Texas Instruments SN74HC139DT

Overview

SN74HC139DT from Texas Instruments is a dual 2-line-to-4-line decoder/demultiplexer in SOIC-16 package, operating from 2 V to 6 V with typical propagation delay of 10 ns at 5 V and ±4-mA output drive capability. It features two independent decoders, each with active-low enable (G) and fully buffered inputs, used for memory address decoding and data routing in high-speed digital systems.

For engineers reviewing the SN74HC139DT datasheet, SN74HC139DT pinout, SN74HC139DT application, or SN74HC139DT equivalent, this page delivers verified functional modes, real-world timing behavior, confirmed package dimensions, and validated alternative options for industrial control, instrumentation, and legacy system upgrades.

Technical Context

The SN74HC139DT implements two independent CMOS decoders, each accepting two binary inputs (A, B) and one active-low enable (G), producing four active-low outputs (Y0–Y3). All inputs are fully buffered, presenting only one normalized LSTTL load to driving circuitry.

When G is high, all outputs are forced high regardless of A/B states; when G is low, exactly one output goes low per input combination (00→Y0, 01→Y1, 10→Y2, 11→Y3). This enables cascading via enable chaining and supports demultiplexing by using G as a data input.

Key Specifications

Pinout & Package

SN74HC139DT is housed in a 16-pin SOIC (D) package measuring 9.90 mm × 3.90 mm with 1.27-mm lead pitch and 2.00-mm maximum height. Pin 1 is located at the top-left corner adjacent to the index notch.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC139DT, SN74HC139DR offers identical performance with assured availability, while 74LV139PW trades wider voltage compatibility for speed and lower-voltage optimization-neither is pin-compatible with SN74HC139DT in mixed-supply systems.

Availability

SN74HC139DT is available at Aetrix Electronics and suitable for memory decoding, industrial I/O expansion, and legacy system repair requiring stable component supply despite its obsolete status.

Supply support for SN74HC139DT 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 specializing in analog, embedded processing, and logic ICs, with over 50 years of innovation in high-reliability digital logic families.

The SN74HC139 series was designed for high-speed memory decoding and data-routing applications where minimal propagation delay and low power are critical in commercial and industrial systems.

FAQ

What is the function of the G pin on the SN74HC139DT?

The G pin on the SN74HC139DT is an active-low enable input for each decoder section. When G is high, all four corresponding Y outputs are forced high regardless of A/B inputs. When G is low, the decoder operates normally, asserting exactly one low output per A/B combination. This allows cascading or demultiplexing functionality, and the SN74HC139DT uses separate G pins (pin 3 for Channel 1, pin 12 for Channel 2) to independently control each decoder.

Is SN74HC139DT pin-compatible with older 74LS139 devices?

Yes, SN74HC139DT is pin-compatible with 74LS139 in SOIC-16 packaging, sharing identical pin assignments for inputs (A, B, G), outputs (Y0–Y3), VCC, and GND. However, SN74HC139DT operates with CMOS-level thresholds and draws significantly less current, so it can directly replace 74LS139 in most 5-V systems without redesign-though timing margins improve due to its 10-ns typical tpd versus 25-ns for LS.

What is the maximum clock frequency supported by SN74HC139DT in decoding applications?

SN74HC139DT does not operate on a clock; it is a combinational logic device. Its usable switching rate is determined by propagation delay and system setup/hold timing. With 10-ns typical tpd and 38-ns max transition time (tt), the SN74HC139DT supports reliable operation in address decode paths up to ~25 MHz in worst-case scenarios, and higher in well-bypassed, low-capacitance layouts-making it suitable for 8-bit and 16-bit microcontroller memory maps.

Can SN74HC139DT drive LEDs directly?

SN74HC139DT outputs are active-low and rated for ±4 mA at 5 V, which is sufficient to drive small indicator LEDs with appropriate current-limiting resistors (e.g., 1 kΩ for ~4 mA at 5 V). However, it is not intended for high-current loads: continuous output current must remain within ±25 mA per pin, and total device current must stay below ±50 mA. For LED arrays or higher brightness, external drivers are recommended.

Why is SN74HC139DT marked as obsolete, and what should designers use instead?

SN74HC139DT is obsolete per Texas Instruments' packaging roadmap, with active production shifted to tape-and-reel variants like SN74HC139DR (SOIC) and SN74HC139DBR (SSOP). The silicon and functionality are identical-only packaging and ordering formats differ. Designers should migrate to SN74HC139DR for new designs to ensure long-term supply, while SN74HC139DT remains available for legacy repair through authorized distributors with verified traceable stock.