SN74HC139 Dual 2-to-4 Decoder

@@ -0,0 +1,64 @@+# SN74HC139++**Texas Instruments** · Decoder / Demultiplexer · SOIC-16++The SN74HC139 contains two independent 2-to-4 line decoders/demultiplexers. Each takes two address inputs and an active-low enable, driving one of four active-low outputs low. It is a common way to generate chip selects or route a signal to one of four destinations.++## Pinout++| Pin | Name | Type | Function |+|---|---|---|---|+| 1 | 1G | input | Decoder 1 active-low enable (strobe). When high, all 1Y0-1Y3 outputs are forced high; when low, the selected output is driven low. Can be used as a data input in demultiplexing applications. |+| 2 | 1A | input | Decoder 1 select input A (LSB of the 2-bit address for decoder 1). |+| 3 | 1B | input | Decoder 1 select input B (MSB of the 2-bit address for decoder 1). |+| 4 | 1Y0 | output | Decoder 1 active-low output 0. Driven low when 1G=L and (1B,1A)=(0,0); otherwise high. IOH = -4 mA / IOL = 4 mA at VCC = 4.5 V. |+| 5 | 1Y1 | output | Decoder 1 active-low output 1. Driven low when 1G=L and (1B,1A)=(0,1); otherwise high. |+| 6 | 1Y2 | output | Decoder 1 active-low output 2. Driven low when 1G=L and (1B,1A)=(1,0); otherwise high. |+| 7 | 1Y3 | output | Decoder 1 active-low output 3. Driven low when 1G=L and (1B,1A)=(1,1); otherwise high. |+| 8 | GND | power_in | Ground reference (0 V) for both decoders. |+| 9 | 2Y3 | output | Decoder 2 active-low output 3. Driven low when 2G=L and (2B,2A)=(1,1); otherwise high. |+| 10 | 2Y2 | output | Decoder 2 active-low output 2. Driven low when 2G=L and (2B,2A)=(1,0); otherwise high. |+| 11 | 2Y1 | output | Decoder 2 active-low output 1. Driven low when 2G=L and (2B,2A)=(0,1); otherwise high. |+| 12 | 2Y0 | output | Decoder 2 active-low output 0. Driven low when 2G=L and (2B,2A)=(0,0); otherwise high. |+| 13 | 2B | input | Decoder 2 select input B (MSB of the 2-bit address for decoder 2). |+| 14 | 2A | input | Decoder 2 select input A (LSB of the 2-bit address for decoder 2). |+| 15 | 2G | input | Decoder 2 active-low enable (strobe). When high, all 2Y0-2Y3 outputs are forced high; when low, the selected output is driven low. Can be used as a data input in demultiplexing applications. |+| 16 | VCC | power_in | Positive supply, 2 V to 6 V (5 V nominal). Bypass with a 0.1 uF capacitor close to the pin (0.1 uF and 1 uF in parallel is common). |++## Key specifications++| Parameter | Value |+|---|---|+| Type | Dual 2-to-4 decoder / demultiplexer |+| Logic family | 74HC (CMOS) |+| Outputs | Active-low, one-of-four per decoder |+| Supply voltage | 2 V to 6 V |+| Propagation delay | 16 ns typ at 5 V |+| Operating temperature | -40 C to 85 C |++## Ordering variants++- `SN74HC139D`+- `SN74HC139DB`+- `SN74HC139N`+- `SN74HC139NS`+- `SN74HC139PW`+- `SN74HC139J`+- `SN74HC139W`+- `SN74HC139FK`++## CAD (KiCad official)++- Symbol: `sn74hc139.kicad_sym`+- Footprint: `sn74hc139.kicad_mod`+- 3D model: SOIC-16 body from KiCad `Package_SO/SOIC-16_3.9x9.9mm_P1.27mm`.++## Provenance++Data extracted from the manufacturer datasheet, not a distributor listing:++- **Datasheet:** [Texas Instruments datasheet](https://www.ti.com/lit/ds/symlink/sn74hc139.pdf) (30 pp, sha256 `7bed90a2f9c2fe80`, retrieved 2026-08-17, tier: manufacturer)+- **Extractor:** `ds2sf` (Claude). Every pin and dimension is cited to a datasheet page; it refuses to fabricate.+- **CAD:** KiCad official libraries (CC-BY-SA 4.0).++[Datasheet PDF](docs/sn74hc139-datasheet.pdf)

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