDown Regulator with POR and RSI/PFO ELECTRICAL CHARACTERISTICS (continued) (VIN = VCC = VEN = 5V, R POR = 100kΩ to IN, RPFO = 100kΩ to IN, VRSI = 0, CREF = 0.1µF, FBSEL1 = unconnected, FBSEL2 = unconnected, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS MIN TYP MAX 4.04 4.
PAGE 5
Dual, 180° Out-of-Phase, 1.4MHz, 750mA StepDown Regulator with POR and RSI/PFO (VIN = VCC = VEN = 5V, VFB1 = VFB2 = 1.15V, R POR = 100kΩ to IN, RPFO = 100kΩ to IN, RSI = 0, CVCC = 0.1µF, CREF = 0.1µF, FBSEL1 = unconnected, FBSEL2 = unconnected, TA = -40°C to +85°C.) (Note 2) PARAMETER CONDITIONS MIN TYP MAX FBSEL1 = GND 30 120 30 120 FB1 Input Resistance Measured from FB1 to GND FBSEL1 = VCC FB2 Input Resistance Measured from FB2 to GND FBSEL2 = GND 22.5 90 FBSEL2 = VCC 22.
PAGE 6
MAX1970/MAX1971/MAX1972 Dual, 180° Out-of-Phase, 1.4MHz, 750mA StepDown Regulator with POR and RSI/PFO ELECTRICAL CHARACTERISTICS (continued) (VIN = VCC = VEN = 5V, VFB1 = VFB2 = 1.15V, R POR = 100kΩ to IN, RPFO = 100kΩ to IN, RSI = 0, CVCC = 0.1µF, CREF = 0.1µF, FBSEL1 = unconnected, FBSEL2 = unconnected, TA = -40°C to +85°C.
PAGE 7
Dual, 180° Out-of-Phase, 1.4MHz, 750mA StepDown Regulator with POR and RSI/PFO EFFICIENCY vs. LOAD CURRENT 80 60 VOUT1 = 1.8V 50 40 30 VOUT2 = 1.5V MAX1970/ MAX1972 VIN = 5.0V 10 60 VOUT2 = 1.5V 50 VOUT2 = 2.5V 40 70 0.1 40 10 0.1 1 0.01 0.1 1 LOAD CURRENT (A) LOAD CURRENT (A) EFFICIENCY vs. LOAD CURRENT INPUT CURRENT vs. OUTPUT CURRENT REFERENCE VOLTAGE vs. REFERENCE LOAD CURRENT 50 40 30 20 VOUT2 = 2.5V 300 250 200 VOUT1 = 1.8V 150 100 MAX1971 VIN = 3.3V 10 350 0.
PAGE 8
Typical Operating Characteristics (continued) (TA = +25°C, unless otherwise noted.) LOAD-TRANSIENT RESPONSE MAX1970TOC10 LOAD-TRANSIENT RESPONSE MAX1970TOC09 VOUT2 VOUT1 IOUT2 IOUT1 MAX1970/MAX1972 MAX1970/MAX1972 40µs/div 40µs/div VIN = 5V VOUT2 = 1.5V, 100mV/div IOUT2 = 300mA TO 600mA RC2 = 39kΩ, CC2 = 680pF VIN = 5V VOUT1 = 3.3V, 100mV/div IOUT1 = 300mA TO 600mA RC1 = 82kΩ, CC1 = 680pF MAXIMUM OUTPUT TRANSIENT DURATION vs.
PAGE 9
Dual, 180° Out-of-Phase, 1.4MHz, 750mA StepDown Regulator with POR and RSI/PFO PFO AND RISING INPUT VOLTAGE RSI AND POR TIMING MAX1970TOC14 MAX1970TOC13 VRSI VIN 4V PF0 0 2V/div 4V 2V/div VPOR 0 4ms/div 40ms/div VOUT1 = 1.8V, VOUT2 = 2.5V VIN = 5V VOUT1 = 1.8V, VOUT2 = 2.5V IOUT1 = 500mA, IOUT2 = 500mA MAX1970TOC15 VIN POR MAX1970TOC16 ENABLE RESPONSE PFO AND FALLING INPUT VOLTAGE 4V 0 2V/div 4V EN 5V/div VOUT1 PF0 VOUT2 0 4ms/div VOUT1 = 1.8V, VOUT2 = 2.
