Texas Instruments SN74CBT3257CPW

Overview

SN74CBT3257CPW from Texas Instruments is a 4-bit 1-of-2 FET multiplexer/demultiplexer with bidirectional signal routing, 3 Ω typical ON-state resistance, near-zero propagation delay (0.15 ns at 5 V), and undershoot protection up to −2 V on A/B ports - used for USB interface signal gating and bus isolation in mixed-voltage systems.

For engineers reviewing the SN74CBT3257CPW datasheet, SN74CBT3257CPW pinout, SN74CBT3257CPW application, or SN74CBT3257CPW equivalent, key selection criteria include Ioff partial-power-down support, 0–5-V data I/O compatibility across 0.8-V to 5-V logic families, TSSOP-16 package thermal performance (θJA = 108°C/W), and guaranteed −40°C to 85°C operation.

Technical Context

The SN74CBT3257CPW implements four independent analog/digital SPDT switches controlled by a shared select (S) input and global output-enable (OE) signal. Each switch uses low-threshold FETs with active undershoot-protection circuitry that clamps transient excursions below −2 V while maintaining high-impedance isolation.

It supports full 0–5-V signaling on data I/Os regardless of VCC (4–5.5 V), accepts TTL- or CMOS-level control inputs, and features Ioff current limiting (<10 µA at VCC = 0) to prevent backflow during partial power-down - critical for hot-swap and system-level power sequencing.

Key Specifications

Pinout & Package

TSSOP-16 package (PW), 5.0 mm × 4.4 mm × 1.2 mm height, 0.65 mm lead pitch, exposed pad not present, RoHS-compliant NiPdAu finish, MSL Level-1.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar FET multiplexer applications.

Compared with SN74CBT3257CPW, SN74CBTD3384PW trades undershoot immunity and 5-V compatibility for bus-hold functionality, while TS3A226AEYFFR sacrifices voltage range and transient protection to achieve lower ron and smaller footprint - making SN74CBT3257CPW the optimal choice for industrial 5-V mixed-signal isolation.

Availability

SN74CBT3257CPW is available at Aetrix Electronics and suitable for USB interface design, industrial bus isolation, low-distortion audio routing, and automated test equipment requiring stable component supply across extended temperature ranges.

Supply support for SN74CBT3257CPW 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 broad industrial, automotive, and communications market reach.

The SN74CBT3257CPW belongs to TI's CBT (Crossbar Bus Transceiver) logic family, engineered for high-speed, low-distortion signal routing in mixed-voltage digital and analog systems requiring robust ESD and transient immunity.

FAQ

What is the maximum undershoot voltage the SN74CBT3257CPW can withstand on its A/B ports?

The SN74CBT3257CPW provides active undershoot protection up to −2 V on both A and B ports, verified per datasheet SCDS137 Figure 2 and undershoot characteristics table. This protection operates independently of VCC and remains effective even during partial power-down, ensuring reliable isolation without external clamping components. The SN74CBT3257CPW maintains high-impedance state under these conditions to prevent latch-up or damage.

Does the SN74CBT3257CPW support true bidirectional signal flow between A and B ports?

Yes, the SN74CBT3257CPW supports fully bidirectional signal flow - data can pass equally well from A to B or B to A with identical electrical characteristics (3 Ω ron, 5.5 pF Cio(OFF), <0.25 ns tpd). Its FET-based architecture imposes no directionality constraint, making it suitable for analog signal routing, differential bus switching, and legacy interface bridging where signal polarity or source/sink roles may vary dynamically. This behavior is confirmed in the functional description and logic diagram of SN74CBT3257CPW.

Can the SN74CBT3257CPW operate with a 3.3-V supply voltage?

No, the SN74CBT3257CPW requires a minimum VCC of 4 V per the recommended operating conditions table in SCDS137. Operation below 4 V is not specified and may result in undefined switching behavior, increased ron, or failure to meet undershoot protection thresholds. For 3.3-V systems, consider alternatives like SN74CBTD3384PW or TS3A226AEYFFR - but note these lack the SN74CBT3257CPW's −2 V undershoot immunity and 5-V compatibility.

What is the thermal performance of the SN74CBT3257CPW in its TSSOP-16 (PW) package?

The SN74CBT3257CPW in TSSOP-16 (PW) package has a junction-to-ambient thermal resistance (θJA) of 108°C/W, as specified in the absolute maximum ratings table of SCDS137. This value assumes standard JEDEC high-K board conditions (2s2p); actual performance improves with copper pour and thermal vias. At 100 mA continuous switch current and 5 V VCC, self-heating remains below 1.2°C - well within the −40°C to 85°C operating range. No heatsinking is required for typical use cases.

How does the Ioff feature of the SN74CBT3257CPW protect downstream circuitry during power-down?

The Ioff feature limits current flow to <10 µA when VCC = 0 V, preventing damaging back-current from live signal lines into a powered-down device. This enables safe partial-power-down operation in multi-rail systems - for example, isolating a 5-V sensor bus while the microcontroller enters deep sleep. Unlike passive isolation, the SN74CBT3257CPW actively disables internal conduction paths, eliminating the need for external blocking diodes or MOSFETs. This behavior is validated in the electrical characteristics table under Ioff test conditions.