Detailed Description

The MAX1589 is a low-dropout, low-quiescent-current,

high-accuracy linear regulator designed primarily for

battery-powered applications. The device supplies

loads up to 500mA and is available with preset output

voltages from +0.75V to +3.0V. As illustrated in Figure 1,

the MAX1589 contains a reference, an error amplifier, a

P-channel pass transistor, an internal feedback voltage-

divider, and a power-good comparator.

The error amplifier compares the 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 too high, the pass-

transistor gate is pulled up, allowing less current to

pass to the output.

Internal P-Channel Pass Transistor

The MAX1589 features a 0.33

MOSFET pass transistor. Unlike similar designs using

PNP pass transistors, P-channel MOSFETs require no

base drive, which reduces quiescent current. PNP-

based regulators also waste considerable current in

dropout when the pass transistor saturates and use

high base-drive currents under large loads. The

MAX1589 does not suffer from these problems and

consumes only 90µA (typ) of quiescent current under

heavy loads, as well as in dropout.

Shutdown

Pull SHDN low to enter shutdown. During shutdown, the

output is disconnected from the input, an internal 1.5k

Ω

resistor pulls OUT to GND, RESET is actively pulled

low, and supply current drops below 1µA.

R

RE

ES

SE

ET

T Output

The MAX1589’s microprocessor (µP) supervisory cir-

cuitry asserts a guaranteed logic-low reset during

power-up, power-down, and brownout conditions down

Current Limit

The MAX1589 monitors and controls the pass transis-

tor’s gate voltage, limiting the output current to 850mA

output voltage drops.

Thermal-Overload Protection

Thermal-overload protection limits total power dissipa-

tion in the MAX1589. When the junction temperature

exceeds +165°C, a thermal sensor turns off the pass

Low-Input-Voltage, 500mA LDO Regulator

with

R

RE

ES

SE

ET

6

_______________________________________________________________________________________

PART

SOT23

TDFN

NAME

FUNCTION

16

IN

Regulator Input. Supply voltage can range from +1.62V to +3.6V. Bypass IN with at least a

1µF ceramic capacitor to GND (see the Capacitor Selection and Regulator Stability

section).

2

—

GND

Ground. GND also functions as a heatsink. Solder GND to a large pad or circuit-board

ground plane to maximize SOT23 power dissipation.

—

4

GND

Ground

35

SHDN

Active-Low Shutdown Input. A logic low reduces supply current to below 1µA. Connect to

IN or logic high for normal operation.

43

RESET

Active-Low, Open-Drain Reset Output.

RESET rises 100ms after the output has achieved

regulation.

the MAX1589 is shut down.

5

2

I.C.

Internally Connected. Leave floating or connect to GND.

6

1

OUT

Regulator Output. Sources up to 500mA. Bypass with a 4.7µF low-ESR ceramic capacitor

to GND.

—

Exposed

Pad

EP

Ground. EP also functions as a heatsink. Solder EP to a large pad or circuit-board ground

plane to maximize TDFN power dissipation.

Pin Description