Output Voltage Selection

The MAX8869 features Dual Mode operation. Connect

SET to GND (Figure 2) for preset voltage mode (see

Ordering Information). In adjustable mode, set the out-

put between +0.8V to +5.0V through two external resis-

tors connected as a voltage-divider to SET (Figure 3).

The output voltage is set by the following equation:

Since the input bias current at SET is nominally 50nA,

large resistance values can be used for R1 and R2 to

minimize power consumption without losing efficiency.

Up to 80kΩ is acceptable for R2.

In preset voltage mode, the impedance between SET

and ground should be less than 10kΩ. Otherwise, spu-

rious conditions could cause the voltage at SET to

exceed the 80mV Dual Mode threshold.

Shutdown

A logic low on SHDN disables the MAX8869. In shut-

down, the pass transistor, control circuitry, reference,

and all biases are turned off, reducing supply current to

typically 0.1µA. Connect SHDN to IN for normal opera-

tion. In shutdown, RST is low and the soft-start capaci-

tor is discharged.

RST Comparator

asserts when the output voltage falls out of regulation.

The open-drain RST goes low when OUT falls 8%

1A, Microcap, Low-Dropout,

Linear Regulator

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7

Figure 1. Functional Diagram

Figure 2. Typical Operating Circuit with Preset Output Voltage

MOSFET DRIVER

WITH FOLDBACK

CURRENT LIMIT

SHUTDOWN

LOGIC

0.8V

REFERENCE

SS

GND

SHDN

IN

OUT

RST

SET

6

μA

736mV

THERMAL

SENSOR

OUT

DELAY TIMER

IN

3ms

SHUTDOWN

ERROR AMP

DUAL MODE

COMPARATOR

80mV

DETECTOR

PMOS

NMOS

R1

R2

MAX8869

IN

IN

IN

IN

SHDN

SS

OUT

OUT

OUT

OUT

RST

SET

GND

ON

OFF

1

µF

1

µF

RESET

OUTPUT

MAX8869