74AHC123APW View Datasheet(PDF) - Philips Electronics

Part Name

Description

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74AHC123APW

Dual retriggerable monostable multivibrator with reset

Philips Electronics 

Philips Semiconductors

Dual retriggerable monostable multivibrator

with reset

Product specification

74AHC123A;

74AHCT123A

FEATURES

• ESD protection:

HBM EIA/JESD22-A114-A exceeds 2000 V

MM EIA/JESD22-A115-A exceeds 200 V

CDM EIA/JESD22-C101 exceeds 1000 V

• All inputs have Schmitt-trigger actions

• Inputs accept voltages higher than VCC

• For AHC only: operates with CMOS input levels

• For AHCT only: operates with TTL input levels

• Specified from −40 to +85 °C and −40 to +125 °C

• DC triggered from active HIGH or active LOW inputs

• Retriggerable for very long pulses up to 100% duty

factor

• Direct reset terminates output pulse

• Output capability: standard (except for nREXT/CEXT).

DESCRIPTION

The 74AHC/AHCT123A 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 74AHC/AHCT123A are dual retriggerable monostable

multivibrators with output pulse width control by three

methods. The basic pulse time is programmed by

selection of an external resistor (REXT) and capacitor

(CEXT). The external resistor and capacitor are normally

connected as shown in Fig.6.

Once triggered, the basic output pulse width may be

extended by retriggering the gated active LOW-going edge

input (nA) or the active HIGH-going edge input (nB).

By repeating this process, the output pulse period

(nQ = HIGH, nQ = LOW) can be made as long as desired.

Alternatively an output delay can be terminated at any time

by a LOW-going edge on input nRD, which also inhibits the

triggering.

An internal connection from nRD to the input gate makes it

possible to trigger the circuit by a positive-going signal at

input nRD as shown in the function table. Figs 8 and 9

illustrate pulse control by retriggering and early reset. The

basic output pulse width is essentially determined by the

value of the external timing components REXT and CEXT.

When CEXT ≥ 10 nF, the typical output pulse width is

defined as: tW = REXT × CEXT where tW = pulse width in ns;

REXT = external resistor in kΩ; CEXT = external capacitor

in pF. Schmitt-trigger action at all inputs makes the circuit

highly tolerant to slower input rise and fall times. The ‘123’

is identical to the ‘423’ but can be triggered via the reset

input.

2000 Mar 15

2

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