Texas Instruments SN74HCT125D

Overview

SN74HCT125D from Texas Instruments is a quadruple bus buffer gate with 3-state outputs, designed for bidirectional data bus isolation and address/data line buffering in TTL-compatible 5-V digital systems. It features four independent non-inverting buffers (Y = A), 4.5–5.5-V operation, ±6-mA output drive, 12-ns typical propagation delay at 5 V/50 pF, and high-current 3-state outputs suitable for driving memory address registers or shared bus lines.

For engineers reviewing the SN74HCT125D datasheet, SN74HCT125D pinout, SN74HCT125D application, or SN74HCT125D equivalent, key selection criteria include 3-state enable timing (ten/tdis ≤ 35 ns), low ICC (≤80 µA), TTL-compatible input thresholds (VIH = 2 V, VIL = 0.8 V), and SOIC-14 package compatibility with standard PCB footprints for bus interface logic.

Technical Context

The SN74HCT125D implements four identical non-inverting buffer channels, each with an independent active-low 3-state output-enable (OE) input controlling high-impedance state entry and exit. Its HCT logic family ensures TTL voltage-level compatibility while operating from a single 5-V supply, enabling direct interfacing with legacy TTL and modern CMOS systems without level translation.

Each channel operates in three functional modes: enabled high (Y = A), enabled low (Y = A), or disabled (Y = high-Z), as defined by the OE input. The device uses silicon-gate CMOS process technology to achieve low static power consumption and robust noise immunity, with input clamp diodes and output current limits supporting reliable operation in mixed-signal environments.

Key Specifications

Pinout & Package

SN74HCT125D is housed in a 14-pin SOIC (D) package measuring 8.65 mm × 3.90 mm with 1.27-mm lead pitch and 1.75-mm maximum height, optimized for automated surface-mount assembly and thermal performance (RθJA = 138.7°C/W).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar bus buffer applications.

Compared with SN74HCT244N and 74LCX125M, the SN74HCT125D provides optimal balance of 5-V TTL compatibility, SOIC-14 footprint efficiency, and proven reliability in industrial bus interface roles-without requiring voltage translation or board redesign.

Availability

SN74HCT125D is available at Aetrix Electronics and suitable for memory address buffering, microcontroller bus isolation, legacy system interfacing, and digital test equipment signal routing requiring stable component supply and long-term industrial lifecycle support.

Supply support for SN74HCT125D 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

Texas Instruments is a global semiconductor leader delivering analog and embedded processing solutions, with over 90 years of innovation in logic, power, and signal chain technologies.

The SN74HCT125D belongs to TI's classic HCT logic family, engineered specifically for robust 5-V TTL-compatible bus interfacing in industrial, automotive, and computing applications where reliability and interoperability are critical.

FAQ

What is the recommended bypass capacitor value for SN74HCT125D?

A 0.1-µF ceramic capacitor is recommended directly between VCC and GND pins of the SN74HCT125D to suppress high-frequency supply noise. For enhanced broadband filtering, TI recommends paralleling it with a 1-µF capacitor placed near the device. Mount both capacitors as close as possible to the VCC/GND terminals to minimize inductance and ensure effective decoupling across switching frequencies up to 100 MHz.

Can SN74HCT125D operate reliably at 4.5 V supply?

Yes, SN74HCT125D is fully specified for operation at 4.5 V per its Recommended Operating Conditions. At this minimum VCC, it maintains VIH ≥ 2.0 V, VIL ≤ 0.8 V, tpd ≤ 39 ns (CL = 50 pF), and ±6-mA output drive - ensuring full functionality in systems with marginal 5-V rails or brown-out conditions. No derating is required within the –40°C to +85°C temperature range.

How should unused inputs be handled on SN74HCT125D?

All unused inputs on SN74HCT125D - including OE and A pins - must be tied to either VCC or GND to prevent floating states that cause excessive ICC, oscillation, or undefined outputs. For OE pins, tie to VCC via pull-up to guarantee high-Z default; for unused A inputs, connect to GND or VCC depending on desired default output state. Never leave any input unconnected.

Is SN74HCT125D RoHS compliant?

Yes, SN74HCT125D variants including SN74HCT125DRE4.A are RoHS compliant with lead finish NIPDAU and MSL Level-1 rating (260°C peak reflow). The part marking "HCT125" appears on the top surface, and full compliance documentation is available through TI's official product folder and material declarations. Obsolete variants like SN74HCT125D are not RoHS-compliant and should be avoided in new designs.

What is the maximum capacitive load SN74HCT125D can drive while maintaining timing specs?

SN74HCT125D is characterized for CL = 50 pF and CL = 150 pF loads. At 5.5 V and 25°C, tpd increases from 10 ns (50 pF) to 16 ns (150 pF); ten rises from 15 ns to 21 ns. For designs exceeding 150 pF, timing margins must be verified empirically. TI does not specify performance beyond 150 pF, and signal integrity degradation may occur above this limit without series termination or buffer staging.