MAX8869

1A, Microcap, Low-Dropout,

Linear Regulator

6

Maxim Integrated

Detailed Description

The MAX8869 features Dual Mode operation, allowing a

fixed output of +5V, +3.3V, +2.5V, +1.8V, or +1.0V, or

adjustable output from +0.8V to +5.0V. The regulators

are guaranteed to supply 1A of continuous output cur-

rent with only 1µF of output capacitance.

As shown in the functional diagram (Figure 1), the

device has a 0.8V reference, error amplifier, MOSFET

driver, P-channel pass transistor, internal feedback

voltage-divider, soft-start function, reset timer, and Dual

The 0.8V reference is connected to the error amplifier’s

inverting input. The error amplifier compares this refer-

ence with the selected feedback voltage and amplifies

the difference. The MOSFET driver reads the error sig-

nal and applies the appropriate drive to the P-channel

transistor. If the feedback voltage is high, the pass tran-

sistor’s gate is pulled up, allowing less current to pass

the feedback voltage has dropped 8% below its

expected level, causing RST to go low.

The output voltage is fed back through either an inter-

nal resistor-divider connected to OUT or an external

resistor network connected to SET. The Dual Mode

is used and the output voltage is regulated to the facto-

ry-preset voltage. Otherwise, the output voltage is set

with the external resistor-divider.

Internal P-Channel Pass Transistor

The MAX8869 features a 1A P-channel MOSFET pass

transistor. Unlike similar designs using PNP pass tran-

sistors, P-channel MOSFETs require no base drive,

which reduces quiescent current. PNP-based regula-

tors also waste considerable current in dropout when

the pass transistor saturates and use high base-drive

currents under large loads. The MAX8869 does not suf-

fer from these problems and consumes only 500µA of

quiescent current even in dropout.

Pin Description

PIN

NAME

FUNCTION

1, 9, 16

N.C.

No Connection. Not internally connected.

2, 3, 4, 5

IN

Regulator Input. Connect to power source (+2.7V to +5.5V). Bypass with 1

µF or greater

capacitor to GND (see Capacitor Selection and Regulator Stability). Connect all IN inputs

together for proper operation.

6

RST

rises to within regulation. Connect a 100k

Ω pullup resistor to OUT to obtain an output voltage.

7

SHDN

Active-Low Shutdown Input. A logic low reduces the supply current to 0.1

µA. Connect SHDN

to IN for normal operation. In shutdown, RST is low and the soft-start capacitor discharges.

8SS

Soft-Start Control. Connect a soft-start capacitor from SS to GND (see Soft-Start Capacitor

Selection). Leave SS open to disable soft-start.

10

GND

Ground. Solder both GND and EP to a large pad or to the circuit-board ground plane to

maximize power dissipation.

11

SET

Voltage-Setting Input. Connect SET to GND for factory-preset output voltage. Connect SET to

an external resistor-divider for adjustable output operation.

12, 13, 14, 15

OUT

Regulator Output. Bypass with a 1

µF or greater low-ESR capacitor to GND (see Capacitor

Selection and Regulator Stability). Connect all OUT outputs together for proper operation.

—EP

Exposed Pad. Connect to a large ground plane to maximize thermal performance. Not

intended as an electrical connection point.