Texas Instruments SN74CBT3125CDBR

Overview

SN74CBT3125CDBR from Texas Instruments is a quad 1-bit FET bus switch IC 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 signaling levels across mixed-voltage digital systems such as USB interface isolation.

For engineers reviewing the SN74CBT3125CDBR datasheet, SN74CBT3125CDBR pinout, SN74CBT3125CDBR application, or SN74CBT3125CDBR equivalent, key selection criteria include I_off-enabled partial-power-down operation, 5 pF typical OFF-state I/O capacitance, and SSOP-14 package compatibility with legacy board layouts requiring low-distortion signal gating.

Technical Context

This device implements four independent TTL-compatible FET switches, each controlled by a dedicated OE input (1OE–4OE). When OE is low, the A–B path conducts bidirectionally with near-zero RC delay; when high, the switch enters high-impedance isolation with I_off limiting backflow current during power-down sequences.

The integrated undershoot-protection circuitry actively clamps A/B port voltages down to −2 V while maintaining OFF-state integrity, and data I/Os tolerate 0–5.5 V signals regardless of V_CC level-enabling interoperability between 1.8 V, 2.5 V, 3.3 V, and 5 V logic domains without level shifters.

Key Specifications

Pinout & Package

SN74CBT3125CDBR uses the SSOP-14 (DB) package: 5.9 mm × 4.4 mm body, 0.65 mm lead pitch, 2.0 mm max height, JEDEC MO-150 compliant.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74CBTD3384CDBR and 74LVC1G3157GW,125, the SN74CBT3125CDBR uniquely combines quad-channel density, −2 V undershoot protection, and validated I_off behavior-making it optimal for USB isolation and mixed-voltage bus segmentation where reliability under transient conditions is critical.

Availability

SN74CBT3125CDBR is available at Aetrix Electronics and suitable for USB interface isolation, legacy bus segmentation, and low-distortion signal gating requiring stable component supply across industrial temperature ranges (−40°C to 85°C).

Supply support for SN74CBT3125CDBR 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-reliability IC design.

The SN74CBT3125CDBR belongs to TI's CBT (Crossbar Bus Transceiver) family, engineered for ultra-low-latency, low-distortion signal routing in mixed-voltage digital systems requiring robust hot-plug and power-sequence resilience.

FAQ

What is the maximum undershoot voltage the SN74CBT3125CDBR can withstand on its A/B ports?

The SN74CBT3125CDBR provides active undershoot protection down to −2 V on all A and B port terminals, verified per test conditions in the SCDS122A datasheet. This clamping function remains active even when the switch is disabled (OE = high), ensuring receiver safety during hot-plug events or ESD transients without requiring external diodes. The SN74CBT3125CDBR achieves this via integrated sensing circuitry that forces the switch into a secure OFF state during undershoot.

Does the SN74CBT3125CDBR support partial-power-down operation, and how is it implemented?

Yes, the SN74CBT3125CDBR supports partial-power-down via its I_off feature, specified at 10 µA maximum when V_CC = 0 V and I/O voltages range from 0 to 5.5 V. This guarantees that no damaging backflow current occurs through the device during power-down sequences, enabling safe isolation in multi-rail systems. The SN74CBT3125CDBR maintains high-impedance isolation across all four channels under these conditions, as confirmed in the absolute maximum ratings and electrical characteristics tables.

Can the SN74CBT3125CDBR interface between 1.8 V and 5 V logic domains without external level shifters?

Yes, the SN74CBT3125CDBR supports 0–5.5 V signaling on all A/B I/O ports regardless of V_CC level (4–5.5 V), enabling direct bidirectional interfacing between 1.8 V, 2.5 V, 3.3 V, and 5 V logic families. Its voltage-agnostic architecture eliminates the need for direction-control signals or external translators. The SN74CBT3125CDBR achieves this using FET-based switching with threshold-independent conduction, validated across all recommended operating conditions in the datasheet.

What is the typical ON-state resistance of the SN74CBT3125CDBR, and how does it affect signal integrity?

The SN74CBT3125CDBR has a typical ON-state resistance (r_on) of 3 Ω at V_CC = 4.5 V and I_O = 30 mA, with a maximum of 6 Ω across temperature and voltage extremes. This low r_on minimizes voltage drop and insertion loss-critical for preserving signal amplitude and edge rate in high-speed digital paths. The SN74CBT3125CDBR's r_on consistency ensures predictable timing behavior in applications like USB 1.1 isolation and bus gating where signal fidelity is essential.

Is the SN74CBT3125CDBR pin-compatible with other packages in the same family, such as SN74CBT3125CDR?

No, the SN74CBT3125CDBR (SSOP-14) is not pin-compatible with SN74CBT3125CDR (SOIC-14) despite identical functionality and pin numbering-mechanical dimensions, lead pitch (0.65 mm vs. 1.27 mm), and thermal pad requirements differ significantly. While both share the same 14-pin functional assignment, PCB layout must be redesigned for SSOP due to tighter spacing and different land patterns. The SN74CBT3125CDBR requires adherence to JEDEC MO-150 footprint guidelines, not SOIC MS-012.