AP7217_10 Datasheet, PDF (7/10 Pages) Diodes Incorporated – 500mA CMOS LDO

Timing Diagram
t_RP
20mSec-TYP.
1.8V
AP7217
500mA CMOS LDO
V_IN
VD_OUT
EN
VR_OUT
Application Note
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 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 AP7217 is designed
to have excellent transient response for most applications with a small amount of output capacitance. The AP7217
is stable with any small ceramic output capacitors of 1.0μF 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 AP7217 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_IL and V_IH.
EN=0
EN=1
VR_OUT
0V
3.3V
VD_OUT
Φ
Φ
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 600mA to prevent over-current and to protect the regulator from
damage due to overheating.
AP7217
Document number: DS31292 Rev. 4 - 2
7 of 10
www.diodes.com
April 2010
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