74LS139 Dual 2-to-4 line decoder, active-low
The 74LS139 holds two independent 2-to-4 line decoders. In each half, the select inputs B A choose one of four active-low outputs, which goes low while the others stay high. Each half has its own active-low enable G′; with G′ high, all four outputs stay high.
74LS139 pinout
Top view of the 16-pin DIP package. Pin 1 is at the bottom left, beside the notch, and the numbers run anticlockwise. Power is on pin 16 (VCC, +5 V) and pin 8 (GND).
| Pin | Name | Type | What it is |
|---|---|---|---|
| 1 | 1G′ | Input | Input, active-low |
| 2 | 1A | Input | Input |
| 3 | 1B | Input | Input |
| 4 | 1Y0′ | Output | Totem-pole output, active-low |
| 5 | 1Y1′ | Output | Totem-pole output, active-low |
| 6 | 1Y2′ | Output | Totem-pole output, active-low |
| 7 | 1Y3′ | Output | Totem-pole output, active-low |
| 8 | GND | Ground | 0 V |
| 9 | 2Y3′ | Output | Totem-pole output, active-low |
| 10 | 2Y2′ | Output | Totem-pole output, active-low |
| 11 | 2Y1′ | Output | Totem-pole output, active-low |
| 12 | 2Y0′ | Output | Totem-pole output, active-low |
| 13 | 2B | Input | Input |
| 14 | 2A | Input | Input |
| 15 | 2G′ | Input | Input, active-low |
| 16 | VCC | Power | +5 V supply |
74LS139 truth table
| B | A | Y0′ | Y1′ | Y2′ | Y3′ |
|---|---|---|---|---|---|
| 0 | 0 | 0 | 1 | 1 | 1 |
| 0 | 1 | 1 | 0 | 1 | 1 |
| 1 | 0 | 1 | 1 | 0 | 1 |
| 1 | 1 | 1 | 1 | 1 | 0 |
What the 74LS139 is used for
- Decoding two address lines into four chip selects
- Implementing two-variable functions from minterms
- A 1-to-4 demultiplexer, using the enable as the data input
Electrical summary
| Package | 16-pin DIP |
| Supply voltage | 5 V (4.75 V to 5.25 V) |
| Supply current, typical | 6.8 mA |
| Output type | Totem-pole — drives both high and low |
| Output current, low | sinks up to 8 mA |
| Output current, high | sources up to 0.4 mA |
| Input current, low | 0.4 mA out of each input held low |
| Fan-out | one output can drive about 20 LS inputs |
Typical figures for quick reference when planning a board. Check the manufacturer's datasheet for limits and timing before committing a design. The 74HC139 and 74HCT139 use the same pin numbers, with different electrical values.
Try the 74LS139 on a breadboard
The Breadboard Simulator has the 74LS139 in its parts library: seat it on a virtual breadboard, wire it, power the board and probe the pins before you build the real thing.