m74hc4538 STMicroelectronics, m74hc4538 Datasheet - Page 4

• Manufacturer Part Number: m74hc4538
• Description: Dual Retriggerable Monostable Multivibrator
• Manufacturer: STMicroelectronics

Pin connection and IEC logic symbols
4/18
Figure 4.
Figure 5.
1. Cx, Rx, Dx are external components.
2. Dx is a clamping diode.
The external capacitor is charged to V
turned off Cx is discharged mainly through an internal parasitic diode (see figures). If Cx is sufficiently large
and V
up. If the voltage supply filter capacitor is large enough and V
automatically limited and damage to the IC is avoided. The maximum forward current of the parasitic diode
is approximately 20 mA. In cases where Cx is large the time taken for the supply voltage to fall to 0.4 V
can be calculated as follows: t
In cases where t
current.
CC
decreases rapidly, there will be some possibility of damaging the IC with a surge current or latch-
Timing chart
Block diagram
f
is too short an external clamping diode is required to protect the IC from the surge
f
> (V
CC
CC
- 0.7) x Cx/20 mA.
in the standby state, i.e. no trigger. When the supply voltage is
CC
decreases slowly, the surge current is
M74HC4538
CC