PAGE 10
Typical Operating Characteristics (continued) (TA = +25°C, unless otherwise noted.) SHUTDOWN RESPONSE POR MAX1970TOC17 MAX1970/MAX1971/MAX1972 Dual, 180° Out-of-Phase, 1.4MHz, 750mA StepDown Regulator with POR and RSI/PFO EN 5V/div VOUT1 VOUT2 5ms/div MAX1970 VIN = 5V VOUT1 = 3.3V, VOUT2 = 2.5V IOUT1 = 375mA, IOUT2 = 375mA Pin Description PIN FUNCTION MAX1971 1 LX1 LX1 Inductor Connection 1. Connect an inductor between LX1 and OUT1. 2 VCC VCC Analog Supply Voltage. Bypass with 0.
PAGE 11
Dual, 180° Out-of-Phase, 1.4MHz, 750mA StepDown Regulator with POR and RSI/PFO PIN NAME FUNCTION MAX1970/MAX1972 MAX1971 9 POR POR 10 EN EN Enable Input. Drive high to turn on both OUT1 and OUT2. Drive low to place the device in shutdown. PFO — Power-Fail Output. Open-drain output goes high when VCC drops below 3.94V. Useful for detecting a valid USB input voltage. — RSI Noninverting Reset Input. Causes POR to go low when RSI is high.
PAGE 12
MAX1970/MAX1971/MAX1972 Dual, 180° Out-of-Phase, 1.4MHz, 750mA StepDown Regulator with POR and RSI/PFO VCC REGULATOR 1 IN FB1 FB SELECT FBSEL1 ERROR SIGNAL SLOPE COMP PWM CONTROL LX1 CURRENT SENSE COMP1 CLAMP PGND SOFT-START REF ÷2(MAX1970/ MAX1972)/ ÷4(MAX1971) REFERENCE VOLTAGE 1.2V 2.8MHz OSCILLATOR MAX1971 ONLY RSI POR POR THERMAL SHUTDOWN MAX1970/MAX1972 ONLY EN VOK PFO PFO COMP2 REGULATOR 2 FB2 FBSEL2 MAX1970 MAX1971 MAX1972 GND Figure 1.
PAGE 13
Dual, 180° Out-of-Phase, 1.4MHz, 750mA StepDown Regulator with POR and RSI/PFO Current Limit The internal MOSFET has a current limit of 1.2A (typ). If the current flowing out of LX_ exceeds this maximum, the high-side MOSFET turns off and the synchronous rectifier MOSFET turns on. This lowers the duty cycle and causes the output voltage to droop until the current limit is no longer exceeded. There is also a synchronous rectifier current limit of -0.85A.
PAGE 14
MAX1970/MAX1971/MAX1972 Dual, 180° Out-of-Phase, 1.4MHz, 750mA StepDown Regulator with POR and RSI/PFO VOUT POR TD ~1V PKMAX TD TRESET = 1µs MIN RSI 4.04V 3.94V VIN PFO Figure 2. Timing Diagram Design Procedure Output Voltage Selection Both output voltages can be selected in three different ways as indicated by Table 1. Each output has two preset voltages that can be set using FBSEL_ and it can also be set to any voltage from 0.8V to VIN by using an external resistor voltage-divider.
