AME8808LECS datasheet(6/11 Pages) AME

6 / 11 page

Analog Microelectronics, Inc.

750mA CMOS LDO

AME8808

n Detailed Description

The AME8808 family of CMOS regulators contain a

PMOS pass transistor, voltage reference, error amplifier,

over-current protection, and thermal shutdown.

The P-channel pass transistor receives data from the

error amplifier, over-current shutdown, and thermal pro-

tection circuits. During normal operation, the error am-

plifier compares the output voltage to a precision refer-

ence. Over-current and Thermal shutdown circuits be-

come active when the junction temperature exceeds

150oC, or the current exceeds 750mA. During thermal

shutdown, the output voltage remains low. Normal op-

eration is restored when the junction temperature drops

below 120oC.

The AME8808 switches from voltage mode to current mode

when the load exceeds the rated output current. This

prevents over-stress. The AME8808 also incorporates

current foldback to reduce power dissipation when the

output is short circuited. This feature becomes active

when the output drops below 0.8 volts, and reduces the

current flow by 65%. Full current is restored when the

voltage exceeds 0.8 volts.

n External Capacitors

The AME8806/8809 is stable with an output capacitor

to ground of 2.2

µF or greater. Ceramic capacitors have

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

Conversely, Aluminum Electrolytic capacitors exhibit

the highest ESR, resulting in the poorest 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 over-

all cost.

A second capacitor is recommended between the input

and ground to stabilize Vin. The input capacitor should

be at least 0.1

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 normally floats high. When actively,

pulled low, the PMOS pass transistor shuts off, and all

internal circuits are powered down. In this state, the

quiescent current is less than 1

µA. This pin behaves

much like an electronic switch.

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