The ’HC4538 and ’HCT4538 are dual retriggerable/resettable monostable precision multivibrators for fixed voltage timing applications. An external resistor (R_X) and an external capacitor (C_X) control the timing and the accuracy for the circuit. Adjustment of R_X and C_X provides a wide range of output pulse widths from the Q and Q\ terminals. The propagation delay from trigger input-to-output transition and the propagation delay from reset input-to-output transition are independent of R_X and C_X.

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 V_CC. 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 (. C_MIN is 0pF.