Diodes AP7167 Manuel d'utilisateur télécharger pdf (Page 9)

AP7167

1.2A LOW DROPOUT REGULATOR WITH POK

AP7167

Document number: DS31252 Rev. 7 - 2

9 of 14

www.diodes.com

September 2010

Application Notes

Input Capacitor

A 1μF 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 should 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 AP7167 is designed to

have excellent transient response for most applications

with a small amount of output capacitance. The AP7167 is

stable for all available types and values of output

capacitors

≥ 4.7μF. The device is also stable with multiple

capacitors in parallel, which can be of any type of value.

Additional capacitance helps to reduce undershoot and

overshoot during transient. This capacitor should be

placed as close as possible to OUT and GND pins for

optimum performance.

Adjustable Operation

The AP7167 provides output voltage from 0.8V to 5.0V

through external resistor divider as shown below.

GND

OUT

Enable

OUT

POK

100kOhm

AP7167

OUT

The output voltage is calculated by:

⎟

⎠

⎞

⎜

⎝

⎛

REF

OUT

Where V

REF

=0.8V (the internal reference voltage)

Rearranging the equation will give the following equation

to find the approximate resistor divider values:

⎟

⎠

⎞

⎜

⎝

⎛

−= 1

REF

OUT

To maintain the stability of the internal reference voltage,

needs to be kept smaller than 250kΩ.

No Load Stability

Other than external resistor divider, no minimum load is

required to keep the device stable. The device will remain

stable and regulated in no load condition.

ENABLE/SHUTDOWN Operation

The AP7167 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 Characteristics section

under V

and V

POWER-OK

The Power-Ok (POK) pin is an active high open-drain

output. It can be connected to any 5.5V or lower rail

through an external pull-up resistor. The recommended

sink current of POK pin is up to 4mA, so the pull-up

resistor for POK should be in the range of 10kΩ to 1MΩ. If

output voltage monitoring is not needed, the POK pin can

be left floating.

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 1.6A (1.2A min)

to prevent over-current and to protect the regulator from

damage due to overheating.

Short Circuit Protection

When OUT pin is short-circuited to GND or OUT pin

voltage is less than 200mV, short circuit protection will be

triggered and clamp the output current to approximately

750mA. This feature protects the regulator from over-

current and damage due to overheating.

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Diodes AP7167 Manuel d'utilisateur Page 9

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