3.3V/5V/Adjustable-Output,

Step-Up DC-DC Converters

4

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______________________________________________________________Pin Description

NAME

FUNCTION

1

SHDN

2

3/5

Selects the main output voltage setting; 5V when low, 3.3V when high.

–

FB

3

REF

4

LBO

5

LBI

6

OUT

7

GND

Power Ground. Must be low impedance; solder directly to ground plane.

8

LX

1A, 0.5

Ω N-Channel Power MOSFET Drain

1

–

2

3

4

5

6

7

8

PIN

MAX756

MAX757

Shutdown Input disables SMPS when low, but the voltage reference and low-battery com-

parator remain active.

Feedback Input for adjustable output operation. Connect to an external voltage divider

between OUT and GND.

1.25V Reference Voltage Output. Bypass with 0.22µF to GND (0.1µF if there is no external

reference load). Maximum load capability is 250µA source, 20µA sink.

Low-Battery Output. An open-drain N-channel MOSFET sinks current when the voltage at

LBI drops below +1.25V.

Low-Battery Input. When the voltage on LBI drops below +1.25V, LBO sinks current.

Connect OUT to the regulator output. It provides bootstrapped power to both devices,

and also senses the output voltage for the MAX756.

OUTPUT

VOLTAGE

50mV/div

HORIZONTAL = 50

µs/div

5V Mode

LOAD-TRANSIENT RESPONSE

OUTPUT

CURRENT

0mA to 200mA

_____________________________Typical Operating Characteristics (continued)

2V/div

HORIZONTAL = 5ms/div

5V Mode

START-UP DELAY

2V/div

3V

0V

5V

0V