74LS221 74221 IC-Dual Non-Retriggerable-Monostable Multivibrator With Reset
The 74LS221 (74221) is a dual non-retriggerable 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 behavior.
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.
Features:
- Dual non-retriggerable monostable one-shot in a single 16-pin package.
- Accepts negative-transition and positive-transition triggers for flexible operation.
- Schmitt-triggered B inputs for jitter-free triggering from slow edges.
- Overriding clear (CLR) input to terminate output pulses early.
- Pulse width set by external R and C with formula tw ≈ 0.7·Rext·Cext.
- Jitter-free operation over wide timing component ranges and temperature.
- TTL-compatible outputs with totem-pole drive.
- Available in PDIP, SOIC, SSOP, CDIP and other package options.
Specifications:
| Parameter: | Value: |
|---|---|
| Function: | Dual non-retriggerable monostable multivibrator |
| Supply voltage (VCC): | Recommended 5 V (typical operating ranges shown: 4.75–5.25 V for 74/74221 variants) |
| Typical pulse-width relation: | tw ≈ 0.7 · Rext · Cext (user-selected external components) |
| External timing resistor (Rext): | Typical recommended range 1.4 kΩ to tens of kΩ (device/version dependent) |
| External timing capacitance (Cext): | 0 to 1000 µF (depends on required range; jitter-free over many decades) |
| Input thresholds (B input): | VT+ / VT− values given in datasheet (Schmitt thresholds for B input) |
| Output type: | TTL totem-pole outputs |
| Operating temperature: | Depends on version: commercial 0°C to +70°C, military versions extend wider |
| Package options: | PDIP (N), SOIC (D), SSOP (DB), CDIP (J), LCCC (FK) |
Pinout Diagram:
Footprint Diagram:
Applications:
- Reset generation and watchdog timing.
- Pulse stretching and debouncing.
- One-shot timing in control logic.
- Event timing and gating in digital systems.
- Edge detection and timed interlocks.
- Interface timing between asynchronous circuits.
Package Contents:
- 1x 74LS221 74221 IC-Dual Non-Retriggerable-Monostable Multivibrator With Reset
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