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MAX8532
(Rev.:2003)

Low-Noise, Low-Dropout, 200mA Linear Regulator in UCSP

Maxim Integrated 

Low-Noise, Low-Dropout,

200mA Linear Regulator in UCSP

Functional Diagram

IN

SHDN

SHUTDOWN

AND

POWER-ON

CONTROL

ERROR

AMP

MOS

DRIVER

WITH ILIMIT

OUT

THERMAL

SENSOR

1.25V

REF

MAX8532

GND

BP

Detailed Description

The MAX8532 is a low-power, low-dropout, low-quies-

cent current linear regulator designed primarily for bat-

tery-powered applications. For preset output voltages,

see the Output Voltage Selector Guide. The device

supplies up to 200mA for OUT. The MAX8532 consists

of a 1.25V reference, error amplifier, P-channel pass

transistor, reference bypass block, and internal feed-

back voltage divider.

The 1.25V bandgap reference is connected to the error

amplifier’s inverting input. The error amplifier compares

this reference with the feedback voltage and amplifies

the difference. If the feedback voltage is lower than the

reference voltage, the pass-transistor gate is pulled

lower, allowing more current to pass to the output and

increasing the output voltage. If the feedback voltage is

high, the pass-transistor gate is pulled up, allowing less

current to pass to the output. The output voltage is fed

back through an internal resistor voltage-divider con-

nected to the OUT pin.

Shutdown

The MAX8532 has a single shutdown control input

(SHDN). Drive SHDN low to shut down the output,

reducing supply current to 10nA. Connect SHDN to a

logic-high, or IN, for normal operation.

Internal P-Channel Pass Transistor

The MAX8532 features a 1Ω P-channel MOSFET pass

transistor. A P-channel MOSFET provides several advan-

tages over similar designs using PNP pass transistors,

including longer battery life. It requires no base drive,

reducing quiescent current. PNP-based regulators waste

considerable current in dropout when the pass transistor

saturates and also use high base-drive currents under

heavy loads. The MAX8532 does not suffer these prob-

lems and consumes only 90µA quiecent current whether

in dropout, light-load, or heavy-load applications (see the

Typical Operating Characteristics). Whereas a PNP-

based regulator has dropout voltage independent of the

load, a P-channel MOSFET’s dropout voltage is propor-

tional to load current, providing for low dropout voltage

at heavy loads and extremely low dropout voltage at

lighter loads.

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