M74HC423 查看數據表（PDF） - STMicroelectronics
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M74HC423 Datasheet PDF : 11 Pages
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TIMING CHART
M74HC423
BLOCK DIAGRAM
1) Cx, Rx, Dx are external components.
(2) Dx is a clamping diode.
The external capacitor is charged to Vcc in the stand-by-state, i.e. no trigger. When the supply voltage is turned off Cx is di scharged mainly
trough an internal parasitic diode(see figures). If Cx is sufficiently large and Vcc decreases rapidly, there will be some possibility of damaging
the I.C. with a surge current or latch-up. If the voltage supply filter capacitor is large enough and Vcc decrease slowly, the surge current is
automatically limited and damage to the I.C. 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 Vcc can be calculated as follows :
tf > (Vcc - 0.7) x Cx/20mA
In cases where tf is too short an external clamping diode is required to protect the I.C. from the surge current.
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