Texas Instruments SN74HCT139DBR

Overview

SN74HCT139DBR from Texas Instruments is a dual 2-line-to-4-line decoder/demultiplexer in SSOP-16 package, operating at 4.5–5.5 V, with 10 ns typical propagation delay, ±4-mA output drive, and TTL-compatible inputs. It serves as a high-speed address decoder in memory subsystems and enables data routing in industrial control logic.

For engineers reviewing the SN74HCT139DBR datasheet, SN74HCT139DBR pinout, SN74HCT139DBR application, or SN74HCT139DBR equivalent, key selection criteria include active-low enable architecture, dual independent decoder operation, guaranteed LSTTL load drive (10 loads), low ICC (80 µA max), and SSOP-16 thermal performance (RθJA = 82°C/W).

Technical Context

The SN74HCT139DBR integrates two fully buffered, independent 2-to-4 decoders sharing no internal signal paths-each features separate active-low enable (G) and binary select inputs (A, B), supporting cascaded decoding or parallel demultiplexing. Its HCT logic family ensures TTL-level input thresholds while delivering CMOS-level noise immunity and static power efficiency.

Propagation delay is tightly specified across voltage (4.5 V to 5.5 V) and temperature (−40°C to +85°C), with tpd ≤ 50 ns (max) at 4.5 V and ≤ 40 ns (max) at 5.5 V under 50-pF load. Output drive capability is characterized at both 20 µA (for logic-level integrity) and 4 mA (for fanout), with VOL ≤ 0.33 V and VOH ≥ 3.7 V at full drive.

Key Specifications

Pinout & Package

SN74HCT139DBR uses a 16-pin SSOP (Shrink Small Outline Package) with 0.65-mm lead pitch, 6.2 mm × 5.3 mm body size, and 2.0-mm maximum height. Pin 1 is located in Quadrant Q1 per tape-and-reel orientation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS139DR and SN74HC139PWR, the SN74HCT139DBR uniquely balances TTL input compatibility, 5-V-only robustness, low static power, and sub-12-ns speed-making it optimal for industrial upgrades of 5-V memory and control systems where signal integrity and legacy interoperability are critical.

Availability

SN74HCT139DBR is available at Aetrix Electronics and suitable for industrial control panels, legacy system repairs, and memory subsystem upgrades requiring stable component supply and long-term obsolescence management.

Supply support for SN74HCT139DBR 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 solutions, with over 50 years of innovation in industrial, automotive, and communications markets.

The SN74HCT139DBR belongs to TI's HCT logic family-designed specifically for high-speed memory decoding and data-routing applications where TTL compatibility, low power, and precise timing are essential.

FAQ

What is the maximum propagation delay of the SN74HCT139DBR at 4.5 V?

The maximum propagation delay (tpd) of the SN74HCT139DBR is 51 ns at 4.5 V and 25°C with CL = 50 pF, as specified in the Switching Characteristics table. This value applies to transitions at both A/B and G inputs to any Y output. The SN74HCT139DBR maintains consistent timing across its full operating temperature range (−40°C to +85°C), with worst-case tpd increasing to 51 ns at low VCC and elevated temperature extremes.

Does the SN74HCT139DBR support mixed-voltage operation between 3.3 V and 5 V logic?

No, the SN74HCT139DBR does not support mixed-voltage operation. It requires a 4.5–5.5 V supply and is designed exclusively for 5-V systems. Its inputs are TTL-compatible (VIH = 2 V min, VIL = 0.8 V max), allowing direct connection to 3.3-V CMOS outputs only if those outputs guarantee VOH ≥ 2.4 V and VOL ≤ 0.4 V under load-however, TI does not characterize or guarantee such interfacing. For reliable 3.3-V/5-V translation, a dedicated level shifter or the SN74HC139 should be used instead of the SN74HCT139DBR.

Can unused inputs on the SN74HCT139DBR be left floating?

No, unused inputs on the SN74HCT139DBR must never be left floating. All unused A, B, or G inputs must be tied to either VCC or GND to prevent undefined logic states, increased ICC, or oscillation. TI explicitly recommends connecting unused inputs to VCC or GND per the Recommended Operating Conditions section. Floating inputs may cause excessive current draw or erratic output behavior due to intermediate voltage levels triggering both PMOS and NMOS transistors simultaneously within the input buffer.

What is the thermal resistance (RθJA) of the SN74HCT139DBR in its SSOP-16 package?

The junction-to-ambient thermal resistance (RθJA) of the SN74HCT139DBR in the SSOP-16 (DB) package is 82°C/W, as documented in the Thermal Information table. This value assumes standard JEDEC high-K board conditions (2S2P). Actual thermal performance depends on PCB copper area, airflow, and nearby heat sources; for sustained 80-µA ICC operation, self-heating remains negligible (<0.1°C rise), but under worst-case switching conditions with full output loading, thermal design margin should account for this RθJA value.

Is the SN74HCT139DBR pin-compatible with other package variants of the same part number?

Yes, the SN74HCT139DBR is functionally and pinout-compatible with other SN74HCT139 variants in SOIC (D), PDIP (N), and TSSOP (PW) packages. Pin numbering and signal assignments (G1, A1, B1, Y10–Y13, G2, A2, B2, Y20–Y23, VCC, GND) are identical across all packages, as confirmed in the Pin Configuration and Functions section. However, mechanical dimensions, thermal performance, and reflow profiles differ-SSOP (DB) has tighter pitch (0.65 mm) and lower RθJA (82°C/W) than PDIP (67°C/W) but higher than TSSOP (108°C/W).