74VHC123AMTC(2007) View Datasheet(PDF) - Fairchild Semiconductor

Part Name

Description

Manufacturer

74VHC123AMTC
(Rev.:2007)

Dual Retriggerable Monostable Multivibrator

Fairchild Semiconductor 

Block Diagrams

Note A: Cx, Rx, Dx are external Capacitor, Resistor, and Diode, respectively.

Note B: External clamping diode, Dx;

External capacitor is charged to VCC level in the wait state, i.e. when no trigger is applied.

If the supply voltage is turned off, Cx discharges mainly through the internal (parasitic) diode. If Cx is sufficiently large

and VCC drops rapidly, there will be some possibility of damaging the IC through in rush current or latch-up. If the

capacitance of the supply voltage filter is large enough and VCC drops slowly, the in rush current is automatically

limited and damage to the IC is avoided.

The maximum value of forward current through the parasitic diode is ±20mA. In the case of a large Cx, the limit of fall

time of the supply voltage is determined as follows:

tf ≥ (VCC –0.7) Cx / 20mA

(tf is the time between the supply voltage turn off and the supply voltage reaching 0.4 VCC)

In the event a system does not satisfy the above condition, an external clamping diode (Dx) is needed to protect the IC

from rush current.

©1993 Fairchild Semiconductor Corporation

74VHC123A Rev. 1.2

3

www.fairchildsemi.com

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