74LS221 IC-Dual Non-Retrigger able-Monostable Multivibrator With Reset

The 74LS221 (74221) is a dual non-retrigger able monostable multivibrator that provides two independent one-shot circuits in a single 16-pin package. Each channel accepts both negative-transition and positive-transition trigger inputs, enabling flexible triggering schemes for diverse digital designs. Schmitt-triggered B inputs and internal latching give the device excellent noise immunity and predictable triggering behaviour.

Pulse width is set by external timing components (Rext and Cext) and follows the approximate relationship tw ≈ 0.7·Rext·Cext, allowing pulse durations from tens of nanoseconds up to milliseconds depending on component values. Once a pulse is initiated the output remains independent of further A/B input transitions (non-retriggerable), while an overriding clear input (CLR) can terminate the pulse early when required. Timing stability is ensured across supply and temperature ranges by internal compensation.

The device offers TTL-compatible rise/fall times and totem-pole outputs, and is available in multiple packages (PDIP, SOIC, SSOP, CDIP, etc.), making it straightforward to integrate in through-hole and surface-mount assemblies. Common uses include reset generation, pulse stretching, debouncing, and timing control where a compact, reliable single-shot solution is needed.