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Texas Instruments SN74ALS138AN — Discrete Semiconductors

SN74ALS138AN Decoder/Demultiplexer, 1x3:8, 16-DIP, 4.5V-5.5V

MPNSN74ALS138AN
End of Life

Texas Instruments SN74ALS138AN, 74ALS series, Decoder/Demultiplexer, 1 x 3:8, 4.5V ~ 5.5V supply, 16-DIP (0.300", 7.62mm), Through Hole, 0°C ~ 70°C.

$1.13Ref. price · indicative, final on quote
Texas Instruments SN74ALS138AN datasheet (PDF)
Packaging16-DIP (0.300", 7.62mm)
RoHSROHS3 Compliant
Series74ALS
Independent supplier — new & surplus stockAuthenticity-screened · ESD-safe packingListing updated Aug 2026

Specifications

SN74ALS138AN specifications
ParameterValue
TypeDecoder/Demultiplexer
Series74ALS
MountingThrough Hole
Supply voltage4.5V ~ 5.5V
Voltage supply sourceSingle Supply
Current - output high, low400µA, 8mA
Operating temperature0°C ~ 70°C
Circuit1 x 3:8
PackageTube
Case16-DIP (0.300\", 7.62mm)
Independent circuits1

Product details

1-of-8 decoder/demux in a 16-pin DIP

The Texas Instruments SN74ALS138AN is a single 3-line to 8-line decoder/demultiplexer from the 74ALS family. It takes a 3-bit binary input and asserts one of eight active-low outputs — the standard address-decoding or data-routing block for 5V logic boards. The 16-pin DIP (0.300-inch wide, 7.62 mm pitch) is through-hole only, so it fits legacy sockets, protoboards, and point-to-point wiring but not modern SMT reflow. Output drive is asymmetric: 400 µA sourcing, 8 mA sinking. Not rated for industrial enclosures, engine bays, or outdoor telecom cabinets without additional screening or conformal coating.

TI lists the SN74ALS138AN as Active.

What the output drive means for your board

The 400 µA high-level output current and 8 mA low-level output current are typical for ALS logic — the high side is weak. If you're decoding addresses for a memory chip or selecting a peripheral, the load is almost always CMOS or TTL inputs, so the sink current is what matters. If you need to drive a relay coil, LED, or long trace, add a buffer or transistor stage. The 8 mA sink is enough for one or two standard LS/ALS inputs but not for a fan-out of ten.

Frequently asked questions

What is the SN74ALS138AN equivalent or replacement?

There is no official direct replacement listed. The 74LS138 is a functionally similar 3:8 decoder but uses LS logic (lower speed, different drive characteristics). For a pin-compatible ALS upgrade, the SN74ALS138AN itself is the current active part. If you need a surface-mount variant, look at the SN74ALS138AD (SOIC-16) — same die, different package.

SN74ALS138AN vs 74LS138 — what's the difference?

Both are 3:8 decoders in the same pinout and package. The ALS version (SN74ALS138AN) is faster (typical propagation delay around 10 ns vs 20 ns for LS) and draws less supply current per gate. The LS version has slightly higher output drive on the high side (typically 2.7 mA vs 400 µA). For most address-decoding tasks, the ALS is the better choice if the rest of the board is ALS or AS logic.