Datasheet

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General Description

The MAX1951A high-efficiency, DC-DC step-down

switching regulator delivers up to 2A of output current.

The device operates from an input voltage range of 2.6V

to 5.5V and provides an adjustable output voltage from

0.8V to V

, making the MAX1951A ideal for on-board

postregulation applications. The MAX1951A total output

error is less than ±1.5% over load, line, and temperature.

The MAX1951A operates at a fixed frequency of 1MHz

with an efficiency of up to 94%. The high operating fre-

quency minimizes the size of external components.

Internal soft-start control circuitry reduces inrush current.

Short-circuit and thermal-overload protection improve

design reliability.

The MAX1951A can start up safely with a prebiased or

without a preexisting output. This feature simplifies track-

ing supply designs for core and I/O applications and

redundant supply designs.

The MAX1951A is available in an 8-pin SO package

and operates over the -40°C to +85°C extended tem-

perature range.

Applications

ASIC/DSP/µP/FPGA Core and I/O Voltages

Set-Top Boxes

Networking and Telecommunications

Servers

TVs

Features

o Compact 0.385in

Circuit Footprint

o 10µF Ceramic Input and Output Capacitors, 2µH

Inductor for 2A Output

o Efficiency Up to 94%

o 1.5% Output Accuracy Over Load, Line, and

Temperature

o Guaranteed 2A Output Current

o Operates from 2.6V to 5.5V Supply

o Adjustable Output from 0.8V to V

o Internal Digital Soft-Soft

o Short-Circuit and Thermal-Overload Protection

o 1MHz Switching Frequency Reduces Component

Size

o Enable Input Audio Shutdown for Reducing

Power Consumption

o Safe Startup into Prebiased Output

MAX1951A

1MHz, 2A, 2.6V to 5.5V Input, PWM DC-DC

Step-Down Regulator with Enable

________________________________________________________________

Maxim Integrated Products

Ordering Information

19-4689; Rev 0; 7/09

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.

EVALUATION KIT

AVAILABLE

PART TEMP RANGE PIN-PACKAGE

MAX1951AESA+ -40°C to +85°C 8 SO

MAX1951A

IN LX

COMP

OUTPUT

0.8V TO V

, UP TO 2A

INPUT

2.6V TO 5.5V

OFF

PGND GND

Typical Operating Circuit

Pin Configuration

PGND

COMPFB

LXEN

GND

TOP VIEW

MAX1951A

Denotes a lead(Pb)-free/RoHS-compliant package.

Summary of content (12 pages)