PAGE 15
Dual, 180° Out-of-Phase, 1.4MHz, 750mA StepDown Regulator with POR and RSI/PFO VCC MAX1970/MAX1971/MAX1972 VIN 3.3V TO 5.5V 10Ω 10µF 0.1µF 100kΩ 100kΩ 2 14 11 PFO EN 10 680pF 82kΩ 680pF 39kΩ 3 6 12 PFO VCC IN EN POR LX1 MAX1972 COMP1 FB1 POR 9 1 4.7µH 4 10µF COMP2 LX2 FBSEL2 VCC FB2 VOUT1 3.3V 15 4.7µH VOUT2 1.5V 5 13 0.1µF FBSEL1 7 REF GND 8 10µF PGND 16 Figure 3. Typical Application Circuit 1 VIN 3.3V TO 5.5V VCC 10Ω 10µF 0.
PAGE 16
MAX1970/MAX1971/MAX1972 Dual, 180° Out-of-Phase, 1.4MHz, 750mA StepDown Regulator with POR and RSI/PFO VIN 2.6V TO 5.5V 10Ω 10µF 0.1µF 100kΩ 11 RSI 10 EN 680pF RC1 680pF RC2 3 14 IN 2 VCC RSI POR LX1 EN 13 7 1 MAX1971 R1b FBSEL1 FBSEL2 0.1µF 10µF 4 COMP2 REF VOUT1 R1a LX2 12 4.7µH COMP1 FB1 6 POR 9 FB2 4.7µH 15 5 VOUT2 R2a 10µF PGND 16 GND 8 R2b Figure 5. Setting the Output Voltage with External Resistors VIN 3V TO 3.6V 10Ω VCC 0.
PAGE 17
Dual, 180° Out-of-Phase, 1.4MHz, 750mA StepDown Regulator with POR and RSI/PFO FBSEL1 OUTPUT 1 FBSEL2 OUTPUT 2 VCC 3.3V VCC 2.5V GND 1.8V GND 1.5V Open Ext Divider Open Ext Divider For most designs, a reasonable inductor value (LINIT) is derived from the following equation: LINIT = VOUT ( VIN − VOUT ) The key selection parameters for the output capacitor are its capacitance, ESR, ESL, and the voltage rating requirements.
PAGE 18
MAX1970/MAX1971/MAX1972 Dual, 180° Out-of-Phase, 1.4MHz, 750mA StepDown Regulator with POR and RSI/PFO troller can respond, the output deviates further, depending on the inductor and output capacitor values. After a short time (see the Typical Operating Characteristics), the controller responds by regulating the output voltage back to its nominal state. The controller response time depends on the closed-loop bandwidth.
PAGE 19
Dual, 180° Out-of-Phase, 1.4MHz, 750mA StepDown Regulator with POR and RSI/PFO VOUT = 2.5V IOUT(MAX) = 0.6A COUT = 10µF RESR = 0.010Ω gmEA = 50µS gmC = 2S fSWITCH = 1.4MHz RLOAD = VOUT/IOUT(MAX) = 2.5V/0.6A = 4.167Ω fp MOD = 1/[2π C OUT (R LOAD + R ESR )] = 1/[2π x 10 x 10-6 (4.167 + 0.01)] = 3.80kHz. fzESR = 1/[2π COUT RESR] = 1/[2π x 10 x 10-6 x 0.01] = 1.59MHz. Pick a closed-loop unity-gain frequency (fc) of 50kHz. The power modulator gain at fc is: GMOD(fc) = gmc x RLOAD x fpMOD/fc = 2 x 4.167 x 3.
PAGE 20
MAX1970/MAX1971/MAX1972 Dual, 180° Out-of-Phase, 1.4MHz, 750mA StepDown Regulator with POR and RSI/PFO Package Information Chip Information TRANSISTOR COUNT: 5428 PROCESS: BiCMOS 20 For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
PAGE 21
Dual, 180° Out-of-Phase, 1.4MHz, 750mA StepDown Regulator with POR and RSI/PFO REVISION NUMBER REVISION DATE 0 1/02 Initial release — 1 2/09 Updated formula in the Output Voltage Selection section. 14 DESCRIPTION PAGES CHANGED 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.