1. General description
The 74HC4538; 74HCT4538 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 74HC4538; 74HCT4538 are dual retriggerable-resettable monostable multivibrators.
Each multivibrator has an active LOW trigger/retrigger input (nA), an active HIGH
trigger/retrigger input (nB), an overriding active LOW direct reset input (nCD), an output
(nQ) and its complement (nQ), and two pins (nREXT/CEXT and nCEXT) for connecting
the external timing components C
EXT
and R
EXT
. Typical pulse width variation over the
specified temperature range is ±0.2 %.
The multivibrator may be triggered by either the positive or the negative edges of the input
pulse. The duration and accuracy of the output pulse are determined by the external
timing components C
EXT
and R
EXT
. The output pulse width (t
W
) is equal to
0.7 × R
EXT
× C
EXT
. The linear design techniques guarantee precise control of the output
pulse width. A LOW level at nCD terminates the output pulse immediately. Schmitt trigger
action on pins nA and nB makes the circuit highly tolerant of slower rise and fall times.
2. Features
n Tolerant of slow trigger rise and fall times
n Separate reset inputs
n Triggering from falling or rising edge
n Multiple package options
n ESD protection:
u HBM JESD22-A114E exceeds 2000 V
u MM JESD22-A115-A exceeds 200 V
n Specified from −40 °Cto+85°C and from −40 °C to +125 °C
74HC4538; 74HCT4538
Dual retriggerable precision monostable multivibrator
Rev. 03 — 8 June 2009 Product data sheet
