STMicroelectronics M74HCT126B1R

Overview

M74HCT126B1R from STMicroelectronics is a high-speed CMOS quad bus buffer with 3-state outputs, designed for TTL/NMOS-to-HCMOS interfacing in digital logic systems. It features 13 ns typical propagation delay at 4.5 V, ±6 mA symmetrical output drive, and pin/function compatibility with standard 74-series 126 devices. Used in address/data bus isolation and bidirectional bus control in industrial controllers and legacy embedded systems.

For engineers reviewing the M74HCT126B1R datasheet, M74HCT126B1R pinout, M74HCT126B1R application, or M74HCT126B1R equivalent, key selection criteria include guaranteed 3-state enable timing (tPZL/tPLZ ≤ 36 ns), TTL-compatible input thresholds (VIH ≥ 2.0 V, VIL ≤ 0.8 V), and operation across –55 °C to +125 °C industrial temperature range.

Technical Context

The M74HCT126B1R implements four independent non-inverting buffers, each with an active-low 3-state enable input (G). Its C2MOS silicon gate process ensures low static current (ICC ≤ 4 µA) while maintaining TTL-level input compatibility and rail-to-rail output swing under load.

Each channel supports symmetrical output impedance (|IOH| = IOL ≥ 6 mA), balanced propagation delays (tPLH ≅ tPHL), and integrated input protection against ESD and transient overvoltage-enabling robust operation in noisy industrial environments without external clamping.

Key Specifications

Pinout & Package

Package: Plastic DIP-14 (dual in-line package, 0.3 inch width, through-hole mounting).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HCT126N and 74HCT126D, the M74HCT126B1R uniquely combines DIP-14 through-hole packaging, ultra-low quiescent current (≤4 µA), and full –55 °C to +125 °C qualification-making it optimal for ruggedized, hand-soldered, or legacy-replacement applications where thermal margin and mechanical serviceability are critical.

Availability

M74HCT126B1R is available at Aetrix Electronics and suitable for industrial PLC backplanes, legacy microprocessor bus isolation, and automotive ECU signal conditioning requiring stable component supply across extended temperature ranges and long product lifecycles.

Supply support for M74HCT126B1R 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, specializing in automotive, industrial, and power management ICs with vertical manufacturing capabilities.

The M74HCT126B1R belongs to ST's legacy HCT logic family, engineered specifically for seamless interoperability between TTL, NMOS, and CMOS systems in harsh-environment industrial and transportation applications.

FAQ

Is M74HCT126B1R pin-compatible with standard 74LS126?

Yes-M74HCT126B1R is functionally and pin-compatible with 74LS126, sharing identical pinout (DIP-14), truth table, and 3-state enable behavior. However, its CMOS input structure draws negligible DC current versus LS TTL inputs, reducing loading on upstream drivers and enabling higher fanout without buffering.

What is the maximum capacitive load this device can drive reliably?

The M74HCT126B1R is characterized up to 150 pF (per AC specs), with tPLH/tPHL ≤ 41 ns at CL = 150 pF and VCC = 4.5 V. For stable operation beyond 150 pF, series termination or reduced slew rate via RC filtering is recommended to avoid ringing and timing violations.

Does this part support mixed-voltage operation (e.g., 3.3 V inputs with 5 V supply)?

No-M74HCT126B1R is strictly a 5 V-only device. Its absolute maximum input voltage is VCC + 0.5 V, and VIH/VIL thresholds are defined for 4.5–5.5 V supply. Applying 3.3 V logic signals may result in marginal or undefined switching behavior; use 74LVC126 or level translators for true 3.3 V ↔ 5 V interfacing.

Can unused inputs be left floating?

No-unused inputs must be tied to VCC or GND. Floating CMOS inputs cause increased ICC, potential oscillation, and susceptibility to noise-induced switching. For unused channels, connect both A and G pins to VCC (output disabled) or GND (output enabled low), depending on system safety requirements.