1. General description
The 74HCT4538 is a dual retriggerable-resettable monostable multivibrator. Each multivibrator has
two trigger/retrigger inputs (nA and nB), a direct reset input (nCD), two complementary outputs (nQ
and nQ), and two pins (nREXT/CEXT and nCEXT) for connecting the external timing components
CEXT and REXT. Typical pulse width variation over temperature range is ± 0.2 %. The device
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 CEXT and
REXT. The output pulse width (TW) is equal to 0.7 × REXT × CEXT. 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 in the trigger inputs makes the circuit highly tolerant to
slower rise and fall times. Inputs include clamp diodes. This enables the use of current limiting
resistors to interface inputs to voltages in excess of VCC.
2. Features and benefits
• Tolerant of slow trigger rise and fall times
• High noise immunity
• Separate reset inputs
• Triggering from falling or rising edge
• Complies with JEDEC standard no. 7A
• Wide supply voltage range from 4.5 to 5.5 V
• CMOS low power dissipation
• TTL input levels
• Latch-up performance exceeds 100 mA per JESD 78 Class II Level B
• ESD protection:
• HBM JESD22-A114F exceeds 2000 V
• MM JESD22-A115-A exceeds 200 V
• Specified from -40 °C to +85 °C and from -40 °C to +125 °C