Texas Instruments SN74BCT125ANSR

Overview

SN74BCT125ANSR from Texas Instruments is a quadruple bus buffer gate with 3-state outputs, designed for bidirectional data bus isolation and memory address register buffering in 5-V TTL-compatible systems. It operates from 4.5 V to 5.5 V, features BiCMOS logic for low ICCZ (6–14 mA), and delivers ±64 mA output drive capability with propagation delays as low as 1.6 ns (tPLH) at 5 V.

For engineers reviewing the SN74BCT125ANSR datasheet, SN74BCT125ANSR pinout, SN74BCT125ANSR application, or SN74BCT125ANSR equivalent, key selection criteria include 3-state enable timing (tPZH/tPZL ≤ 10.3 ns), SOIC-NS package thermal performance (θJA = 76°C/W), and compatibility with legacy TTL-level buses requiring high-current sinking and controlled bus release.

Technical Context

This device implements four independent non-inverting buffers, each with an active-low output-enable (OE) control input. Each buffer transitions to high-impedance when its OE is high, enabling bus sharing without contention. The BiCMOS architecture combines bipolar input stages for TTL-level compatibility and CMOS output stages for reduced quiescent current.

Input thresholds are TTL-compatible (VIL = 0.8 V, VIH = 2.0 V), and outputs meet standard TTL voltage levels (VOH ≥ 2.4 V at IOL = 48 mA, VOL ≤ 0.55 V). The 14-pin SOP-NS package supports surface-mount assembly with RoHS-compliant NiPdAu lead finish and MSL Level-1 reflow rating.

Key Specifications

Pinout & Package

The SN74BCT125ANSR is housed in a 14-pin SOP (Small Outline Package) with NS designation, measuring 8.65 mm × 3.91 mm × 1.75 mm max height, RoHS-compliant NiPdAu lead finish, and MSL Level-1 moisture sensitivity rating.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS125N, SN74BCT125ANSR provides 8× higher output current and 9× faster propagation, making it essential for 5-V bus loading; versus SN74LVC125APW, it retains full TTL compatibility but requires 5-V rails and occupies a larger SOP-NS footprint.

Availability

SN74BCT125ANSR is available at Aetrix Electronics and suitable for industrial control backplanes, legacy computer bus interfaces, and memory subsystems requiring stable component supply and long-term obsolescence management.

Supply support for SN74BCT125ANSR 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 over 90 years of innovation in industrial, automotive, and communications electronics.

The 'BCT logic family was developed to bridge TTL and CMOS domains, delivering high-speed, high-drive 5-V logic with reduced power consumption-specifically targeting memory expansion, bus arbitration, and industrial control interfaces.

FAQ

What is the recommended power-up sequence for SN74BCT125ANSR to avoid bus contention?

TI recommends tying all OE inputs to VCC through a pull-up resistor (value determined by driver sink capability) before applying VCC. This ensures outputs remain in high-impedance during power ramp-up. For SN74BCT125ANSR, OE must be held high until system logic is ready to assert valid control signals-preventing unintended bus driving during reset. The device does not require special sequencing beyond this OE biasing.

Can SN74BCT125ANSR interface directly with 3.3-V microcontrollers?

No-SN74BCT125ANSR is a 5-V-only device with TTL-compatible input thresholds (VIH = 2.0 V min, VIL = 0.8 V max). While a 3.3-V logic high may exceed VIH in some cases, it violates the recommended operating conditions and risks unreliable switching. For mixed-voltage systems, use a dedicated level shifter or select a 3.3-V–tolerant buffer such as SN74LVC125A. SN74BCT125ANSR must operate with 4.5–5.5 V supply and TTL-level inputs.

What is the maximum capacitive load SN74BCT125ANSR can drive while maintaining specified timing?

TI specifies switching characteristics at CL = 50 pF, R1 = R2 = 500 Ω. While SN74BCT125ANSR can drive heavier loads (e.g., 100+ pF), propagation and enable/disable delays increase linearly with capacitance. For reliable operation at full speed, keep trace + load capacitance ≤50 pF. If higher capacitance is unavoidable, derate timing margins using the device's output resistance model (≈10 Ω typical) and verify with oscilloscope measurements on the actual SN74BCT125ANSR circuit.

Does SN74BCT125ANSR support hot-swap or live-insertion into a powered bus?

No-SN74BCT125ANSR is not hot-swap rated. Its absolute maximum ratings permit VO up to 5.5 V in the disabled state, but no protection is provided against bus transients, ground bounce, or supply sequencing during insertion. Applying VCC before establishing proper GND connection-or connecting outputs to a live bus-can exceed IOZH/IOZL limits (±50 µA) and cause latch-up. Use dedicated hot-swap controllers or buffer isolators if live insertion is required. SN74BCT125ANSR is intended for fixed, powered-system integration only.

How does the BiCMOS design of SN74BCT125ANSR reduce power consumption compared to standard TTL buffers?

SN74BCT125ANSR uses BiCMOS technology: bipolar transistors for robust TTL input stage (ensuring VIH/VIL compatibility), and CMOS output transistors for low static current. This reduces ICCZ to 6–14 mA (vs. 24+ mA in SN74LS125), cutting quiescent power by >50%. The design eliminates the base-drive current inherent in pure bipolar buffers, while retaining high-speed edge rates and drive strength-making SN74BCT125ANSR ideal for power-sensitive 5-V bus applications where LS-series alternatives would overheat.