74VHC221AMTC(2007) データシートの表示（PDF） - Fairchild Semiconductor

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74VHC221AMTC
(Rev.:2007)

Dual Non-Retriggerable Monostable Multivibrator

Fairchild Semiconductor 

Connection Diagram

Block Diagrams

Logic Symbol

IEEE/IEC

Truth Table

Inputs

A B CLR

H

H

XL

H

HX

H

L

H

LH

XX

L

Outputs

QQ

LH

LH

LH

Function

Output Enable

Inhibit

Inhibit

Output Enable

Output Enable

Reset

H = HIGH Voltage Level

L = LOW Voltage Level

= HIGH-to-LOW Transition

= LOW-to-HIGH Transition

X = Don’t Care

©1994 Fairchild Semiconductor Corporation

74VHC221A Rev. 1.2

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 possibil-

ity 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 para-

sitic diode is ±20 mA. 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 condi-

tion, an external clamping diode (Dx) is needed to

protect the IC from rush current.

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