PAGE 1
9-4689; Rev 0; 7/09 KIT ATION EVALU E L B A IL AVA 1MHz, 2A, 2.6V to 5.5V Input, PWM DC-DC Step-Down Regulator with Enable Features The MAX1951A high-efficiency, DC-DC step-down switching regulator delivers up to 2A of output current. The device operates from an input voltage range of 2.6V to 5.5V and provides an adjustable output voltage from 0.8V to VIN, making the MAX1951A ideal for on-board postregulation applications. The MAX1951A total output error is less than ±1.
PAGE 2
MAX1951A 1MHz, 2A, 2.6V to 5.5V Input, PWM DC-DC Step-Down Regulator with Enable ABSOLUTE MAXIMUM RATINGS IN, VCC to GND ........................................................-0.3V to +6V COMP, FB, EN to GND...............................-0.3V to (VCC + 0.3V) LX Current (Note 1).............................................................±4.5A PGND to GND..............................................Internally connected Continuous Power Dissipation (TA = +70°C) 8-Pin SO (derate 12.2mW/°C above +70°C)....
PAGE 3
1MHz, 2A, 2.6V to 5.5V Input, PWM DC-DC Step-Down Regulator with Enable (VIN = VCC = VEN = 3.3V, VPGND = VGND = 0V, FB in regulation, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 3) PARAMETER CONDITIONS MIN TYP MAX UNITS 0.16 0.24 0.35 Ω 2.2 3.1 4.5 LX Current-Sense Transimpedance From LX to COMP, VIN = 2.6V to 5.5V LX Current-Limit Threshold Duty = 100%, VIN = 2.6V to 5.5V LX Leakage Current VIN = 5.5V LX Switching Frequency VIN = 2.6V to 5.
PAGE 4
Typical Operating Characteristics (continued) (Typical values are at VIN = VCC = 5V, VOUT = 1.5V, IOUT = 1.5A, and TA = +25°C, unless otherwise noted. See Figure 2.) LOAD TRANSIENT (90% TRANSIENT) LOAD TRANSIENT (50% TRANSIENT) LOAD REGULATION 0.40 0.30 MAX1951A toc06 MAX1951A toc05 MAX1951A toc04 0.50 OUTPUT VOLTAGE DEVIATION (%) MAX1951A 1MHz, 2A, 2.6V to 5.
PAGE 5
1MHz, 2A, 2.6V to 5.5V Input, PWM DC-DC Step-Down Regulator with Enable SHUTDOWN WAVEFORMS (VIN = 3.3V, VOUT = 2.5V, RL = 1.5I) MAX1951A toc11 SUPPLY CURRENT vs. INPUT VOLTAGE MAX1951A toc12 8 7 EN 5V/div SUPPLY CURRENT (mA) EN 2V/div LX 5V/div VOUT = 3.3V VOUT = 2.5V MAX1951A toc13 STARTUP INTO PREBIASED OUTPUT LX 2V/div VOUT 2V/div 6 5 4 3 2 VOUT 2V/div 1 0 1ms/div 2.5 20Fs/div 3.0 3.5 4.0 4.5 5.0 5.5 INPUT VOLTAGE (V) FEEDBACK VOLTAGE vs. TEMPERATURE CASE TEMPERATURE vs.
PAGE 6
MAX1951A 1MHz, 2A, 2.6V to 5.5V Input, PWM DC-DC Step-Down Regulator with Enable Pin Description PIN NAME FUNCTION 1 VCC Supply Voltage. Bypass with a 0.1µF capacitor to ground and a 10Ω resistor to IN. 2 EN Enable Input. Connect to VCC for normal operation. Connect to GND to disable the MAX1951A. 3 GND 4 FB Feedback Input. Connect an external resistordivider from the output to FB and GND to set the output to a voltage between 0.8V and VIN. 5 COMP Regulator Compensation.
PAGE 7
1MHz, 2A, 2.6V to 5.5V Input, PWM DC-DC Step-Down Regulator with Enable MAX1951A POSITIVE AND NEGATIVE CURRENT LIMITS VCC IN OSC CLOCK CURRENT SENSE PWM CONTROL RAMP GEN SLOPE COMP LX PREBIAS CLAMP ERROR SIGNAL THERMAL SHUTDOWN PGND ZEROCROSSING DETECTOR FB gm COMP SOFT-START/ UVLO EN DAC BANDGAP REF 1.25V MAX1951A GND Figure 1. Functional Diagram VCC Decoupling Due to the high switching frequency and tight output tolerance (1.5%), decouple VCC with a 0.
PAGE 8
MAX1951A 1MHz, 2A, 2.6V to 5.5V Input, PWM DC-DC Step-Down Regulator with Enable Design Procedure Adjustable Output Voltage The MAX1951A provides an adjustable output voltage between 0.8V and VIN. Connect FB to output for 0.8V output. To set the output voltage of the MAX1951A to a voltage greater than VFB (0.8V typ), connect the output to FB and GND using a resistive divider, as shown in Figure 2.
PAGE 9
1MHz, 2A, 2.6V to 5.5V Input, PWM DC-DC Step-Down Regulator with Enable Compensation Design The double pole formed by the inductor and output capacitor of most voltage-mode controllers introduces a large phase shift that requires an elaborate compensation network to stabilize the control loop.
PAGE 10
MAX1951A 1MHz, 2A, 2.6V to 5.5V Input, PWM DC-DC Step-Down Regulator with Enable RLOAD = VOUT/IOUT(MAX) = 1.5V/2A = 0.75Ω fpMOD = [1/(2π x COUT x (RLOAD + RESR)] = [1/(2 x π x10 x10-6 x (0.75 + 0.01)] = 20.9Hz. fzESR = [1/(2π x COUT x RESR)] = [1/(2 x π x 10 x10-6 x 0.01)] = 1.59MHz. For a 2µH output inductor, pick the closed-loop unitygain crossover frequency (fC) at 200kHz. Determine the power modulator gain at fC: GMOD(fc) = gmc x RLOAD x fpMOD/fC = 4.2 x 0.75 x 20.9kHz/200kHz = 0.
PAGE 11
1MHz, 2A, 2.6V to 5.5V Input, PWM DC-DC Step-Down Regulator with Enable IN C4 0.1µF MAX1951A L1 2µH 2.6V TO 5.5V 1.5V AT 2A LX R4 10Ω MAX1951A FB VCC R1 51.1kΩ EN ON R3 13.0kΩ 1% OFF COMP C1 10µF GND C2 220pF PGND R2 15.0kΩ 1% C3 10µF OUTPUT COMPONENT VALUES VOLTAGE (V) R1 (kΩ) R2 (kΩ) R3 (kΩ) C2 (pF) 470 SHORT OPEN 0.8 10 150 13 15 1.5 52.3 150 31.6 15 2.5 86.6 150 46.4 15 3.3 115 Figure 2.
PAGE 12
MAX1951A 1MHz, 2A, 2.6V to 5.5V Input, PWM DC-DC Step-Down Regulator with Enable Table 2. External Components List COMPONENT (FIGURE 2) FUNCTION DESCRIPTION L1 Output inductor C1 Input filtering capacitor 10µF ±20%, 6.3V X5R capacitor Taiyo Yuden JMK316BJ106ML or TDK C3216X5R0J106MT C2 Compensation capacitor 220pF ±10%, 50V capacitor Murata GRM1885C1HZZ1JA01 or Taiyo Yuden UMK107CH221KZ C3 Output filtering capacitor 10µF ±20%, 6.