Texas Instruments CD54HC138F3A

Overview

CD54HC138F3A from Texas Instruments is a high-speed CMOS 3-to-8 line decoder/demultiplexer with active-low outputs, operating across 2 V to 6 V supply range, featuring 13 ns typical propagation delay at 5 V/15 pF, -55°C to +125°C temperature rating, and three enable inputs (G2, G1, G0) for cascading in memory address decoding applications.

For engineers reviewing the CD54HC138F3A datasheet, CD54HC138F3A pinout, CD54HC138F3A application, or CD54HC138F3A equivalent, this device serves as a precision logic-level selector in aerospace-grade digital systems requiring wide-temperature reliability, low-power CMOS compatibility, and deterministic output enable control.

Technical Context

The CD54HC138F3A implements a silicon-gate CMOS 3:8 decoder with three address inputs (A2–A0) and three independent strobe enables (G2, G1, G0), where any active-low strobe forces all eight outputs (Y0–Y7) high. Its function table defines 8 decoded states only when all strobes are asserted (G2 = H, G1 = L, G0 = L).

It uses standard CMOS input thresholds (VIH = 3.15 V min, VIL = 1.35 V max at VCC = 4.5 V), delivers ±4 mA output drive capability, and exhibits balanced rise/fall times (tt ≤ 19 ns at 4.5 V/15 pF), making it suitable for synchronous bus selection and address demultiplexing in radiation-tolerant embedded controllers.

Key Specifications

Pinout & Package

CD54HC138F3A is housed in a 16-pin Ceramic Dual In-line Package (CDIP-J) with 21.34 mm × 6.92 mm body size, hermetically sealed for high-reliability applications and compatible with through-hole soldering processes.

Key Features

Applications

Equivalent & Alternatives

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

Compared with CD74HC138E, the CD54HC138F3A delivers guaranteed military-temperature operation and hermetic reliability, while CD54HCT138F3A trades CMOS input noise margin for direct TTL logic compatibility-neither is pin-compatible with non-CDIP variants.

Availability

CD54HC138F3A is available at Aetrix Electronics and suitable for aerospace vehicle control units, secure military data acquisition systems, rad-hard telemetry hubs, and tactical RF front-end controllers requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for CD54HC138F3A 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 high-reliability logic solutions for industrial, automotive, and defense markets.

The CD54HC138F3A belongs to TI's military-grade HC logic family, designed specifically for high-integrity digital control in mission-critical systems where temperature resilience, long-term parametric stability, and process traceability are mandatory.

FAQ

What is the maximum clock/data rate supported by CD54HC138F3A in demultiplexer mode?

The CD54HC138F3A does not operate as a clocked device but functions combinatorially. Its maximum usable data rate in demux mode is determined by propagation delay (13 ns typ) and output transition time (≤19 ns). For reliable operation, input address and strobe edges must settle ≥30 ns before output stabilization-supporting effective demux rates up to ~15 MHz in controlled impedance environments.

Does CD54HC138F3A require external pull-up resistors on its outputs?

No, CD54HC138F3A features totem-pole CMOS outputs-not open-drain-so external pull-ups are unnecessary. Each output (Y0–Y7) actively drives both high and low states. Pull-ups would cause contention and excessive current draw when outputs switch low; proper operation assumes direct connection to CMOS or TTL inputs with appropriate load capacitance (≤50 pF).

Can CD54HC138F3A be operated at 3.3 V supply voltage?

Yes, CD54HC138F3A is fully specified for 2 V to 6 V operation. At 3.3 V, VIH = 2.31 V min and VIL = 0.99 V max ensure compatibility with 3.3 V LVTTL and LVCMOS logic families. Propagation delay increases to ~22 ns (typ), and output drive reduces to ±3 mA, remaining sufficient for driving 10 LSTTL loads or modern low-capacitance interfaces.

How does the enable logic of CD54HC138F3A differ from standard '138 decoders?

The CD54HC138F3A uses identical enable architecture to industry-standard 74HC138: G2 is active-high, G1 and G0 are active-low. All three must be simultaneously asserted (G2 = H, G1 = L, G0 = L) for decoding. This triple-enable scheme allows daisy-chaining multiple CD54HC138F3A devices using one unit's outputs to control another's G2/G1/G0, enabling 1-of-64 or larger decoding trees without additional gates.

Is CD54HC138F3A compliant with RoHS or lead-free assembly requirements?

No, CD54HC138F3A uses SnPb (tin-lead) lead finish per MIL-PRF-38535 Class B requirements and is explicitly marked "No" for RoHS compliance in TI's packaging addendum. It is intended for high-reliability applications where solder joint integrity under thermal cycling outweighs environmental directives; alternative RoHS-compliant options like CD74HC138M96 require derating for military temperature use.