December 1990

2

Philips Semiconductors

Product specification

Dual non-retriggerable monostable

multivibrator with reset

74HC/HCT221

FEATURES

• Pulse width variance is typically less than ± 5%

• Pin-out identical to “123”

• Overriding reset terminates output pulse

• nB inputs have hysteresis for improved noise immunity

GENERAL DESCRIPTION

The 74HC/HCT221 are high-speed Si-gate CMOS devices

and are pin compatible with low power Schottky TTL

(LSTTL). They are specified in compliance with JEDEC

standard no. 7A.

The 74HC/HCT221 are dual non-retriggerable monostable

multivibrators. Each multivibrator features an active

LOW-going edge input (nA) and an active HIGH-going

edge input (nB), either of which can be used as an enable

input.

Pulse triggering occurs at a particular voltage level and is

not directly related to the transition time of the input pulse.

Schmitt-trigger input circuitry for the nB inputs allow

jitter-free triggering from inputs with slow transition rates,

providing the circuit with excellent noise immunity.

Once triggered, the outputs (nQ, nQ) are independent of

further transitions of nA and nB inputs and are a function

of the timing components. The output pulses can be

terminated by the overriding active LOW reset inputs

output pulse.

Pulse width stability is achieved through internal

temperature. In most applications pulse stability will only

be limited by the accuracy of the external timing

components.

The output pulse width is defined by the following

relationship:

Pin assignments for the “221” are identical to those of the

“123” so that the “221” can be substituted for those

products in systems not using the retrigger by merely

QUICK REFERENCE DATA

Notes

SYMBOL

PARAMETER

CONDITIONS

TYPICAL

UNIT

HC

HCT

propagation delay

2932ns

3536ns

input capacitance

3.5

3.5

pF

power dissipation capacitance per package notes 1 and 2

90

96

pF