Texas Instruments SN74CBT3257CDBR

Overview

SN74CBT3257CDBR from Texas Instruments is a 4-bit 1-of-2 FET multiplexer/demultiplexer with bidirectional signal routing, 3 Ω typical ON-state resistance, <0.24 ns propagation delay at 4 V, and −2 V undershoot protection on A/B ports. It operates from 4 V to 5.5 V and supports 0–5 V logic levels across USB interface and bus isolation applications.

For engineers reviewing the SN74CBT3257CDBR datasheet, SN74CBT3257CDBR pinout, SN74CBT3257CDBR application, or SN74CBT3257CDBR equivalent, key selection criteria include Ioff-enabled partial-power-down capability, 5.5 pF typical OFF-state B-port capacitance, TTL/CMOS-compatible control inputs, and SSOP-16 (DB) package thermal performance (θJA = 82°C/W).

Technical Context

The SN74CBT3257CDBR 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 A/B port voltages down to −2 V while maintaining OFF-state isolation.

Its Ioff feature guarantees no backflow current during partial power-down, and its 0–5 V data I/O compatibility enables level-shifting between 0.8 V, 1.2 V, 1.5 V, 1.8 V, 2.5 V, 3.3 V, and 5 V domains without external biasing. Control inputs accept TTL or 3.3/5 V CMOS logic thresholds.

Key Specifications

Pinout & Package

SN74CBT3257CDBR is housed in a 16-pin SSOP (Shrink Small Outline Package), DB variant, with 0.65 mm pitch, 7.4 mm × 5.3 mm body size, and 1.75 mm max height per JEDEC MO-150. Thermal resistance θJA = 82°C/W supports industrial ambient operation up to +85°C.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74CBT3257CDBR, SN74CBTD3384CDBR offers more channels but sacrifices transient robustness, while TS3A27518ERTER delivers lower resistance at the cost of 5 V operation and industrial reliability - making SN74CBT3257CDBR the balanced choice for mixed-voltage, hot-plug-capable industrial and computing interfaces.

Availability

SN74CBT3257CDBR is available at Aetrix Electronics and suitable for USB interface design, bus isolation architecture, and low-distortion signal gating requiring stable component supply, consistent SSOP-16 (DB) packaging, and guaranteed −40°C to +85°C industrial temperature compliance.

Supply support for SN74CBT3257CDBR 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 decades of expertise in high-speed interface solutions.

The SN74CBT3257CDBR belongs to TI's CBT (Crossbar Bus Transceiver) family, engineered for low-latency, low-distortion signal routing in mixed-signal systems where voltage-level flexibility and transient resilience are essential.

FAQ

What is the maximum undershoot voltage the SN74CBT3257CDBR can withstand on its A and B ports?

The SN74CBT3257CDBR provides active undershoot protection down to −2 V on both A and B ports. This is achieved via integrated clamp circuitry that senses negative transients and maintains switch OFF-state integrity, preventing false conduction during hot-plug events or ESD-induced excursions. The specification is verified per test conditions in the datasheet (VCC = 5.5 V, switch OFF).

Does the SN74CBT3257CDBR support level shifting between different logic families?

Yes, the SN74CBT3257CDBR supports true bidirectional level shifting across 0.8 V, 1.2 V, 1.5 V, 1.8 V, 2.5 V, 3.3 V, and 5 V domains. Its 0–5.5 V data I/O voltage range and lack of internal level translation circuitry allow it to pass signals transparently between mismatched voltage rails - for example, connecting a 1.8 V FPGA I/O to a 3.3 V microcontroller peripheral without external components.

How does the Ioff feature function in the SN74CBT3257CDBR during partial power-down?

The Ioff feature in the SN74CBT3257CDBR disables all internal conduction paths when VCC = 0 V, limiting leakage current to ≤10 µA even with up to 5.5 V applied to any I/O pin. This prevents back-current flow between powered and unpowered system sections - critical for modular systems, hot-swap backplanes, or battery-backed subsystems where isolated power domains coexist.

What is the thermal performance of the SN74CBT3257CDBR in its SSOP-16 (DB) package?

The SN74CBT3257CDBR in SSOP-16 (DB) package has a junction-to-ambient thermal resistance (θJA) of 82°C/W under standard JEDEC test conditions. This value, confirmed in the Absolute Maximum Ratings table, supports continuous operation at full load within the −40°C to +85°C ambient range when mounted on a 2-layer PCB with recommended copper pour and stencil-defined solder mask openings per TI's DB0016A layout guidelines.

Can the SN74CBT3257CDBR be used in analog signal paths, and what limits its bandwidth?

Yes, the SN74CBT3257CDBR is qualified for analog signal routing due to its low 3 Ω typical ON-state resistance, low 16.5 pF ON-state capacitance (Cio(ON)), and flat ron vs. voltage profile. Bandwidth is primarily limited by the RC time constant formed by ron and load capacitance; with 50 pF load, the −3 dB point exceeds 1 GHz. Signal integrity is further preserved by symmetric FET topology and absence of body diode conduction in analog mode.