Texas Instruments SN74AHCT139DR

Overview

SN74AHCT139DR from Texas Instruments is a dual 2-line-to-4-line decoder/demultiplexer in SOIC-16 package, operating at 4.5–5.5 V, with propagation delays as low as 1 ns (t_PLH/t_PHL at 15 pF), TTL-compatible inputs, and ±8 mA output drive. It serves high-speed memory decoding and data-routing applications where minimal system delay is critical.

For engineers reviewing the SN74AHCT139DR datasheet, SN74AHCT139DR pinout, SN74AHCT139DR application, or SN74AHCT139DR equivalent, key selection considerations include its dual-decoder architecture with independent active-low enables, 16-pin SOIC tape-and-reel packaging, guaranteed operation from –40°C to +85°C, and compatibility with legacy TTL logic levels while delivering CMOS power efficiency.

Technical Context

The SN74AHCT139DR implements two independent 2-to-4 decoders, each with separate active-low enable (1G/2G) and binary select inputs (A/B), producing four active-low outputs (Y0–Y3). Its fully buffered inputs present only one normalized load, minimizing loading on upstream drivers.

It uses standard positive-logic decoding with active-low outputs and supports demultiplexing via the enable input acting as a data line. All switching characteristics are specified at V_CC = 5 V ± 0.5 V and CL = 15 pF or 50 pF, with no internal latches or clocks - purely combinational logic behavior.

Key Specifications

Pinout & Package

SN74AHCT139DR is housed in a 16-pin SOIC (D) package, 7.5 mm × 10.3 mm body, 1.75 mm height, with 1.27 mm pitch. Pin 1 is marked by a beveled corner or dot; device orientation follows JEDEC MO-150 standard.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HCT139DR and 74LV139DR, the SN74AHCT139DR delivers the optimal balance of TTL compatibility, sub-10 ns propagation delay at 5 V, and industrial temperature support - making it the preferred choice for upgrading 74LS139 in existing 5 V memory and control systems.

Availability

SN74AHCT139DR is available at Aetrix Electronics and suitable for industrial control panels, legacy system upgrades, and 5 V microcontroller peripheral expansion requiring stable component supply and long-term manufacturability.

Supply support for SN74AHCT139DR 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 founded in 1930, specializing in analog, embedded processing, and logic solutions with broad industrial, automotive, and communications reach.

The SN74AHCT139DR belongs to TI's advanced high-speed CMOS (AHCT) logic family, engineered specifically for seamless 5 V TTL-to-CMOS bridging in memory decoding, data routing, and system control applications where speed, compatibility, and reliability are essential.

FAQ

What is the maximum operating frequency supported by SN74AHCT139DR?

The SN74AHCT139DR is a combinational logic device with no internal clock, so it does not have a rated maximum operating frequency. Its usable toggle rate depends on propagation delay and load capacitance: with CL = 15 pF, t_PD ≤ 8.5 ns supports reliable operation up to ~60 MHz in worst-case cascaded paths. For clean 1-of-4 selection in memory systems, it performs reliably at full bus speeds up to 100 MHz due to tight timing margins. The SN74AHCT139DR datasheet specifies switching characteristics only - no AC limits beyond those derived from t_PD and setup/hold timing.

Can SN74AHCT139DR operate at 3.3 V supply voltage?

No, the SN74AHCT139DR is not rated for 3.3 V operation. Its recommended V_CC range is strictly 4.5 V to 5.5 V per the SCLS267M datasheet. At 3.3 V, input thresholds (VIH ≥ 2 V, VIL ≤ 0.8 V) may still be met, but output drive strength, propagation delay, and noise margins are not guaranteed. For 3.3 V systems, TI recommends SN74LVC139A or SN74LV139 - both pin-compatible alternatives with validated 3.3 V performance. Using SN74AHCT139DR outside its specified V_CC range risks functional failure or reduced reliability.

Is SN74AHCT139DR pin-compatible with the older 74LS139?

Yes, SN74AHCT139DR is a direct pin-compatible and functionally equivalent replacement for 74LS139 in SOIC-16 package. Both share identical pin assignments (1G, 1A, 1B, 1Y0–1Y3, GND, V_CC, 2Y0–2Y3, 2B, 2A, 2G), same active-low enable and output logic, and TTL-compatible input thresholds. The SN74AHCT139DR improves on 74LS139 with lower power consumption, higher noise immunity, and better drive capability - enabling drop-in replacement without PCB or schematic changes in legacy 5 V systems.

What is the meaning of "DR" suffix in SN74AHCT139DR?

The "DR" suffix in SN74AHCT139DR indicates a 16-pin SOIC (D) package supplied in tape-and-reel format with a quantity of 2500 units per reel. This is distinct from "D" (same package, tube packaging) and "DBR" (SSOP-16, tape-and-reel). The DR variant is optimized for automated SMT assembly lines, with standardized reel dimensions (330 mm diameter, 16.4 mm width) and Q1 pin-1 orientation per JEDEC standards. All DR-marked units carry top-side marking "AHCT139" and comply with RoHS and Level-1 MSL reflow requirements.

Does SN74AHCT139DR require pull-up or pull-down resistors on unused inputs?

Yes, all unused inputs of SN74AHCT139DR must be held at a valid logic level - either V_CC or GND - to prevent floating nodes that could cause excessive ICC, erratic outputs, or increased EMI. TI's SCBA004 application report explicitly mandates this for CMOS devices. Leaving inputs unconnected violates recommended operating conditions and may lead to unpredictable behavior, especially under temperature variation or noise. For unused decoder sections, tie 1G/2G high (via 10 kΩ to V_CC) and A/B inputs to GND or V_CC as appropriate; never leave them open. This requirement applies equally to SN74AHCT139DR and all AHCT-family devices.