_______________Detailed Description

The MAX8877/MAX8878 are low-noise, low-dropout,

low-quiescent-current linear regulators designed pri-

marily for battery-powered applications. The parts are

available with preset output voltages ranging from 1.5V

to 5V, in 100mV increments. These devices can supply

loads up to 150mA. As illustrated in Figure 1, the

MAX8877/MAX8878 consist of a 1.25V reference, error

amplifier, P-channel pass transistor, 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, which allows more current to pass to the output

and increases the output voltage. If the feedback volt-

age is too 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 connected to the OUT pin.

An external bypass capacitor connected to the BP pin

reduces noise at the output. Additional blocks include a

current limiter, reverse battery protection, thermal sen-

sor, and shutdown logic. The MAX8878 also includes

an auto-discharge function, which actively discharges

the output voltage to ground when the device is placed

in shutdown mode.

Low-Noise, Low-Dropout, 150mA Linear

Regulators with '2982 Pinout

6

_______________________________________________________________________________________

SHUTDOWN

AND

POWER-ON

CONTROL

ERROR

AMP

1.25V

REF

P

N

*

OUT

BP

* AUTO-DISCHARGE, MAX8878 ONLY

GND

IN

SHDN

MAX8877

MAX8878

MOS DRIVER

THERMAL

SENSOR

REVERSE

BATTERY

PROTECTION

Figure 1. Functional Diagram

______________________________________________________________Pin Description

PIN

NAME

FUNCTION

1IN

Regulator Input. Supply voltage can range from 2.5V to 6.5V. Bypass with a 1

µF capacitor to GND

(see Capacitor Selection and Regulator Stability section).

2

GND

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

plane to maximize power dissipation.

3

SHDN

Active-Low Shutdown Input. A logic low reduces the supply current to 10nA. On the MAX8878, a

logic low also causes the output voltage to discharge to GND. Connect to IN for normal operation.

4BP

Reference-Noise Bypass. Bypass with a low-leakage, 0.01

µF ceramic capacitor for reduced noise at

the output.

5

OUT

Regulator Output. Sources up to 150mA. Bypass with a 1

µF (<0.2Ω typical ESR) capacitor to GND