Diodes AP7217D - Manual (Page 7)

AP7217D
1.2V 600mA CMOS LDO
AP7217D Rev. 2 7 of 9 FEBRUARY 2009
www.diodes.com © Diodes Incorporated
Application Information
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 AP7217D is designed to have
excellent transient response for most applications with a small
amount of output capacitance. The AP7217D 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.
Thermal Considerations
Thermal Shutdown Protection limits power dissipation in
AP7217D. When the operation junction temperature exceeds
150°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 recommend
maximum operation junction temperature 125°C. The power
dissipation definition in device is:
P
D
= (V
IN
− V
OUT
) x I
OUT
+ V
IN
x I
Q
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:
P
D(MAX)
= ( T
J(MAX)
- TA ) / θ
JA
Where T
J(MAX)
is the maximum operation junction temperature
125°C, T
A
is the ambient temperature and the θ
JA
is the junction
to ambient thermal resistance.
V
IN
V
OUT
C
IN
C
OUT
ESR
I
IN
IN
AP7217D
GND
Iq
OUT
I
OUT
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 850mA to prevent
over-current and to protect the regulator from damage due to
overheating.
Short circuit protection
When V
OUT
pin is shorted to GND or V
OUT
voltage is less than
200mV, short circuit protection will be triggered and clamp the
output current to approximately 200mA.