Texas Instruments SN74HC139PWT

Overview

SN74HC139PWT from Texas Instruments is a dual 2-line-to-4-line decoder/demultiplexer in a 16-pin TSSOP package, operating across 2 V to 6 V. It delivers 10 ns typical propagation delay, ±4 mA output drive at 5 V, and supports high-speed memory decoding and data routing with two independent active-low enable inputs (G1, G2) for cascading or demultiplexing control.

For engineers reviewing the SN74HC139PWT datasheet, SN74HC139PWT pinout, SN74HC139PWT application, or SN74HC139PWT equivalent, this device is selected for low-power, high-speed logic decoding where precise output enable timing, LSTTL-load compatibility, and dual-channel independence are critical in memory subsystems and address selection circuits.

Technical Context

The SN74HC139PWT implements two fully buffered, independent 2-to-4 decoders sharing no internal signal paths - each with dedicated A/B select inputs and active-low G strobe. Its CMOS architecture ensures rail-to-rail output swing and input thresholds referenced to VCC, enabling interoperability across mixed-voltage logic families.

Each decoder operates in two functional modes: when its G input is high, all four outputs (Y0–Y3) are forced high; when G is low, exactly one output goes low per binary A/B combination (00→Y0, 01→Y1, etc.), with all others remaining high. No internal pull-ups or latching is present - outputs reflect real-time input states.

Key Specifications

Pinout & Package

TSSOP-16 (PW) package: 5.00 mm × 4.40 mm body, 0.65 mm pitch, 1.2 mm max height, RoHS-compliant NiPdAu lead finish, MSL Level-1 (260 °C peak reflow).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC139PWT, SN74HCT139PWR improves input compatibility with legacy TTL but sacrifices some noise margin at 3.3 V; 74AC139MTCX delivers 35% lower propagation delay and 10× higher drive capability, at the cost of 5× higher quiescent current - ideal for speed-critical, well-bypassed designs.

Availability

SN74HC139PWT is available at Aetrix Electronics and suitable for industrial control panels, memory expansion modules, and embedded peripheral multiplexing requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for SN74HC139PWT 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 high-reliability logic ICs.

The SN74HC139PWT belongs to TI's 74HC logic family - designed for low-power, high-noise-immunity digital control in industrial, computing, and communications equipment where predictable timing and wide VCC tolerance are essential.

FAQ

What is the maximum clock frequency supported by SN74HC139PWT in decoder mode?

The SN74HC139PWT does not operate on a clock - it is combinational logic. Its usable input transition rate is limited by propagation delay and input transition time specs: at VCC = 4.5 V, Δt/Δv ≤ 500 ns ensures reliable operation. For repetitive address changes, the effective maximum toggle rate is ~10 MHz assuming 10 ns tpd and setup/hold margins - verified in TI's SCLS108E switching characteristics table.

Can SN74HC139PWT drive LEDs directly without current-limiting resistors?

No. While SN74HC139PWT provides ±4 mA output drive at 5 V, its absolute maximum continuous output current is ±25 mA per pin - but sustained DC current causes excessive junction heating and violates recommended operating conditions. Always use series resistors (e.g., 330 Ω for 5 V, 20 mA LED) to limit current and ensure reliability per TI's Absolute Maximum Ratings table.

Is SN74HC139PWT pin-compatible with SN74HC138?

No. SN74HC139PWT is a dual 2-to-4 decoder in 16-pin TSSOP; SN74HC138 is a single 3-to-8 decoder in 16-pin packages (SOIC, TSSOP). Pin functions, truth tables, and enable structures differ fundamentally - G1/G2 on SN74HC139PWT vs. E1/E2/E3 on SN74HC138 - making them functionally and physically incompatible replacements.

Does SN74HC139PWT require external pull-up resistors on its outputs?

No. SN74HC139PWT features totem-pole CMOS outputs capable of actively driving both high and low states. Pull-ups are unnecessary and would increase power consumption and slow low-to-high transitions. Outputs are specified to drive 10 LSTTL loads directly - confirmed in TI's "Outputs can drive up to 10 LSTTL loads" feature list and Electrical Characteristics table.

What is the thermal resistance (RθJA) of SN74HC139PWT in its TSSOP-16 package?

The junction-to-ambient thermal resistance RθJA for SN74HC139PWT (TSSOP-16, PW package) is 108 °C/W, as documented in TI's SCLS108E Thermal Information table. This value assumes standard JEDEC 2-layer board layout; actual thermal performance improves with copper pour and thermal vias under the exposed pad (if present) - though the PW package has no exposed thermal pad.