Texas Instruments CD74HCT125E

Overview

CD74HCT125E from Texas Instruments is a quadruple 3-state buffer IC used for digital signal routing and bus isolation in TTL- and CMOS-compatible systems. It features four independent non-inverting buffers (Y = A), 4.5V–5.5V supply operation, –55°C to +125°C temperature range, and LSTTL-input-compatible thresholds (VIL ≤ 0.8 V, VIH ≥ 2 V). It enables controlled data path activation in 4-bit parallel buses.

For engineers reviewing the CD74HCT125E datasheet, CD74HCT125E pinout, CD74HCT125E application, or CD74HCT125E equivalent, key selection considerations include 3-state output timing (tpd = 31 ns typ at 4.5 V), low quiescent current (ICC = 8 µA typ), thermal performance (RθJA = 103.8 °C/W in PDIP), and compatibility with legacy TTL logic levels.

Technical Context

The CD74HCT125E implements four identical non-inverting buffer gates, each with an active-low 3-state output enable (OE) controlling high-impedance (Z) or driven (H/L) output states. Its TTL-compatible inputs accept 0.8 V/2.0 V thresholds while drawing ≤1 µA leakage, enabling direct interfacing with bipolar logic without level shifters.

Each channel operates independently: input A drives output Y when OE is low; output enters high-impedance state when OE is high. The device supports fanout of up to 10 LSTTL loads and exhibits balanced sourcing/sinking capability (IOH/ IOL = ±4 mA at VOH/VOL limits), critical for clean signal integrity on shared buses.

Key Specifications

Pinout & Package

CD74HCT125E is supplied in a 14-pin plastic dual in-line package (PDIP-N), with 19.30 mm × 9.4 mm footprint and 19.30 mm × 6.35 mm body size. Pin 7 is GND and pin 14 is VCC; all four channels follow identical 1OE/1A/1Y, 2OE/2A/2Y, 3OE/3A/3Y, 4OE/4A/4Y ordering.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HCT125N and MC74HCT125ANG, CD74HCT125E offers identical core functionality and timing but is specifically characterized for extended temperature operation and widely stocked in PDIP packaging-making it optimal for legacy board replacements and high-reliability industrial designs where long-term availability matters.

Availability

CD74HCT125E is available at Aetrix Electronics and suitable for industrial control systems, automotive engine management modules, and test equipment requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for CD74HCT125E 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 company headquartered in Dallas, Texas, specializing in analog and embedded processing technologies with over 90 years of innovation in logic, power management, and signal chain solutions.

The CD74HCT125E belongs to TI's HCT (High-Speed CMOS TTL-compatible) logic family, designed specifically to replace legacy 74LS devices with lower power, higher noise immunity, and seamless 5 V system integration.

FAQ

What is the maximum capacitive load the CD74HCT125E can drive while maintaining specified timing?

The CD74HCT125E is characterized for CL = 50 pF in its switching specifications, with tpd = 31 ns typical at 4.5 V. While it can drive larger loads (e.g., 70 pF per layout guidelines), exceeding 50 pF increases propagation delay nonlinearly and may degrade edge integrity. For designs requiring >50 pF, add a series resistor to limit peak output current and avoid violating the ±35 mA absolute maximum rating. The CD74HCT125E datasheet specifies performance only up to 50 pF in timing tables.

Does the CD74HCT125E support mixed-voltage operation, such as 3.3 V inputs with a 5 V supply?

Yes-the CD74HCT125E accepts 3.3 V logic inputs when powered at 5 V, because its VIH(min) = 2.0 V and VIL(max) = 0.8 V are well within 3.3 V logic high/low ranges. Input leakage remains ≤1 µA, and no level-shifting is needed. However, outputs swing rail-to-rail (0 V to 5 V), so downstream 3.3 V receivers must tolerate 5 V inputs or include clamping. The CD74HCT125E does not support sub-4.5 V supply operation.

How should unused inputs and outputs be handled on the CD74HCT125E?

Unused inputs must be terminated to VCC or GND-never left floating-to prevent undefined logic states and excessive current draw. A 10 kΩ pull-up or pull-down resistor is recommended for flexibility. Unused outputs may be left unconnected (floating) since the CD74HCT125E's 3-state architecture isolates them when OE is high; do not tie outputs directly to VCC or GND, as this risks violating the ±35 mA output current limit and damaging the CD74HCT125E.

What is the thermal resistance (RθJA) of the CD74HCT125E in its PDIP package?

The CD74HCT125E in the 14-pin PDIP (N) package has a junction-to-ambient thermal resistance (RθJA) of 103.8 °C/W, measured under standard JEDEC test conditions (single-layer board, no airflow). This value assumes proper PCB copper area and thermal vias are used; actual board-level RθJA may vary. The CD74HCT125E's maximum junction temperature is 150 °C, so at 160 µA max ICC and 5.5 V, self-heating remains negligible-no heatsink is required for typical operation.

Can the CD74HCT125E be used in place of the older 74LS125 in existing designs?

Yes-the CD74HCT125E is a direct drop-in replacement for the 74LS125 in 5 V systems: identical pinout, same 3-state buffer function, compatible input thresholds (VIL ≤ 0.8 V, VIH ≥ 2.0 V), and improved parameters including lower ICC (8 µA vs. ~15 mA), wider temperature range (–55°C to +125°C vs. 0°C to +70°C), and higher noise immunity. No PCB changes are required, and the CD74HCT125E enhances reliability and power efficiency without design modification.