AME8845AECT250Z datasheet(11/19 Pages) AME

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AME

AME8845

3A CMOS LDO

Rev.C.03

The AME8845 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 140oC, or

the current exceeds 4.5A. During thermal shutdown, the

output voltage remains low. Normal operation is restored

when the junction temperature drops below 110oC.

The AME8845 behaves like a current source when the

load reaches 4.5A. However, if the load impedance drops

below 0.3 ohms, the current drops back to 600mA to

prevent excessive power dissipation. Normal operation

is restored when the load resistance exceeds 0.75 ohms.

n Detailed Description

n External Capacitors

The AME8845 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. 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 0.1

µF ceramic ca-

pacitor with a 10

µF 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 0.1

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.

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