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12-11
SPECIAL OPERATING MODES
Figure 12-5. Typical Voltage on the RPD Pin While Exiting Powerdown
When selecting the capacitor, determine the worst-case discharge time needed for the oscillator
to stabilize, then use this formula to calculate an appropriate value for C
1
.
where:
C
1
is the capacitor value, in farads
T
DIS
is the worst-case discharge time, in seconds
I is the discharge current, in amperes
V
t
is the threshold voltage
NOTE
If powerdown is re-entered and exited before C
1
charges to V
CC
, it will take
less time for the voltage to ramp down to the threshold. Therefore, the device
will take less time to exit powerdown.
1
2
3
4
5
200 µA C
1
Discharge
Code Execution
Resumes
EXTINT
x
Time, ms
2 4 6 8 10 12 14 16 18 20 22
RPD, Volts
A2385-02
V
CC
= 5 V
V
CC
= 3 V
.8 V
1.2 V
3 V
5 V
C
1
T
DIS
I×
V
t
--------------------
=