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MAX1735
(Rev.:2000)

200mA, Negative-Output, Low-Dropout Linear Regulator in SOT23

Maxim Integrated 

200mA, Negative-Output, Low-Dropout

Linear Regulator in SOT23

CIN

ON

GND

OFF

ON

IN

SHUTDOWN

LOGIC

SHDN

THERMAL

SENSOR

ERROR

AMPLIFIER

MAX1735

VREF

-1.25V

Dual Mode

COMPARATOR

-270mV

NMOS

PASS

TRANSISTOR

OUT

COUT

R1

SET

R2

GND

Figure 1. Functional Diagram

Detailed Description

The MAX1735 is a low-dropout negative linear voltage

regulator. It features Dual Mode operation, allowing a

fixed -5.0V, -3.0V, or -2.5V output voltage or an

adjustable output from -1.25V to -5.5V. The regulator is

guaranteed to supply 200mA of output current. It fea-

tures 60dB power-supply rejection for noise-sensitive

applications and a low 85µA operating current that opti-

mizes it for battery-operated devices.

As Figure 1 illustrates, the device consists of an internal

-1.25V reference, an error amplifier, an N-channel

MOSFET, an internal precision-trimmed feedback volt-

age-divider, and a Dual Mode comparator.

The -1.25V reference is connected to the inverting input

of the error amplifier. The error amplifier compares the

reference voltage with the selected feedback voltage

and amplifies the difference. The error amplifier drives

the MOSFET to control the output voltage.

The feedback voltage for regulation is generated by

either an internal or external resistive voltage-divider

connected from OUT to SET. The internal Dual Mode

comparator selects the feedback path based on VSET.

Connect SET to GND to use the internal feedback path,

setting the output voltage to the preset value. If an

external voltage-divider is used, see Output Voltage

Selection.

Internal N-Channel MOSFET

The MAX1735 features an N-channel MOSFET pass

transistor. Unlike similar designs using NPN bipolar

pass transistors, N-channel MOSFETs require extreme-

ly low drive currents, reducing overall quiescent cur-

rent. Also, NPN-based regulators consume still more

base current in dropout conditions when the pass tran-

sistor saturates. The MAX1735 does not suffer from

these problems, consuming only 125µA total current at

full load and in dropout.

Output Voltage Selection

The MAX1735 features Dual Mode operation, allowing for

a preset or adjustable output voltage. In preset voltage

mode, the output of the MAX1735 is set to -5.0V, -3.0V, or

-2.5V (see Ordering Information). Select this mode by

connecting SET to GND (Figure 2).

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