Features
• Retriggerable/Resettable Capability
• Trigger and Reset Propagation Delays Independent of
RX, CX
• Triggering from the Leading or Trailing Edge
• Q and Q Buffered Outputs Available
• Separate Resets
• Wide Range of Output Pulse Widths
• Schmitt Trigger Input on A and B Inputs
• Retrigger Time is Independent of CX
• Fanout (Over Temperature Range)
- Standard Outputs . . . . . . . . . . . . . . . 10 LSTTL Loads
- Bus Driver Outputs . . . . . . . . . . . . . 15 LSTTL Loads
• Wide Operating Temperature Range . . . -55oC to 125oC
• Balanced Propagation Delay and Transition Times
• Significant Power Reduction Compared to LSTTL
Logic ICs
• HC Types
- 2V to 6V Operation
- High Noise Immunity: NIL = 30%, NIH = 30% of VCC
at VCC = 5V
• HCT Types
- 4.5V to 5.5V Operation
- Direct LSTTL Input Logic Compatibility,
VIL= 0.8V (Max), VIH = 2V (Min)
- CMOS Input Compatibility, Il ≤ 1μA at VOL, VOH

Description
The ’HC4538 and ’HCT4538 are dual
retriggerable/resettable monostable precision multivibrators
for fixed voltage timing applications. An external resistor
(RX) and an external capacitor (CX) control the timing and
the accuracy for the circuit. Adjustment of RX and CX
provides a wide range of output pulse widths from the Q and
Q terminals. The propagation delay from trigger input-tooutput
transition and the propagation delay from reset inputto-
output transition are independent of RX and CX.
Leading-edge triggering (A) and trailing edge triggering (B)
inputs are provided for triggering from either edge of the
input pulse. An unused “A” input should be tied to GND and
an unused B should be tied to VCC. On power up the IC is
reset. Unused resets and sections must be terminated. In
normal operation the circuit retriggers on the application of
each new trigger pulse. To operate in the non-triggerable
mode Q is connected to B when leading edge triggering (A)
is used or Q is connected to A when trailing edge triggering
(B) is used. The period (τ) can be calculated from τ = (0.7)
RX, CX; RMIN is 5kΩ. CMIN is 0pF.