STMicroelectronics M74HC238B1R

Overview

M74HC238B1R from STMicroelectronics is a high-speed CMOS 3-to-8 line decoder with active-high G1 and active-low G2A/G2B enable inputs, operating across 2V–6V supply, delivering 15ns typical propagation delay at 6V, ±4mA output drive, and 4µA max quiescent current at 25°C - used in memory address decoding and digital logic control systems.

For engineers reviewing the M74HC238B1R datasheet, M74HC238B1R pinout, M74HC238B1R application, or M74HC238B1R equivalent, key selection criteria include enable input logic polarity (G1 high-active, G2A/G2B low-active), symmetrical output impedance, wide VCC range, noise immunity (28% VCC), and DIP-16 package compatibility with legacy 74-series layouts.

Technical Context

This decoder implements combinational logic where three binary inputs (A, B, C) select one of eight outputs (Y0–Y7) when enabled; decoding is inhibited if G1 is low or either G2A or G2B is high - enabling hierarchical cascade in multi-chip memory systems. All inputs feature ESD protection diodes rated for ±20mA transient current.

Propagation delays are balanced (tPLH ≅ tPHL) across all input-to-output paths (A/B/C→Y, G1→Y, G2→Y), with worst-case tPHL/tPLH ≤38ns at 6V over –55°C to +125°C. Output voltage levels meet VOH ≥5.68V and VOL ≤0.40V at 6V/5.2mA, supporting TTL- and CMOS-level interfacing.

Key Specifications

Pinout & Package

Package: Plastic DIP-16 (0.300" width), JEDEC MS-001, body dimensions 20.0 × 8.5 × 3.3 mm.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC238N and 74AHC238D, M74HC238B1R offers superior high-temperature operation (125°C), full 6V tolerance, and DIP-16 compatibility - making it optimal for industrial retrofits and automotive under-hood use where thermal margin and mechanical interchangeability are critical.

Availability

M74HC238B1R is available at Aetrix Electronics and suitable for memory address decoding, industrial I/O expansion, and automotive body control applications requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for M74HC238B1R 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, MCU, power, and discrete components for industrial, automotive, and consumer markets.

M74HC238B1R belongs to the M74HC high-speed CMOS logic family, engineered for pin-compatible upgrades of legacy 74LS devices while delivering lower power, wider voltage range, and enhanced noise immunity in industrial control and automotive electronics.

FAQ

What are the logic polarities of the enable inputs on M74HC238B1R?

G1 is active-high: decoding occurs only when G1 = HIGH. G2A and G2B are both active-low: decoding is enabled only when G2A = LOW AND G2B = LOW. If G1 is LOW, or either G2A or G2B is HIGH, all outputs (Y0–Y7) are forced LOW regardless of A/B/C states.

Can M74HC238B1R operate at 3.3V and interface with 3.3V microcontrollers?

Yes - M74HC238B1R is fully specified from 2V to 6V, including 3.3V operation. At VCC = 3.3V, VIH = 2.31V (70% VCC) and VIL = 0.99V (30% VCC), ensuring reliable recognition of standard 3.3V CMOS logic levels from microcontrollers like STM32 or ESP32.

Is M74HC238B1R compatible with 74LS238 in terms of timing and drive strength?

It is functionally and pin-compatible, but not timing-identical: M74HC238B1R has faster typical propagation (15ns vs. ~25ns for 74LS238) and stronger drive (±4mA vs. ±8mA for LS, but with lower voltage drop). Its 4µA ICC is drastically lower than LS's ~20mA, reducing heat and supply load.

Does M74HC238B1R require external pull-up resistors on its outputs?

No - outputs are push-pull CMOS with active HIGH assertion; no pull-ups are needed. Each Yx output sources up to 4mA when HIGH and sinks up to 4mA when LOW. Pull-ups would conflict with the internal driver and risk excessive current if Yx is driven LOW while pulled up.