Low-Dropout, 120mA Linear Regulators

6

_______________Detailed Description

The MAX8863/MAX8864 are low-dropout, low-quiescent-

current linear regulators designed primarily for battery-

powered applications. They supply an adjustable 1.25V to

6.5V output or a preselected 2.80V (MAX886_R), 2.84V

(MAX886_S), or 3.15V (MAX886_T) output for load currents

up to 120mA. As illustrated in Figure 1, these devices con-

sist of a 1.25V reference, error amplifier, MOSFET driver, P-

channel pass transistor, Dual Mode™ comparator, and

internal feedback voltage divider.

The 1.25V bandgap reference is connected to the error

amplifier’s inverting input. The error amplifier compares this

reference with the selected feedback voltage and amplifies

the difference. The MOSFET driver reads the error signal

and applies the appropriate drive to the P-channel pass

transistor. If the feedback voltage is lower than the refer-

ence, the pass-transistor gate is pulled lower, allowing more

current to pass 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.

The output voltage is fed back through either an internal

resistor voltage divider connected to the OUT pin, or an

external resistor network connected to the SET pin. The

Dual Mode comparator examines the SET voltage and

selects the feedback path. If SET is below 60mV, internal

feedback is used and the output voltage is regulated to the

preset output voltage. Additional blocks include a current

limiter, reverse battery protection, thermal sensor, and shut-

down logic.

SHUTDOWN

LOGIC

ERROR

AMP

1.25V

REF

P

N

*

OUT

SET

DUAL-MODE

COMPARATOR

60mV

* AUTO-DISCHARGE, MAX8864 ONLY

GND

IN

SHDN

MAX8863

MAX8864

MOS DRIVER

THERMAL

SENSOR

REVERSE

BATTERY

PROTECTION

______________________________________________________________Pin Description

Active-Low Shutdown Input. A logic low reduces the supply current to 0.1nA. On the MAX8864, a logic low

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

SHDN

1

PIN

FUNCTION

NAME

GND

2

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

imize thermal dissipation.

3

Regulator Input. Supply voltage can range from +2.5V to +6.5V. Bypass with 1µF to GND (see

Capacitor

Selection and Regulator Stability).

OUT

4

Regulator Output. Fixed or adjustable from 1.25V to +6.5V. Sources up to 120mA. Bypass with a 1µF, <0.2

Ω

typical ESR capacitor to GND.

IN

SET

5

Feedback Input for Setting the Output Voltage. Connect to GND to set the output voltage to the preset 2.80V

(MAX886_R), 2.84V (MAX886_S), or 3.15V (MAX886_T). Connect to an external resistor divider for

adjustable-output operation.

Figure 1. Functional Diagram