AME8861 Datasheet, PDF(5/9 Page) Analog Microelectronics

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AME8861 Datasheet, PDF (5/9 Pages) Analog Microelectronics – 600mA CMOS LDO

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AME, Inc.

AME8861

600mA CMOS LDO

n Detailed Description

The AME8861 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 ampli-

fier compares the output voltage to a precision reference.

Over-current and Thermal shutdown circuits become ac-

tive when the junction temperature exceeds 150oC, or

the current exceeds 600mA. During thermal shutdown,

the output voltage remains low. Normal operation is re-

stored when the junction temperature drops below 120oC.

The AME8861 switches from voltage mode to current

mode when the load exceeds the rated output current.

This prevents over-stress. The AME8861 also incorpo-

rates current foldback to reduce power dissipation when

the output is short circuited. This feature becomes ac-

tive 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.

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 qui-

escent current is less than 1ÂµA. This pin behaves much

like an electronic switch.

n External Capacitors

The AME8861 is stable with an output capacitor to

ground of 2.2ÂµF or greater. Ceramic capacitors have the

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

versely, Aluminum Electrolytic capacitors exhibit the high-

est ESR, resulting in the poorest AC response. Unfortu-

nately, large value ceramic capacitors are comparatively

expensive. One option is to parallel a 0.1ÂµF ceramic

capacitor with a 10ÂµF Aluminum Electrolytic. The benefit

is low ESR, high capacitance, and low overall cost.

A second capacitor is recommended between the in-

put and ground to stabilize Vin. The input capacitor should

be at least 0.1ÂµF to have a beneficial effect.

A third capacitor can be connected between the BY-

PASS pin and GND. This capacitor can be a low cost

Polyester Film variety between the value of 0.001 ~

0.01ÂµF. A larger capacitor improves the AC ripple rejec-

tion, but also makes the output come up slowly. This

"Soft" turn-on is desirable in some applications to limit

turn-on surges.

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