There is a rapid power-down condition when a power supply short circuit or
when there is a poorly filtered power supply. CD4538B series CMOS Dual Precision
Monostable Vibrator has the Power-Down Mode feature to avoid possible device
damage in this mode.
As seen in the circuit diagram, in such mentioned condition above, the energy stored in Cx could discharge into Pin 2 or 14 of the CD4538B IC. In order to avoid device damage when Cx is bigger than 0.5uF, a 1A or higher (1N5395 or equivalent) of protection diode and a separate ground return for Cx should be provided.
See the CD4538B datasheet for completed CD4538B Rapid Power Down Protection Circuit Diagram (source: hqew.net).
As seen in the circuit diagram, in such mentioned condition above, the energy stored in Cx could discharge into Pin 2 or 14 of the CD4538B IC. In order to avoid device damage when Cx is bigger than 0.5uF, a 1A or higher (1N5395 or equivalent) of protection diode and a separate ground return for Cx should be provided.
See the CD4538B datasheet for completed CD4538B Rapid Power Down Protection Circuit Diagram (source: hqew.net).
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