Diodes AP7217A - Manual (Page 7)

AP7217A
3.3V 600mA CMOS LDO
AP7217A Rev. 3 7 of 10 OCTOBER 2009
DS31423 www.diodes.com © Diodes Incorporated
Timing Diagram
200mSec-TYP.
V
IN
VD
OUT
EN
VR
OUT
1.6V
t
RP
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 AP7217A 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 1.0
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 AP7217A 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
.
VR
OUT
VD
OUT
EN=0 0V Φ
EN=1 3.3V Φ
Thermal Considerations
Thermal Shutdown Protection limits power dissipation in
AP7217A. 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
40°C. For continuous operation, do not exceed absolute
maximum operation junction temperature 125°C. The power
dissipation definition in device is:
P
D
= (V
IN
− V
OU
T) 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 junction 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.