STMicroelectronics 74VHCT138AMTR

Overview

74VHCT138AMTR from STMicroelectronics is a high-speed CMOS 3-to-8 line decoder (inverting) with TTL-compatible inputs, operating at 4.5–5.5 V, 7.6 ns typical propagation delay, ±8 mA output drive, and 4 µA max quiescent current. It serves as an address decoder in memory systems, enabling selective activation of one of eight outputs based on three binary inputs and three enable signals.

For engineers reviewing the 74VHCT138AMTR datasheet, 74VHCT138AMTR pinout, 74VHCT138AMTR application, or 74VHCT138AMTR equivalent, key selection criteria include input voltage thresholds (VIH ≥ 2 V, VIL ≤ 0.8 V), symmetrical output drive (|IOH| = IOL ≥ 8 mA), power-down protection (0–7 V input tolerance), latch-up immunity, and TSSOP-16 package compatibility with legacy 74-series footprint.

Technical Context

The device implements a fully decoded 3-input logic function with active-low outputs and three independent enable inputs (G1, G2A, G2B) that support cascading for larger decoding trees. Its inverting architecture ensures only one output goes low per valid input combination when enabled.

Designed for mixed-voltage interfacing, it accepts 0–7 V on all inputs regardless of VCC, features TTL-level input thresholds, and provides ESD immunity up to 2 kV. Propagation delays are balanced (tPLH ≅ tPHL) and specified under 15 pF and 50 pF load conditions.

Key Specifications

Pinout & Package

TSSOP-16 package: 4.4 mm × 5.0 mm body, 0.65 mm pitch, 1.2 mm height, lead-free and RoHS-compliant.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 3-to-8 decoder applications.

Compared with 74HC138PW and SN74LV138APWR, the 74VHCT138AMTR uniquely combines 5 V TTL compatibility, 0–7 V input tolerance, and ultra-low ICC - making it optimal for legacy 5 V systems requiring robustness, low static power, and seamless integration without redesign.

Availability

74VHCT138AMTR is available at Aetrix Electronics and suitable for memory address decoding, peripheral select logic, I/O port expansion, and mixed-voltage interface applications requiring stable component supply and long-term industrial availability.

Supply support for 74VHCT138AMTR 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 innovative silicon solutions for automotive, industrial, and consumer markets since 1987.

The VHCT logic family targets high-speed, low-power 5 V digital systems requiring TTL compatibility and enhanced robustness - specifically engineered for memory control, bus interfacing, and industrial control logic where reliability and pin compatibility are critical.

FAQ

Can 74VHCT138AMTR operate with a 3.3 V supply?

No. The 74VHCT138AMTR is specified only for 4.5–5.5 V operation per its Recommended Operating Conditions table. At 3.3 V, input thresholds (VIH ≥ 2 V) may not be reliably met, and output drive strength degrades significantly. For 3.3 V systems, consider SN74LV138APWR instead.

What does "power-down protection" mean for this device?

Power-down protection means all inputs and outputs tolerate voltages from −0.5 V to +7.0 V even when VCC = 0 V. This prevents damage or leakage during power sequencing, hot insertion, or fault conditions - eliminating need for external diode clamps in systems with asynchronous power rails.

Is the 74VHCT138AMTR pin-compatible with 74LS138?

Yes. Pin numbering, pin functions (A/B/C, G1/G2A/G2B, Y0–Y7, VCC, GND), and logic behavior are identical to 74LS138. However, 74VHCT138AMTR draws far less quiescent current (4 µA vs. ~20 mA) and offers superior noise immunity and latch-up resistance.

Why does the truth table show "X" for some enable combinations?

"X" denotes "don't care" - meaning the corresponding input can be either high or low without affecting the output state. For example, when G1 = L (low), the decoder is disabled regardless of A/B/C values, so those inputs are irrelevant and marked X in that row of the truth table.