Texas Instruments CD74AC139M

Overview

CD74AC139M from Texas Instruments is a dual 2-line-to-4-line decoder/demultiplexer in SOIC-16 package, operating from 1.5 V to 5.5 V, with ±24-mA output drive, balanced propagation delays (2.6–10.5 ns at VCC = 5 V), and SCR-latchup-resistant CMOS process. It serves in high-speed memory decoding and data routing where low system delay and noise immunity are critical.

For engineers reviewing the CD74AC139M datasheet, CD74AC139M pinout, CD74AC139M application, or CD74AC139M equivalent, key selection considerations include its dual-decoder architecture with active-low enable inputs, 16-pin SOIC thermal performance (θJA = 73°C/W), and operation across –55°C to 125°C industrial/military temperature range.

Technical Context

The CD74AC139M implements two independent 2-to-4 decoders, each with fully buffered inputs and an active-low enable (G) input usable as a data line in demultiplexing mode. Each decoder accepts two select inputs (A, B) and drives four active-low outputs (Y0–Y3).

Its logic function follows standard binary decoding: when G = L, outputs Y0–Y3 reflect the inverse of the 2-bit input combination (e.g., A=0,B=0 → Y0=L, others=H); when G = H, all outputs remain high. Propagation delays are matched between A/B and G inputs to any Y output, enabling predictable timing in cascaded or synchronous routing applications.

Key Specifications

Pinout & Package

CD74AC139M is housed in a 16-pin SOIC (D) package with standard 1.27-mm pitch and JEDEC MO-012AC outline. Thermal resistance θJA = 73°C/W supports reliable operation in compact, convection-cooled layouts.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar dual 2-to-4 decoder applications.

Compared with CD74AC139M, SN74AC139DR offers identical performance with enhanced supply chain support, while CD74HC139M trades speed and drive for lower static power and wider voltage tolerance-making it viable only in non-critical, low-frequency implementations.

Availability

CD74AC139M is available at Aetrix Electronics and suitable for high-reliability memory decoding, industrial bus demultiplexing, and legacy system restoration requiring stable component supply across extended temperature ranges.

Supply support for CD74AC139M 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 leader delivering analog, embedded processing, and logic solutions with emphasis on reliability, longevity, and industrial-grade qualification.

The CD74AC139M belongs to TI's AC-series advanced CMOS logic family, designed specifically for high-speed, low-power, noise-immune digital interfacing in aerospace, defense, and harsh-environment industrial systems.

FAQ

What is the maximum operating frequency supported by the CD74AC139M?

The CD74AC139M does not specify a maximum clock frequency in its datasheet because it is a combinational logic device-not clocked. Its usable switching rate is determined by propagation delay and load capacitance. At VCC = 5 V and CL = 50 pF, tPHL/tPLH ≤ 10.5 ns, supporting reliable operation up to approximately 50 MHz in worst-case routing scenarios. For CD74AC139M-based address decoders, system timing is governed by memory access time minus this delay.

Is the CD74AC139M pin-compatible with the older 74LS139?

No, the CD74AC139M is not pin-compatible with the 74LS139. While both are dual 2-to-4 decoders, the 74LS139 uses a different pin assignment: its G inputs are on pins 1 and 15, whereas CD74AC139M places 1G on pin 1 and 2G on pin 15 but assigns Y outputs differently (e.g., 1Y0 on pin 4 vs. 74LS139's pin 3). Direct substitution requires PCB redesign. CD74AC139M replaces CD74AC139E (PDIP) and CD74HC139M (same SOIC pinout) instead.

Can the CD74AC139M operate from a 1.8-V supply in low-power applications?

Yes, the CD74AC139M is fully specified to operate from 1.5 V to 5.5 V, including 1.8 V. At VCC = 1.8 V, VIH = 1.26 V and VIL = 0.54 V (30% noise margin), and propagation delay increases to 119 ns (CL = 50 pF), making it suitable for ultra-low-power, low-speed control logic where timing budgets allow. All DC parameters-including ±24-mA drive-are guaranteed across the full VCC range, so CD74AC139M maintains functional integrity at 1.8 V.

Does the CD74AC139M require external pull-up resistors on its outputs?

No, the CD74AC139M features totem-pole (push-pull) outputs-not open-drain-so external pull-ups are not required. Its Y outputs actively drive both high and low states, with VOH ≥ 4.4 V and VOL ≤ 0.1 V at VCC = 4.5 V and IOL = 24 mA. Pull-ups would conflict with active-high drive and risk excessive current; they are only needed if intentionally configuring wired-OR logic using external diodes or if interfacing with legacy NMOS loads requiring stronger high-side sourcing.

What is the thermal performance difference between CD74AC139M and CD74AC139E packages?

The CD74AC139M (SOIC-16) has a junction-to-ambient thermal resistance θJA of 73°C/W, while the CD74AC139E (PDIP-16) is rated at 67°C/W. This 6°C/W difference means the SOIC package runs ~6°C hotter under identical power dissipation and board conditions. However, the SOIC's smaller footprint and better solder-joint reliability make it preferable for high-density layouts-provided ambient temperature and airflow are managed. Both packages share the same –55°C to 125°C operating range, and CD74AC139M's lower mass enables faster thermal response during transient loads.