Texas Instruments SN74HCT125N

Overview

SN74HCT125N from Texas Instruments is a quadruple 3-state bus buffer gate IC with TTL-compatible inputs and independent enable control per channel, operating at 4.5–5.5 V, delivering ±6-mA output drive, 12-ns typical propagation delay, and 80-µA max supply current - used for bidirectional data bus isolation in microcontroller peripheral interfaces.

For engineers reviewing the SN74HCT125N datasheet, SN74HCT125N pinout, SN74HCT125N application, or SN74HCT125N equivalent, key selection criteria include 3-state output timing (ten/tdis), thermal resistance (RθJA = 75.3°C/W), PDIP-14 package compatibility, and HCT logic family noise immunity with LSTTL load driving capability.

Technical Context

The SN74HCT125N implements four identical non-inverting buffer gates (Y = A), each with an active-low 3-state output controlled by a dedicated OE input. Its HCT logic family ensures TTL-voltage compatibility (VIH = 2 V, VIL = 0.8 V) while maintaining CMOS power efficiency.

Each channel operates independently: when OE is low, the output follows the A input; when OE is high, the output enters high-impedance state. This architecture enables time-multiplexed bus sharing without contention, supporting memory address buffering and I/O expansion in industrial control systems.

Key Specifications

Pinout & Package

SN74HCT125N is housed in a 14-pin Plastic Dual In-line Package (PDIP) with 19.31 mm × 6.35 mm body size and 2.54 mm lead pitch, suitable for through-hole prototyping and industrial PCB assembly.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC125N and 74ACT125N, the SN74HCT125N uniquely balances TTL compatibility, moderate speed, and robust drive in a PDIP-14 package - making it optimal for retrofitting legacy 5-V systems without redesigning interface logic or PCB layout.

Availability

SN74HCT125N is available at Aetrix Electronics and suitable for industrial control panels, test equipment interfaces, and embedded microcontroller peripheral expansion requiring stable component supply and long-term obsolescence management.

Supply support for SN74HCT125N 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 U.S.-based semiconductor company specializing in analog, embedded processing, and logic solutions with over 50 years of industrial-grade product development.

The SN74HCT125N belongs to TI's 74HCT logic family - designed specifically for seamless integration between TTL-based legacy systems and modern CMOS-based controllers while maintaining low power and high noise immunity.

FAQ

What is the maximum operating temperature range for the SN74HCT125N?

The SN74HCT125N is rated for operation from –40°C to +85°C ambient temperature, as specified in its Recommended Operating Conditions table. This industrial temperature range ensures reliable performance in factory automation, test instrumentation, and outdoor embedded systems where thermal cycling occurs. The device's RθJA of 75.3°C/W allows safe operation at full output drive within this range when proper PCB copper area and airflow are maintained.

Can the SN74HCT125N be used with a 3.3-V microcontroller I/O?

No - the SN74HCT125N requires a 4.5–5.5-V supply and has TTL-compatible inputs (VIH = 2.0 V min), but its outputs swing rail-to-rail at 5 V and are not 3.3-V tolerant. Direct connection to a 3.3-V microcontroller risks overvoltage damage to the MCU inputs. To interface with 3.3-V logic, use a level-shifter IC or a 3.3-V–compatible buffer like the SN74LVC125A, not the SN74HCT125N.

How does the SN74HCT125N differ from the SN74HCT244N?

The SN74HCT125N contains four independent non-inverting buffers, each with its own 3-state enable (OE), whereas the SN74HCT244N integrates eight buffers grouped into two 4-bit sections with shared OE controls per section. The SN74HCT125N offers finer-grained channel control ideal for discrete signal gating, while the SN74HCT244N targets parallel bus buffering where group enable suffices. Pinout, package, and electrical specs also differ - they are not interchangeable.

Is a bypass capacitor required for stable operation of the SN74HCT125N?

Yes - TI recommends a 0.1-µF ceramic bypass capacitor placed as close as possible to the VCC and GND pins of the SN74HCT125N. This suppresses high-frequency supply noise generated during output switching, preventing false triggering or increased propagation delay variation. For noisy environments, paralleling with a 1-µF capacitor further improves low-frequency decoupling. Omitting the capacitor may cause erratic behavior, especially at higher bus toggle rates.

What happens to the output of the SN74HCT125N when OE is left floating?

If any OE pin on the SN74HCT125N is left unconnected, it may float to an indeterminate voltage near the logic threshold, causing partial turn-on of the output driver - resulting in excessive current draw, overheating, bus contention, or unpredictable logic states. TI explicitly requires all unused inputs (including OE) to be tied to VCC or GND. For OE, tie to VCC via a pull-up resistor (e.g., 10 kΩ) to ensure default high-Z state during power-up and prevent unintended activation.