User`s manual

PK2200 Power Management s 81
The ratio of your power supplys output capacitors value to your circuits
current draw determines the actual duration of the holdup-time interval, t
H
.
Figure C-2. Power Fail Sequence of Events
This setup can fail when multiple power fluctuations happen rapidly  a
common occurrence in the real world. If the PK2200s Z180 processor
receives multiple /NMIs, it overwrites an internal register, making a
correct return from the first /NMI impossible. Also, depending on the
number of fluctuations of the raw DC input (and hence, the number of
stacked /NMIs), the processors stack could overflow, corrupting your
programs code or data.
When the Z180 senses an NMI, it saves the program counter (PC) on its
processor stack. It copies the maskable interrupt flag, IEF1, to IEF2 and
zeroes IEF1. The Z180 restores IEF2s saved state information when it
executes a RETN (Return from Nonmaskable Interrupt) instruction.
1.0
2.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
I
Unregulated
DC
Regulated
+5V
691
Asserts
PFO
691
Asserts
RESET
691
Ceases
Operation
t
H
Power
Fails
VOLTS
TIME
C
Slope =
C/-I
Dropout
Voltage