350mA, 16.5V Input,

Low-Dropout Linear Regulators

6

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MAX1658

MAX1659

P

P

OUT

SET

IN

SHDN

MOSFET

DRIVER

WITH

CURRENT

LIMIT

R2

R1

65mV

GND

DUAL-MODE

COMPARATOR

1.21V

REFERENCE

THERMAL

SENSOR

ERROR

AMPLIFIER

Figure 1. Functional Diagram

_______________Detailed Description

The MAX1658/MAX1659 are micropower, low-dropout

linear regulators featuring Dual Mode™ operation,

which allows them to deliver an adjustable (1.25V to

16.5V) or preset (3.3V for the MAX1658, 5V for

MAX1659) output. They supply up to 350mA while

requiring only 120µA of supply current (typically 30µA

with no load). The devices include thermal shutdown

circuitry, output current limiting, a P-channel pass tran-

sistor, a Dual Mode comparator, and a feedback volt-

age divider. Figure 1 shows the functional diagram.

The 1.21V reference is connected to the amplifier’s

inverting input. The error amplifier compares this refer-

ence with the selected feedback voltage and amplifies

the difference. The error signal applies the drive to the

P-channel pass transistor. If the feedback voltage is

lower than the reference voltage, the transistor’s gate is

pulled lower, increasing output current.

The output voltage is fed back through an internal

resistor network or an external user-selected network.

The Dual Mode comparator examines the voltage at the

SET pin and selects either the internal or external feed-

back path. If SET is below 65mV, internal feedback sets

the MAX1658’s output voltage to 3.3V and the

MAX1659’s to 5V. Otherwise, external feedback is used

for an adjustable output between 1.25V and 16.5V.

Additional features include internal current limiting,

reverse battery protection, thermal-overload protection,

and a 1µA shutdown mode.