Texas Instruments SN74CBT3257CPWR

Overview

SN74CBT3257CPWR from Texas Instruments is a 4-bit 1-of-2 FET bus switch with bidirectional data flow, 3 Ω typical ON-state resistance (ron), <0.24 ns propagation delay at VCC = 4 V, and −2 V undershoot protection on A/B ports - deployed in USB interface signal gating and I²C bus expansion.

For engineers reviewing the SN74CBT3257CPWR datasheet, SN74CBT3257CPWR pinout, SN74CBT3257CPWR application, or SN74CBT3257CPWR equivalent, key selection criteria include Ioff partial-power-down support, 0–5-V data I/O level compatibility, TSSOP-16 package thermal performance (θJA = 108°C/W), and OE/S-controlled 4-channel switching logic.

Technical Context

The SN74CBT3257CPWR implements four independent analog/digital SPDT switches using low-threshold FETs, each controlled by a shared select (S) input and global output-enable (OE). Its active undershoot-protection circuitry clamps A/B port voltages to −2 V during negative transients while maintaining OFF-state isolation.

It supports mixed-voltage system interfacing across 0.8 V to 5 V logic families, features 5.5 pF typical OFF-state B-port capacitance for minimal signal distortion, and guarantees Ioff leakage ≤10 µA when VCC = 0 V - enabling safe backdrive isolation during partial power-down.

Key Specifications

Pinout & Package

TSSOP-16 package (PW), 4.4 mm × 5.0 mm body, 1.2 mm max height, 0.65 mm lead pitch, exposed pad not present - optimized for compact PCB layouts and standard reflow profiles (MSL Level-1).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74CBTD3384CPWR and TS3A27518EPWR, the SN74CBT3257CPWR uniquely balances ultra-low propagation delay, −2 V undershoot protection, and 4–5.5 V operation - making it optimal for robust 5-V bus isolation where signal fidelity and transient resilience are prioritized over voltage translation.

Availability

SN74CBT3257CPWR is available at Aetrix Electronics and suitable for USB interface design, I²C bus expansion, low-distortion audio gating, and multi-voltage logic translation requiring stable component supply and long-term production continuity.

Supply support for SN74CBT3257CPWR 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 connectivity technologies - with over 50 years of innovation in high-performance logic and interface solutions.

The SN74CBT3257CPWR belongs to TI's CBT (Crosspoint Bus Transceiver) family, engineered for high-speed, low-distortion signal routing in computing, communications, and industrial control systems where timing integrity and robustness are critical.

FAQ

What is the maximum data rate supported by the SN74CBT3257CPWR?

The SN74CBT3257CPWR does not specify a maximum data rate in its datasheet; instead, it guarantees <0.24 ns propagation delay and 5.5 pF OFF-state capacitance. These parameters enable reliable operation at USB Full-Speed (12 Mbps) and I²C Fast-Mode Plus (1 Mbps) rates. For higher-speed protocols like USB High-Speed, board layout and load capacitance become dominant limiting factors - not the SN74CBT3257CPWR itself.

Does the SN74CBT3257CPWR require external pull-up resistors on OE or S inputs?

Yes - to ensure a defined high-impedance state during power-up or power-down, OE must be tied to VCC via a pull-up resistor. The minimum value depends on the driver's sink capability; TI recommends ≥10 kΩ for standard CMOS drivers. S input may be driven directly but must never float - unused S pins should be held at VCC or GND per SCBA004 guidelines.

Can the SN74CBT3257CPWR be used with 1.8-V logic signals while powered at 5 V?

Yes - the SN74CBT3257CPWR explicitly supports 0–5-V signaling on A/B ports regardless of VCC (4–5.5 V). A 1.8-V signal applied to an A or B terminal will pass through the switch unaltered when enabled, as the FET architecture does not impose level-shifting. Control inputs (OE, S) remain 5-V tolerant and require appropriate logic thresholds.

How does the undershoot protection feature operate in the SN74CBT3257CPWR?

The SN74CBT3257CPWR integrates active undershoot-protection circuitry that monitors A/B port voltages. When a transient drops below −2 V, internal sensing triggers immediate switch disablement - forcing high-impedance isolation before damage occurs. This occurs independently of OE/S states and requires no external components, unlike passive diode clamping solutions.

Is the SN74CBT3257CPWR pin-compatible with other CBT-series devices in TSSOP-16?

No - the SN74CBT3257CPWR has a unique 4-channel 1-of-2 configuration with dedicated A/B1/B2 pins per channel and shared S/OE controls. Devices like SN74CBT3244 (octal buffer) or SN74CBT3383 (dual 4-bit bus switch) use different pinouts and logic functions. Always verify pin mapping against the specific device's top-marking (CU257C) and datasheet diagram.