STMicroelectronics M74HC126B1R

Overview

M74HC126B1R from STMicroelectronics is a high-speed CMOS quad 3-state bus buffer, designed for bidirectional data bus isolation and signal conditioning in digital systems. It operates across 2 V to 6 V, delivers 8 ns typical propagation delay at 6 V, supports ±6 mA output drive, and features symmetrical output impedance and high noise immunity (28 % VCC min). It is used in industrial control backplanes and microcontroller I/O expansion interfaces.

For engineers reviewing the M74HC126B1R datasheet, M74HC126B1R pinout, M74HC126B1R application, or M74HC126B1R equivalent, key selection criteria include 3-state enable timing (tPZL/tPLZ ≤ 19 ns), wide temperature range support (–55 °C to +125 °C), SO14/TSSOP14 package compatibility, and automotive-grade variants with AEC-Q100 qualification.

Technical Context

The M74HC126B1R implements four independent non-inverting buffers, each with a dedicated active-high 3-state enable input (G). Its silicon gate C2MOS process ensures low static current (4 μA max at 25 °C) and robust ESD protection (HBM: 2 kV, CDM: 1 kV).

Each buffer exhibits balanced tPLH ≅ tPHL propagation delays and matched output drive capability (|IOH| = IOL ≥ 6 mA at VCC = 4.5 V), enabling clean signal integrity in multi-load bus environments without skew-induced timing violations.

Key Specifications

Pinout & Package

Available in SO14 (8.75 mm × 6.2 mm) and TSSOP14 (5.1 mm × 6.6 mm) packages, both RoHS-compliant and ECOPACK® certified. The SO14 variant uses standard 1.27 mm pitch; TSSOP14 uses 0.65 mm pitch for space-constrained designs.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar quad 3-state buffer applications.

Compared with SN74HC126N and 74VHC126M, the M74HC126B1R uniquely combines 6 V operation, –55 °C to +125 °C range, AEC-Q100 automotive variants, and 1 kV CDM ESD - making it optimal for ruggedized industrial and automotive bus isolation where voltage flexibility and environmental resilience are mandatory.

Availability

M74HC126B1R is available at Aetrix Electronics and suitable for industrial PLC backplanes, automotive body control modules, and test equipment digital I/O cards requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for M74HC126B1R 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 intelligent power, sensing, and control solutions for industrial, automotive, and consumer markets.

The M74HC126B1R belongs to ST's HC logic family - engineered for high noise immunity, low power, and interoperability with legacy TTL and modern CMOS systems in harsh operating environments.

FAQ

What is the maximum clock frequency supported by M74HC126B1R in bus applications?

The M74HC126B1R is not a clocked device but a combinational buffer; its usable frequency depends on propagation delay and load. With 8 ns typical tPD and 50 pF load, it supports clean signal transmission up to ~25 MHz for edge-aligned data transfers, assuming adequate setup/hold margins and proper PCB layout.

Can M74HC126B1R drive a 50 Ω transmission line directly?

No - the M74HC126B1R is not designed for 50 Ω line driving. Its 6 mA output drive corresponds to ~83 Ω dynamic impedance at 5 V, making it suitable for unterminated stubs or capacitive loads ≤50 pF. For 50 Ω lines, use a dedicated line driver or add series termination.

Is M74HC126B1R compatible with 3.3 V microcontrollers?

Yes - the M74HC126B1R operates down to 2 V and accepts 3.3 V logic levels as valid inputs (VIH = 2.1 V min at VCC = 3.3 V). When powered at 3.3 V, it outputs VOH ≥ 3.1 V and VOL ≤ 0.26 V, ensuring full compatibility with standard 3.3 V CMOS interfaces.

Does M74HC126B1R require external pull-up or pull-down resistors on enable inputs?

No - the enable inputs (1G–4G) have no internal pull resistors, but their DC input leakage is ≤±1 μA. In static configurations, external biasing is optional; however, in floating-wire scenarios (e.g., unconnected test points), a 100 kΩ pull-down is recommended to prevent unintended output enable.