STMicroelectronics M74HCT125B1R

Overview

M74HCT125B1R from STMicroelectronics is a high-speed CMOS quad bus buffer with 3-state outputs, designed for TTL/NMOS-to-HC interface translation 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 125 devices. Used in address/data bus isolation and bidirectional bus control in industrial controllers and legacy embedded systems.

For engineers reviewing the M74HCT125B1R datasheet, M74HCT125B1R pinout, M74HCT125B1R application, or M74HCT125B1R equivalent, key selection factors include 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 M74HCT125B1R implements four independent non-inverting buffers, each with an active-low 3-state enable (G input) controlling output impedance. Its C2MOS silicon gate process enables TTL-level input compatibility while maintaining CMOS power efficiency and noise immunity.

All inputs include protection diodes against ESD and transient overvoltage. Propagation delays are balanced (tPLH ≅ tPHL), and output impedance is symmetrical (|IOH| = IOL ≥ 6 mA), ensuring consistent rise/fall times and predictable bus loading in multi-driver configurations.

Key Specifications

Pinout & Package

Package: Plastic DIP-14 (Dual In-line Package, 14-pin, 0.3" wide). Pin pitch: 2.54 mm. Body dimensions: 20.0 × 8.5 × 3.3 mm (L × W × H).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HCT125N and 74HCT125PW, the M74HCT125B1R offers full –55°C to +125°C operation and DIP-14 through-hole packaging-critical for legacy repair, prototyping, and high-reliability industrial deployments where thermal margin and mechanical robustness are prioritized.

Availability

M74HCT125B1R is available at Aetrix Electronics and suitable for industrial PLC backplanes, legacy microprocessor bus interfaces, and automotive ECU signal conditioning requiring stable component supply across extended temperature ranges and long product lifecycles.

Supply support for M74HCT125B1R 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 solutions with broad analog and digital portfolio coverage.

The M74HCT125B1R belongs to ST's legacy HCT logic family, engineered for seamless interoperability between TTL, NMOS, and CMOS systems in cost-sensitive, high-reliability industrial applications.

FAQ

What is the maximum clock frequency supported by the M74HCT125B1R?

The device does not operate as a clocked element but as a combinatorial buffer. Its 13 ns typical propagation delay at 4.5 V and 50 pF load supports reliable data transfer up to approximately 30 MHz in bus-switching applications. Maximum usable frequency depends on system-level timing margins, including setup/hold requirements of downstream components and PCB trace delays.

Can the M74HCT125B1R drive a 50 Ω transmission line directly?

No. With a minimum output drive of 6 mA into resistive loads, the M74HCT125B1R cannot properly terminate or drive a 50 Ω line (requiring ~100 mA for 5 V swing). It is intended for CMOS/TTL bus loading, not RF or high-speed transmission line driving. Use dedicated line drivers or impedance-matching buffers for such applications.

Is the M74HCT125B1R RoHS compliant?

Yes. As a STMicroelectronics product manufactured after July 2006 and conforming to EU Directive 2011/65/EU, the M74HCT125B1R is lead-free and RoHS compliant. The DIP-14 package uses matte tin plating on leads and halogen-free molding compound per ST's standard environmental specifications.

How does the 3-state enable timing affect bus arbitration in multi-driver systems?

With tPZL and tPLZ ≤ 36 ns (max) at VCC = 4.5 V, the M74HCT125B1R ensures rapid, deterministic transition into and out of high-impedance states. This minimizes bus turnaround time and prevents glitches during handoff between drivers-essential for reliable operation in shared-bus architectures like ISA or custom parallel control buses.