Datasheet

10
Power-Down Mode
During a rapid power-down condition, as would occur with a
power-supply short circuit with a poorly filtered power supply,
the energy stored in C
X
could discharge into Pin 2 or 14. To
aviod possible device damage in this mode, when C
X
is ≥
0.5µF, a protection diode with a 1 ampere or higher rating
(1N5395 or equivalent) and a separate ground return for C
X
should be provided as shown in Figure 12.
An alternate protection method is shown in Figure 13, where
a51Ω current-limiting resistor is inserted in series with C
X
.
Note that a small pulse width decrease will occur however,
and R
X
must be appropriately increased to obtain the origi-
nally desired pulse width.
FIGURE 12. RAPID POWER-DOWN PROTECTION CIRCUIT
IN5395
OR
EQUIVALENT
R
X
C
X
≥0.5µF
1(15)
2(14)
V
CC
16
8
+
FIGURE 13. ALTERNATE RAPID POWER-DOWN PROTECTION
CIRCUIT
R
X
C
X
≥0.5µF
1(15)
2(14)
V
CC
16
8
51Ω
CD54HC4538, CD74HC4538, CD54HCT4538, CD74HCT4538