Datasheet

September 1993 2
Philips Semiconductors Product specification
Dual retriggerable precision monostable
multivibrator
74HC/HCT4538
FEATURES
• Separate reset inputs
• Triggering from leading or trailing edge
• Output capability: standard
• I
CC
category: MSI
• Power-on reset on-chip
GENERAL DESCRIPTION
The 74HC/HCT4538 are high-speed Si-gate CMOS
devices and are pin compatible with “4538” of the “4000B”
series. They are specified in compliance with JEDEC
standard no. 7A.
The 74HC/HCT4538 are dual retriggerable-resettable
monostable multivibrators. Each multivibrator has an
active LOW trigger/retrigger input (n
A
0
), an active HIGH
trigger/retrigger input (nA
1
) , an overriding active LOW
direct reset input (nR
D
), an output (nQ) and its complement
(nQ), and two pins (nC
TC
and nRC
TC
) for connecting the
external timing components C
t
and R
t
. Typical pulse width
variation over temperature range is ± 0.2%.
The “4538” 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
t
and R
t
. The output pulse
width (T) is equal to 0.7 × R
t
× C
t
. The linear design
techniques guarantee precise control of the output pulse
width.
A LOW level at nR
D
terminates the output pulse
immediately.
Schmitt-trigger action in the trigger inputs makes the circuit
highly tolerant to slower rise and fall times.
QUICK REFERENCE DATA
GND = 0 V; T
amb
= 25 °C; t
r
= t
f
= 6 ns
Notes
1. C
PD
is used to determine the dynamic power dissipation (P
D
in µW):
P
D
= C
PD
× V
CC
2
× f
i
+∑(C
L
× V
CC
2
× f
o
) +
+ 0.48 × C
EXT
× V
CC
2
× f
o
+ D × 0.8 × V
CC
where:
f
i
= input frequency in MHz
f
o
= output frequency in MHz
∑ (C
L
× V
CC
2
× f
o
) = sum of outputs
C
L
= output load capacitance in pF
V
CC
= supply voltage in V
D = duty factor in %
C
EXT
= timing capacitance in pF
2. For HC the condition is V
I
= GND to V
CC
For HCT the condition is V
I
= GND to V
CC
− 1.5 V
ORDERING INFORMATION
See
“74HC/HCT/HCU/HCMOS Logic Package Information” .
SYMBOL PARAMETER CONDITIONS
TYPICAL
UNIT
HC HCT
t
PHL
/ t
PLH
propagation delay nA
0
,nA
1
to nQ, nQC
L
= 15 pF; V
CC
= 5 V 27 30 ns
C
I
input capacitance 3.5 3.5 pF
C
PD
power dissipation capacitance per multivibrator notes 1 and 2 136 138 pF