Texas Instruments SN74AHCT125DRE4

Overview

SN74AHCT125DRE4 from Texas Instruments is a quadruple 3-state bus buffer gate IC used for digital signal routing, isolation, and level translation in logic interface circuits. It features four independent channels, TTL-compatible inputs (VIH = 2 V, VIL = 0.8 V), 5-V supply operation, ±8 mA output drive, and high-impedance outputs when enabled low. It is commonly deployed in microcontroller GPIO expansion, LED driver control, and switch debouncing circuits.

For engineers reviewing the SN74AHCT125DRE4 datasheet, SN74AHCT125DRE4 pinout, SN74AHCT125DRE4 application, or SN74AHCT125DRE4 equivalent, key selection criteria include its 3-state output architecture, SOIC-14 package compatibility, commercial temperature range (–40°C to +85°C), and direct replacement suitability for legacy 74-series logic in mixed-voltage systems.

Technical Context

The SN74AHCT125DRE4 implements four identical non-inverting buffer gates, each with an independent active-low output-enable (OE) input. When OE is low, the A→Y path conducts with propagation delay ≤6.5 ns (CL = 15 pF); when OE is high, Y enters high-impedance state-enabling bus sharing without contention. Its CMOS output stage delivers rail-to-rail swing with defined VOH ≥3.8 V and VOL ≤0.44 V at IOL/IOH = ±8 mA.

Input structure is TTL-voltage compatible, accepting 0.8 V/2.0 V thresholds across VCC = 4.5–5.5 V, eliminating need for external level shifters when interfacing with legacy 5-V TTL sources. Latch-up immunity exceeds 250 mA per JESD17, and static current consumption remains ≤20 µA at 5.5 V, supporting low-power system design.

Key Specifications

Pinout & Package

SN74AHCT125DRE4 is packaged in a 14-pin SOIC (D) body measuring 8.65 mm × 3.91 mm × 1.75 mm, RoHS-compliant, with NiPdAu lead finish and MSL Level-1 rating.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LVC125A and 74HC125, SN74AHCT125DRE4 uniquely bridges 5-V TTL and CMOS domains without external components-making it the only drop-in solution for legacy system upgrades where input compatibility and pinout retention are mandatory.

Availability

SN74AHCT125DRE4 is available at Aetrix Electronics and suitable for industrial control panels, test equipment interfaces, and consumer appliance logic subsystems requiring stable component supply and long-term obsolescence management.

Supply support for SN74AHCT125DRE4 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 specializing in analog, embedded processing, and logic solutions, with decades of heritage in industry-standard logic families.

SN74AHCT125DRE4 belongs to TI's AHCT logic series-designed specifically to replace obsolete 74LS devices in 5-V systems while delivering CMOS efficiency, TTL compatibility, and enhanced ESD/latch-up robustness.

FAQ

What is the function of the OE pins on SN74AHCT125DRE4?

Each OE pin (1OE through 4OE) is an active-low control input that places the corresponding buffer output (1Y–4Y) into high-impedance state when driven high. When OE is low, the input (1A–4A) passes directly to the output. This enables independent or grouped bus isolation-critical for preventing signal contention in shared data paths. The SN74AHCT125DRE4 requires no external pull-up on OE for basic operation, though tying OE to VCC via resistor ensures safe high-Z state during power-up.

Can SN74AHCT125DRE4 operate with a 3.3-V supply?

No, SN74AHCT125DRE4 is specified only for VCC = 4.5 V to 5.5 V. Its TTL-compatible input thresholds (VIH = 2.0 V, VIL = 0.8 V) and output drive characteristics are validated exclusively within this range. Operating below 4.5 V risks failure to recognize TTL-high inputs or meet VOH/VOL specifications. For 3.3-V systems, consider SN74LVC125A instead-but note it lacks native TTL input compatibility.

What is the maximum capacitive load SN74AHCT125DRE4 can drive while meeting datasheet timing?

SN74AHCT125DRE4 guarantees full switching performance-including tPLH/tPHL ≤6.5 ns and tPZH/tPHZ ≤8 ns-with CL = 15 pF. At CL = 50 pF, delays increase to ≤8.5 ns (A→Y) and ≤10 ns (OE→Y), remaining within specification. TI explicitly states that loads >50 pF are not recommended, as timing degradation accelerates nonlinearly and output voltage margins may erode due to increased IOL/IOH demand.

How should unused inputs be handled on SN74AHCT125DRE4?

All unused inputs-including A pins and OE pins-must be terminated to a valid logic level: either VCC or GND. Floating CMOS inputs cause excessive ICC, oscillation, and potential device damage. A 10-kΩ pull-up or pull-down resistor is recommended for unused OE pins to ensure predictable high-Z behavior; unused A inputs may be tied directly to VCC or GND depending on desired default output state. Never leave any input unconnected.

Is SN74AHCT125DRE4 pin-compatible with other 74-series 125 variants?

Yes, SN74AHCT125DRE4 shares identical pinout (SOIC-14) and logic function with SN74LS125, SN74ALS125, and SN74F125. However, electrical behavior differs: SN74AHCT125DRE4 draws less ICC, offers higher noise immunity, and accepts TTL inputs without external biasing. While it can replace older 125s in most layouts, verify timing margins and fan-out requirements-especially in high-speed or high-noise environments-since propagation delays and output drive strength differ.