AMC7635

Copyright

© 2007 ADDtek Corp.

7

DD078_A

-- SEPTEMBER 2007

APPLICATION INFORMATION

AMC7635

GND

1uF

2.2uF

GND

BP

EN

1000pF

Detailed Description

The AMC7635 CMOS low dropout regulator contains a PMOS pass transistor, a voltage reference, an error

amplifier, over-current protection, and thermal shutdown circuit.

The P-channel pass transistor receives data from the error amplifier, over-current shutdown, and thermal

protection circuits. During normal operation, the error amplifier compares the output voltage to a precision

reference. T hermal shutdown and over-current circuits become active when the junction temperature exceeds

150℃, or the current exceeds 300mA. During thermal shutdown, the output voltage remains low. Normal operation

is restored when the junction temperature drops below 120℃.

External Capacitors

The AMC7635 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 comparatively

expensive. One option is to parallel a 0.1

µF ceramic capacitor with a 10µF Aluminum Electrolytic. The benefit is

low ESR, high capacitance, and low over-all cost.

at least 0.1

µF to have a beneficial effect.

A third capacitor can be connected between the BP pin and GND. This capacitor can be a low cost Polyester

Film variety between the value of 0.001 ~ 0.01

µF. A larger capacitor improves the AC ripple rejection, but also

makes the output come up slowly. This "Soft" turn-on is desirable in some applications to limit turn-on surges.

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.

EN

The EN pin is normally pulled to high. When shutdown, 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.