# SN74LS221DBR

**Texas Instruments** · Monostable Multivibrators · SSOP-16-208mil

SN74LS221DBR from Texas Instruments, in a SSOP-16-208mil. Pinout and pin descriptions extracted from the manufacturer datasheet (extract_pins, cross-checked by a second model); symbol, footprint, and 3D from KiCad-official CAD.

## Pinout

| Pin | Name | Type | Function |
|---|---|---|---|
| 1 | 1A | input | Monostable 1 negative-transition-triggered input, which can also be used as an inhibit input; unused inputs must be held at VCC or GND. |
| 2 | 1B | input | Monostable 1 positive-transition-triggered Schmitt-trigger input, which can also be used as an inhibit input. |
| 3 | 1CLR | input | Monostable 1 active-low overriding clear input that terminates the output pulse. |
| 4 | 1Q̄ | output | Monostable 1 complementary (inverted) totem-pole output, high when idle; IOL 8 mA max and IOH -400 µA for the SN74LS221. |
| 5 | 2Q | output | Monostable 2 totem-pole output, low when idle and high during the pulse; IOL 8 mA max and IOH -400 µA for the SN74LS221. |
| 6 | 2Cext | passive | Monostable 2 external timing capacitor connection; the Rext/Cext terminal is never more positive than this terminal. |
| 7 | 2Rext/Cext | passive | Monostable 2 external timing resistor/capacitor junction; Rext 1.4 kΩ min to 100 kΩ max for the SN74LS221, with tw ≈ 0.7·Cext·Rext. |
| 8 | GND | power_in | Ground. |
| 9 | 2A | input | Monostable 2 negative-transition-triggered input, which can also be used as an inhibit input. |
| 10 | 2B | input | Monostable 2 positive-transition-triggered Schmitt-trigger input, which can also be used as an inhibit input. |
| 11 | 2CLR | input | Monostable 2 active-low overriding clear input that terminates the output pulse. |
| 12 | 2Q̄ | output | Monostable 2 complementary (inverted) totem-pole output, high when idle; IOL 8 mA max and IOH -400 µA for the SN74LS221. |
| 13 | 1Q | output | Monostable 1 totem-pole output, low when idle and high during the pulse; IOL 8 mA max and IOH -400 µA for the SN74LS221. |
| 14 | 1Cext | passive | Monostable 1 external timing capacitor connection; the Rext/Cext terminal is never more positive than this terminal. |
| 15 | 1Rext/Cext | passive | Monostable 1 external timing resistor/capacitor junction; Rext 1.4 kΩ min to 100 kΩ max for the SN74LS221, with tw ≈ 0.7·Cext·Rext. |
| 16 | VCC | power_in | Supply voltage, 4.75 V to 5.25 V recommended for the SN74LS221 (7 V absolute maximum). |

## Key specifications

| Parameter | Value |
|---|---|
| Manufacturer | Texas Instruments |
| Package | SSOP-16-208mil |
| Category | Logic ICs |
| Pins | 16 |

## CAD (KiCad official)

- Symbol: `SN74LS221DBR`
- Footprint: `Package_SO:SSOP-16_5.3x6.2mm_P0.65mm`
- 3D model: SSOP-16-208mil (KiCad packages3D, STEP)
- 3D model files: `sn74ls221dbr-etched.step` / `sn74ls221dbr-etched.glb` carry the MPN laser-etched on the die in a toggleable `Adom.LaserEtch` group (Fusion-ready); `sn74ls221dbr.step` / `sn74ls221dbr.glb` are the bare package body.

## Provenance

Data extracted from the manufacturer datasheet, not a distributor listing:

- **Datasheet:** [Texas Instruments datasheet](https://www.ti.com/cn/lit/gpn/sn74ls221) (31 pp, sha256 `9d7f372b30430c70`, retrieved 2026-10-08, tier: lcsc)
- **Extractor:** parts-factory `2.0.0` / `extract_pins 0.3`, primary `claude-sonnet-5-5` (text+vision), consensus `claude-opus-5-5` (agreed), guards: pin_guards 0.1: passed. Pins are checked against the footprint pad set and their cited datasheet pages before publish.
- **CAD:** KiCad official libraries (CC-BY-SA 4.0).

[Datasheet PDF](docs/sn74ls221dbr-datasheet.pdf)