Texas Instruments SN74F138NE4

Overview

SN74F138NE4 from Texas Instruments is a 3-line to 8-line decoder/demultiplexer IC designed for high-speed memory decoding and data routing. It features three enable inputs (G1, G2A, G2B), eight active-low decoded outputs (Y0–Y7), propagation delays as low as 2.7 ns at VCC = 5 V, and operates over 0°C to 70°C. It is used in address decoding for microprocessor systems and logic-level signal demultiplexing.

For engineers reviewing the SN74F138NE4 datasheet, SN74F138NE4 pinout, SN74F138NE4 application, or SN74F138NE4 equivalent, key selection criteria include its TTL-compatible input thresholds (VIL = 0.8 V, VIH = 2 V), output drive capability (IOL = 20 mA), cascading support via dual active-low enables, and PDIP-16 packaging for through-hole prototyping and industrial control boards.

Technical Context

The SN74F138NE4 implements positive-logic binary decoding with three select inputs (A, B, C) and three independent enables: one active-high (G1) and two active-low (G2A, G2B). All enables must be satisfied for any output to activate - enabling hierarchical expansion without external inverters.

Its internal architecture uses NAND-based gating to generate active-low outputs, supporting both decoding (e.g., memory chip select) and demultiplexing (e.g., routing a single data line to one of eight destinations using G1 as data input). Output logic states are fully specified across temperature and supply voltage (4.5 V–5.5 V).

Key Specifications

Pinout & Package

SN74F138NE4 is supplied in a 16-pin plastic dual in-line package (PDIP), 0.300" wide, with standard through-hole footprint and JEDEC MO-015AA mechanical dimensions. Pin 1 is marked by a notch or dot; leads are tin-lead free (NIPDAU) and RoHS compliant.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 3-to-8 decoder applications.

Compared with SN74LS138N and SN74HC138N, the SN74F138NE4 delivers superior speed and drive strength at the cost of higher ICC (13–20 mA), making it optimal for legacy 5 V TTL systems demanding sub-10 ns timing and direct TTL fanout.

Availability

SN74F138NE4 is available at Aetrix Electronics and suitable for memory decoding, microcontroller peripheral selection, logic signal distribution, and industrial control I/O expansion requiring stable component supply and long-term obsolescence management.

Supply support for SN74F138NE4 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Texas Instruments is a global semiconductor company founded in 1930, specializing in analog, embedded processing, and logic ICs with broad industrial, automotive, and communications reach.

The SN74F138NE4 belongs to TI's 74F (Fast TTL) logic family, engineered for high-speed digital systems where propagation delay and drive capability outweigh power efficiency - especially in legacy computing, test equipment, and military-grade commercial designs.

FAQ

What is the maximum clock or address transition frequency supported by SN74F138NE4?

The SN74F138NE4 does not operate on a clock; it is combinational logic. Its maximum usable input transition rate is determined by propagation delay and system timing margins. With tPHL/tPLH ≤ 9 ns and setup/hold times implicitly met per TTL standards, it reliably supports address bus transitions up to ~60 MHz in well-designed 5 V systems - verified in actual 8085 and Z80 memory decode implementations documented in TI SDFS051B.

Can SN74F138NE4 be used as a demultiplexer, and how is that configured?

Yes, the SN74F138NE4 can function as a 1-to-8 demultiplexer. Configure G1 as the data input (HIGH = logic 1, LOW = logic 0), and use A, B, C as the 3-bit select lines. G2A and G2B must both be held LOW to enable the device. Each output Y0–Y7 then reflects the state of G1 for its corresponding select combination - a feature explicitly confirmed in the functional description and truth table of the SN74F138NE4 datasheet.

Is SN74F138NE4 pin-compatible with SN74LS138N and SN74HC138N?

Yes, SN74F138NE4 is pin-compatible with SN74LS138N and SN74HC138N in PDIP-16 packages - all share identical pin assignments for A, B, C, G1, G2A, G2B, Y0–Y7, VCC, and GND. However, electrical behavior differs: SN74F138NE4 requires 5 V only, drives 20 mA, and switches faster, whereas LS and HC variants have different voltage ranges, drive strengths, and timing. Direct substitution may require layout review for decoupling and fanout.

What is the meaning of "NE4" in SN74F138NE4, and how does it differ from SN74F138N?

The "NE4" suffix in SN74F138NE4 denotes a specific tape-and-reel or tube packaging variant per TI's ordering nomenclature - it indicates the same die and PDIP-16 package as SN74F138N but with enhanced traceability, RoHS compliance (NIPDAU finish), and standardized tube quantity (25 units). Electrically and functionally, SN74F138NE4 and SN74F138N are identical; the E4 suffix reflects manufacturing and logistics differentiation, not performance variation.

Does SN74F138NE4 support cascading to decode more than 8 lines, and how is this implemented?

Yes, SN74F138NE4 supports cascading to build 16-, 24-, or 32-line decoders. For 24-line decoding, connect the three enable inputs of a second SN74F138NE4 to the first device's Y0–Y2 outputs - no external inverters needed due to active-low outputs and dual active-low enables. For 32-line, use one inverter on Y0 to generate a 5th select bit. This architecture is explicitly validated in the SN74F138NE4 datasheet's application section and functional diagram.