AP139

300mA LOW-NOISE CMOS LDO

AP139 Rev. 6

5 of 7

FEBRUARY 2009

www.diodes.com

Typical Performance Characteristics

(Continued)

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

1.0E+00

1.0E+01

1.0E+02

1.0E+03

1.0E+04

1.0E+05

1.0E+06

Power Supply Rejection Ratio

Frequency (Hz)

100mA

10mA

1mA

BP=0

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

1.5

1.8

2

2.5

2.8

3

3.3

3.5

Vout Vs Current Limit

Vcc=5V

Vout (V)

0

50

100

150

200

250

300

350

400

3 .5

4

4.5

5

5.5

6

V c c V s S hor t C ur r e nt

V cc ( V )

T op t o bot tom

V out= 1 .5V

V out= 1 .8V

V out= 2 .5V

V out= 3 .3V

Functional Description

The AP139 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. The over-current and thermal

shutdown circuits become active when the junction temperature

exceeds 130

shutdown, the output voltage remains low. Normal operation is

restored when the junction temperature drops below 110

The AP139 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 shuts off, and all internal circuits are

powered down. In this state, the quiescent current is less than

2

μA. This pin behaves much like an electronic switch.

External Capacitor

The AP139 is stable with a low ESR output capacitor to ground of

1.0

μF or greater. It can keep stable even with higher ESR

capacitors. A second capacitor is recommended between the

larger than 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.