STMicroelectronics 74VHCT138ATTR

Overview

74VHCT138ATTR from STMicroelectronics is a high-speed CMOS 3-to-8 line decoder (inverting) with TTL-compatible inputs, 7.6 ns typical propagation delay at 5 V, ±8 mA output drive, and operation across 4.5–5.5 V. It implements address decoding in memory systems using three binary select inputs (A/B/C) and three enable inputs (G1, G2A, G2B), with all outputs active-low.

For engineers reviewing the 74VHCT138ATTR datasheet, 74VHCT138ATTR pinout, 74VHCT138ATTR application, or 74VHCT138ATTR equivalent, key selection criteria include enable logic configuration (G1 low / G2A or G2B high disables), symmetrical output impedance, power-down input/output protection, and 0–7 V input tolerance independent of VCC.

Technical Context

This device uses sub-micron silicon gate C2MOS technology to achieve high speed and low static power (4 µA max ICC). Its inverting decoder logic maps three binary address bits to one of eight active-low outputs, conditioned by three independent enable inputs that support cascading in multi-level memory decoding architectures.

The input structure incorporates TTL threshold compatibility (VIH ≥ 2 V, VIL ≤ 0.8 V), ESD protection (2 kV HBM), and overvoltage-tolerant inputs (–0.5 V to +7.0 V), enabling safe interfacing between 5 V and 3 V systems without level shifters.

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 SN74HCT138DR and 74LVC138APW, the 74VHCT138ATTR uniquely combines 5 V operation, 7.6 ns speed, TSSOP-16 compactness, and full 0–7 V input tolerance-making it optimal for industrial 5 V designs needing cascade flexibility and robust hot-swap behavior.

Availability

74VHCT138ATTR is available at Aetrix Electronics and suitable for memory address decoding, peripheral selection, I/O expansion, and legacy system interfacing requiring stable component supply and long-term industrial availability.

Supply support for 74VHCT138ATTR 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, designing and manufacturing analog, digital, and mixed-signal ICs for automotive, industrial, and consumer markets.

The VHCT logic family targets high-speed, low-power 5 V CMOS applications with TTL compatibility and enhanced robustness-specifically engineered for reliable address decoding and control logic in mission-critical embedded systems.

FAQ

What is the maximum clock frequency supported by the 74VHCT138ATTR?

The 74VHCT138ATTR is not a clocked device-it has no internal clock and operates asynchronously. Its usable switching frequency depends on propagation delay and system timing margins; with 7.6 ns tPD, it supports address decode cycles up to ~100 MHz in well-designed layouts with controlled trace lengths and proper decoupling.

Can the 74VHCT138ATTR drive LEDs directly?

Yes. Each active-low output can sink up to 8 mA continuously, sufficient to drive standard 5 V LEDs with appropriate current-limiting resistors (e.g., 330 Ω for ~12 mA peak, derated to 8 mA). Do not exceed 8 mA per output or 50 mA total package current to avoid thermal stress.

Is the 74VHCT138ATTR pin-compatible with older 74LS138 devices?

Yes-pinout and logic function are identical to 74LS138, including A/B/C, G1/G2A/G2B, and Y0–Y7 assignments. However, VHCT offers superior noise immunity, lower power, and wider input voltage tolerance, making it a drop-in upgrade for LS-based designs without circuit modification.

Does the 74VHCT138ATTR require external pull-up resistors on its outputs?

No. Outputs are push-pull CMOS, not open-drain. They actively drive both high and low states. Pull-ups are unnecessary and would cause contention when outputs go low, risking excessive current and logic malfunction.