_______________General Description

The MAX1649/MAX1651 BiCMOS, step-down, DC-DC

switching controllers provide high efficiency over loads

ranging from 1mA to more than 2.5A. A unique, current-

limited pulse-frequency-modulated (PFM) control scheme

gives these devices the benefits of pulse-width-modula-

tion (PWM) converters (high efficiency at heavy loads),

while using only 100µA of supply current (vs. 2mA to

10mA for PWM converters). Dropout performance down

to 300mV is provided by a high switch duty cycle (96.5%)

and a low current-sense threshold (110mV).

A high switching frequency (up to 300kHz) allows these

devices to use miniature external components.

The MAX1649/MAX1651 have dropout voltages less

than 0.3V at 500mA and accept input voltages up to

16V. Output voltages are preset at 5V (MAX1649), or

3.3V (MAX1651). They can also be adjusted to any

voltage from 1.5V to the input voltage by using two

resistors.

These step-down controllers drive external P-channel

MOSFETs at loads greater than 12.5W. If less power is

required, use the MAX639/MAX640/MAX653 step-down

converters with on-chip FETs, which allow up to a

225mA load current.

________________________Applications

PDAs

High-Efficiency Step-Down Regulation

5V-to-3.3V Green PC Applications

Battery-Powered Applications

____________________________Features

o More than 90% Efficiency (10mA to 1.5A Loads)

o More than 12.5W Output Power

o Less than 0.3V Dropout Voltage at 500mA

o 100µA Max Quiescent Supply Current

o 5µA Max Shutdown Supply Current

o 16V Max Input Voltage

o 5V (MAX1649), 3.3V (MAX1651), or Adjustable

Output Voltage

o Current-Limited Control Scheme

o Up to 300kHz Switching Frequency

o Up to 96.5% Duty Cycle

______________Ordering Information

5V/3.3V or Adjustable, High-Efficiency,

Low-Dropout, Step-Down DC-DC Controllers

________________________________________________________________

Maxim Integrated Products

1

1

2

3

4

8

7

6

5

GND

EXT

CS

V+

REF

SHDN

FB

OUT

DIP/SO

TOP VIEW

MAX1649

MAX1651

__________________Pin Configuration

__________Typical Operating Circuit

Call toll free 1-800-998-8800 for free samples or literature.

19-0305; Rev 2; 9/95

PART

TEMP. RANGE

PIN-PACKAGE

MAX1649CPA

0°C to +70°C

8 Plastic DIP

MAX1649CSA

0°C to +70°C

8 SO

MAX1649C/D

0°C to +70°C

Dice*

MAX1649EPA

-40°C to +85°C

8 Plastic DIP

MAX1649ESA

-40°C to +85°C

8 SO

MAX1651

V+

CS

SHDN

FB

GND

ON/OFF

P

EXT

REF

OUT

OUTPUT

3.3V

INPUT

3.6V TO 16V

MAX1651CPA

0°C to +70°C

8 Plastic DIP

MAX1651CSA

0°C to +70°C

8 SO

MAX1651C/D

0°C to +70°C

Dice*

MAX1651EPA

-40°C to +85°C

8 Plastic DIP

MAX1651ESA

-40°C to +85°C

8 SO