HEF4538B

The HEF4538B is a dual retriggerable-resettable monostable multivibrator. 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, always connected to ground) 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 and will produce an accurate output pulse with a pulse width range of 10 μs to infinity. 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 R_EXT × C_EXT. The linear design techniques in LOCMOS (Local Oxide CMOS) guarantee precise control of the output pulse width. A LOW level at nCD terminates the output pulse immediately. The trigger inputs’ Schmitt trigger action makes the circuit highly tolerant of slower rise and fall times.

It operates over a recommended V_DD power supply range of 3 V to 15 V referenced to V_SS (usually ground). Unused inputs must be connected to V_DD, V_SS, or another input.