AME8821 datasheet(8/15 Pages) AME

8 / 15 page

AME, Inc.

250mA Hi-PSRR, Low-Quiescent LDO

with In-Rush Current Control

For USB Application

AME8821

Rev.A.01

n Detail Description

The AME8821 family of CMOS regulators contain a

PMOS pass transistor, voltage reference, error ampli-

fier, over-current protection, and thermal shutdown func-

tion.

The P-channel pass transistor receives data from

the error amplifier, over-current limit, and thermal pro-

tection circuits. During normal operation, the error

amplifier compares the output voltage to a precision

reference. Over-current and thermal shutdown circuits

become active when the junction temperature exceeds

150oC, or the current exceeds about 350mA. During

thermal shutdown, the output voltage remains low.

Normal operation is restored when the junction tem-

perature drops below 130oC.

The AME8821 switches from voltage mode to cur-

rent mode when the load exceeds the rated output

current. This prevents over-stress.

n External Capacitors

The AME8821 is stable with an output capacitor to

ground of 4.7

µF or greater. Ceramic capacitors have

the lower ESR, and will offer the best AC performance.

Conversely, Aluminum Electrolytic capacitors exhibit

the higher ESR, resulting in the poor AC response.

Unfortunately, large value ceramic capacitors are com-

paratively expensive. One option is to parallel a 0.1

µF

ceramic capacitor with a 10

µF Aluminum Electrolytic.

The benefit is low ESR, high capacitance, and low overall

cost.

A second capacitor is recommended between the

input and ground to stabilize V

IN. The input capacitor

should be at least 1

µF to have a beneficial effect. All

capacitors should be placed in close proximity to the

pins. A

“Quiet” ground termination is desirable. This

can be achieved with a

“Star”connection

n Enable

The Enable pin is optional. EN for active high en-

able, ENB for active low enable. When disable the

Enable Pin EN = 0, ENB = V

IN, the PMOS pass tran-

sistor shuts off, and all internal circuits are powered

down. In this state, the standby current is less than

µA.

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