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The CD74HC4538 is a dual retriggerable/resettable precision monostable multivibrator for fixed-voltage timing applications. An external resistor (R_X) and external capacitor (C_X) control the timing and 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 input 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 nontriggerable 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) R_X, C_X; R_MIN is 5 kΩ. C_MIN is 0 pF.