STMicroelectronics 74LCX139TTR

Overview

74LCX139TTR from STMicroelectronics is a low-voltage CMOS dual 2-to-4 decoder/demultiplexer with 5V-tolerant inputs, 6.2ns max propagation delay at 3V, ±24mA output drive, 2.0–3.6V operating range, and active-low enable inputs-used in 3.3V logic interfacing with legacy 5V systems in telecom backplanes and industrial I/O modules.

For engineers reviewing the 74LCX139TTR datasheet, 74LCX139TTR pinout, 74LCX139TTR application, or 74LCX139TTR equivalent, key selection criteria include input voltage tolerance, symmetric output drive capability, propagation delay matching (tPLH ≅ tPHL), and SO/TSSOP package compatibility with high-density PCB layouts.

Technical Context

The device implements two independent 2-to-4 decoders, each with an active-low enable (G) that gates all four outputs high when asserted. Address inputs (A, B) select one of four active-low outputs per section, supporting both decoding and demultiplexing functions without external inversion.

Its C2MOS fabrication enables rail-to-rail 5V-tolerant inputs while operating from 2.0–3.6V VCC, and built-in power-down protection prevents current flow on inputs/outputs during VCC = 0V-critical for hot-swap and partial-power-down systems.

Key Specifications

Pinout & Package

TSSOP16 package: 5.0mm × 4.4mm body, 0.65mm pitch, lead-free ECOPACK® compliant, 16-pin surface-mount with exposed pad not present.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LVC139APWR and 74AHC139PW, the 74LCX139TTR uniquely combines 5V input tolerance, symmetric ±24mA drive, and sub-7ns delay at 3V - making it optimal for mixed-voltage backplane and adapter designs where interface robustness and timing precision are co-constrained.

Availability

74LCX139TTR is available at Aetrix Electronics and suitable for telecom line card control, industrial PLC I/O expansion, and embedded memory mapping requiring stable component supply across long-lifecycle production programs.

Supply support for 74LCX139TTR 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, delivering silicon solutions for automotive, industrial, and consumer markets since 1987.

The 74LCX logic family was engineered for low-voltage, high-speed interoperability between 3.3V systems and legacy 5V infrastructure - targeting telecom, industrial control, and computing backplane applications.

FAQ

Is 74LCX139TTR pin-compatible with standard 74LS139?

Yes - it uses identical pinout and logic function as the 74139 family, including active-low outputs and dual-decoder architecture. However, it operates at 2.0–3.6V (not 5V) and features 5V-tolerant inputs, enabling drop-in replacement in many 5V-designed boards where VCC is migrated to 3.3V.

Can 74LCX139TTR drive LEDs directly?

No - its outputs are active-low and designed for logic-level interfacing, not constant-current LED drive. While ±24mA drive exceeds typical LED forward current (10–20mA), the lack of current regulation, thermal derating, and absence of built-in current-limiting resistors make direct LED connection unsafe and non-compliant with recommended usage.

What is the significance of "power-down protection" in this device?

Power-down protection ensures that inputs and outputs remain high-impedance and non-destructive when VCC = 0V - preventing back-current flow from live 5V signal lines into an unpowered subsystem. This avoids latch-up, false triggering, and damage during hot-swap or partial-power-down sequences in modular equipment.

Does 74LCX139TTR support mixed-voltage operation on the same device?

Yes - all inputs tolerate 0–5.5V regardless of VCC (2.0–3.6V), allowing simultaneous connection to 5V microcontrollers and 3.3V FPGAs. Outputs swing rail-to-rail between GND and VCC, so output logic levels match the 3.3V domain - enabling clean interfacing without external translators.