AP138

300mA Low-Noise CMOS LDO

Anachip Corp.

www.anachip.com.tw

Rev. 1.0 Oct 29, 2004

6/7

Function Description

The AP138 of CMOS regulators contain a PMOS

pass transistor, voltage reference, error amplifier,

over-current protection, thermal shutdown.

The P-channel pass transistor receives data from

the error amplifier, over-current protection, and

thermal protection 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 150

300mA. During thermal shutdown, the output

voltage remains low. Normal operation is restored

when the junction temperature drops below 120

The AP138 switches from voltage mode to current

mode when the load exceeds the rated output

current. This prevents over-stress.

Enable

The enable pin normally floats high. When actively,

pulled low, the PMOS pass transistor shut off, and

all internal circuits are powered down. In this state,

the quiescent current is less than 2µA. This pin

behaves much like an electronic switch.

External Capacitor

The AP138 is stable with a low ESR output

capacitor to ground of 1.0µF or greater. It can keep

stable even with higher ESR capacitors. A second

capacitor is recommended between the input and

ground to stabilize VIN. The input capacitor should

be larger than 0.1µF to have a beneficial effect. All

capacitors should be placed in close proximity to

the pins. A “quiet” ground termination is desirable.

Marking Information

X : Identification code

(See Appendix)

Y : Year: 0-9

W : Week: A~Z: 01~26

a~z : 27~52

. : 53

SOT23-5L

3 8 X Y W

12

3

4

5

Appendix

Identification

Code

Output version

D

AP138-1.8V

K

AP138-2.5V

N

AP138-2.8V

P

AP138-3.0V

S

AP138-3.3V