CD54HC4538 Datasheet, PDF (10/11 Pages) Texas Instruments – High Speed CMOS Logic Dual Retriggerable Precision Monostable Multivibrator

CD54HC4538, CD74HC4538, CD74HCT4538
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
a 51Ω 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.
IN5395
OR
R_X
EQUIVALENT
2(14)
C_X
≥ 0.5µF
+
1(15)
V_CC
16
8
R_X
51Ω
C_X
≥ 0.5µF
2(14)
1(15)
V_CC
16
8
FIGURE 12. RAPID POWER-DOWN PROTECTION CIRCUIT
FIGURE 13. ALTERNATE RAPID POWER-DOWN PROTECTION
CIRCUIT
10