AP7217C

1.25V 600mA CMOS LDO

AP7217C Rev. 3

7 of 9

OCTOBER 2009

DS31424

www.diodes.com

Application Note

Input Capacitor

A 1

µF ceramic capacitor is recommended to connect between IN

and GND pins to decouple input power supply glitch and noise.

The amount of the capacitance may be increased without limit. A

lower ESR (Equivalent Series Resistance) capacitor allows the

use of less capacitance, while higher ESR type requires more

capacitance. This input capacitor must be located as close as

possible to the device to assure input stability and less noise. For

PCB layout, a wide copper trace is required for both IN and GND.

Output Capacitor

The output capacitor is required to stabilize and help the transient

response of the LDO. The AP7217C is designed to have

excellent transient response for most applications with a small

amount of output capacitance. The AP7217C is stable with any

small ceramic output capacitors of 1.0

µF or higher value, and the

temperature coefficients of X7R or X5R type.

Additional

capacitance helps to reduce undershoot and overshoot during

transient. For PCB layout, the output capacitor must be placed as

close as possible to OUT and GND pins, and keep the leads as

short as possible.

ENABLE/SHUTDOWN Operation

The AP7217C (SOP-8L-EP) is turned on by setting the EN pin

high, and is turned off by pulling it low. If this feature is not used,

the EN pin should be tied to IN pin to keep the regulator output on

at all time. To ensure proper operation, the signal source used to

drive the EN pin must be able to swing above and below the

specified turn-on/off voltage thresholds listed in the Electrical

Thermal Considerations

Thermal

Shutdown

Protection

limits

power

dissipation

in

AP7217C. When the operation junction temperature exceeds

140°C, the Over Temperature Protection circuit starts the thermal

shutdown function and turns the pass element off. The pass

element turn on again after the junction temperature cools by

30°C. For continuous operation, do not exceed absolute

maximum operation junction temperature 125°C. The power

dissipation definition in device is:

The maximum power dissipation depends on the thermal

resistance of IC package, PCB layout, the rate of surroundings

airflow and temperature difference between junctions to ambient.

The maximum power dissipation can be calculated by following

formula:

to ambient thermal resistance.

Current Limit Protection

When output current at OUT pin is higher than current limit

threshold, the current limit protection will be triggered and clamp

the

output

current

to

approximately

750mA

to

prevent

over-current and to protect the regulator from damage due to

overheating.

Short circuit protection

200mV, short circuit protection will be triggered and clamp the

output current to approximately 70mA.

Vin

Vout

C

Co

ESR

Iin

IN

AP7217C

GND

Iq

OUT

Iout