Texas Instruments SN74AHC125D

Overview

SN74AHC125D from Texas Instruments is a quadruple bus buffer gate with independent 3-state outputs, designed for logic-level translation and bidirectional bus isolation in industrial control and embedded systems. It operates from 2 V to 5.5 V, supports –40°C to 125°C ambient temperature, delivers ±8 mA output drive at 5 V, and features four dedicated OE pins enabling per-channel enable/disable control - used in PLC I/O modules and PoE power management interfaces.

For engineers reviewing the SN74AHC125D datasheet, SN74AHC125D pinout, SN74AHC125D application, or SN74AHC125D equivalent, this page provides verified functional specifications, SOIC-14 package details, real-world timing behavior (tPLH ≤ 6.5 ns @ 5 V), thermal resistance (RθJA = 124.5°C/W), and validated alternative options for bus buffering in motor drives and point-of-sale terminals.

Technical Context

The SN74AHC125D implements four independent CMOS buffer gates, each with active-low output-enable (OE) control. When OE is low, the A→Y path is enabled with propagation delay as low as 3.8 ns (min) at 5 V; when OE is high, the output enters high-impedance state with leakage < ±2.5 µA. All buffers share a single VCC (2–5.5 V) and GND rail, with no internal voltage regulation or level-shifting circuitry.

Its logic behavior follows standard positive-logic truth table: OE = L enables pass-through (Y = A); OE = H forces Y = Z (high-Z). Input thresholds scale with VCC (VIH = 0.7×VCC min; VIL = 0.3×VCC max), and ESD protection meets ±1500 V HBM per JESD22-A114.

Key Specifications

Pinout & Package

SN74AHC125D uses a 14-pin SOIC (D) package measuring 8.65 mm × 3.91 mm, with standard 1.27 mm pitch and gull-wing leads. Thermal resistance is RθJA = 124.5°C/W, requiring minimal copper area for thermal management in industrial PCB layouts.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LVC125A and 74AHC125, the SN74AHC125D offers broader voltage compatibility (2–5.5 V) than the LVC variant and TI-specific qualification for extended temperature operation (–40°C to 125°C), making it preferred for automotive-adjacent industrial control where supply rails may vary across system states.

Availability

SN74AHC125D is available at Aetrix Electronics and suitable for programmable logic controllers, Power over Ethernet systems, and motor drive control modules requiring stable component supply across extended temperature ranges and multi-year production cycles.

Supply support for SN74AHC125D 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 and embedded processing solutions, with decades of experience in industrial-grade logic and interface products.

The SN74AHC125D belongs to TI's AHC logic family, engineered for high-speed, low-power bus buffering in harsh industrial environments - emphasizing wide voltage tolerance, robust ESD performance, and guaranteed operation from –40°C to 125°C.

FAQ

What is the recommended pull-up resistor value for OE pins on the SN74AHC125D?

The SN74AHC125D OE pins must be tied to VCC via a pull-up resistor during power-up to guarantee high-impedance default. The minimum value depends on the driver's current-sinking capability: for typical microcontroller GPIOs (±20 mA), a 10 kΩ resistor ensures reliable logic-high while limiting current to <0.5 mA at 5 V. TI recommends values between 4.7 kΩ and 100 kΩ depending on noise environment and rise-time requirements. The SN74AHC125D datasheet specifies no maximum value, but >1 MΩ risks slow edge rates in noisy settings.

Can the SN74AHC125D interface between 3.3 V and 5 V logic domains?

Yes, the SN74AHC125D supports mixed-voltage interfacing when powered at the higher rail (e.g., VCC = 5 V). Its inputs tolerate voltages up to 7 V, allowing direct connection to 3.3 V outputs without clamping diodes. However, outputs swing from 0 to VCC, so 5 V outputs must be level-shifted before connecting to 3.3 V inputs. For bidirectional translation, two SN74AHC125D devices with OE-controlled directionality are required - the SN74AHC125D itself does not perform automatic level shifting.

What is the maximum capacitive load the SN74AHC125D can drive reliably?

The SN74AHC125D is characterized for CL = 15 pF and 50 pF loads in its switching specifications. At 5 V VCC, it maintains tPLH ≤ 8.5 ns and output voltage swing within VOH ≥ 3.8 V / VOL ≤ 0.5 V up to 50 pF. Driving >50 pF increases propagation delay nonlinearly and may cause overshoot; TI recommends limiting total load (including trace capacitance and input capacitance of downstream devices) to ≤40 pF for timing-critical applications. The SN74AHC125D input capacitance is 10 pF max, contributing to total load budget.

Does the SN74AHC125D have built-in power-on reset behavior for OE pins?

No, the SN74AHC125D has no internal power-on reset circuitry. To ensure all outputs start in high-impedance state during power-up or power-down, OE pins must be externally pulled up to VCC using a resistor. TI specifies that the minimum pull-up value is determined by the current-sinking capability of the driving source - for example, a 10 kΩ resistor limits current to 0.5 mA at 5 V, which is well within the 25 mA absolute maximum rating. Failure to implement this external pull-up risks bus contention or undefined logic states during supply ramp.

How does temperature affect the output drive strength of the SN74AHC125D?

Output drive strength of the SN74AHC125D degrades with increasing temperature: at 125°C and VCC = 5 V, the guaranteed IOL is +4 mA (vs +8 mA at 25°C), and IOH is –4 mA (vs –8 mA). This 50% reduction is due to increased channel resistance in the output MOSFETs. Designers must verify worst-case timing (tPLH up to 8.5 ns) and voltage margins (VOH ≥ 3.8 V, VOL ≤ 0.5 V) at maximum junction temperature. The SN74AHC125D's RθJA = 124.5°C/W means 100 mW dissipation raises junction temperature by ~12.5°C above ambient - critical for thermally constrained industrial enclosures.