Texas Instruments SN74CBT3125CDBQR

Overview

SN74CBT3125CDBQR 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 mixed-voltage signaling (0.8 V to 5 V) in USB interface and bus isolation applications.

For engineers reviewing the SN74CBT3125CDBQR datasheet, SN74CBT3125CDBQR pinout, SN74CBT3125CDBQR application, or SN74CBT3125CDBQR equivalent, key selection criteria include Ioff partial-power-down capability, 5 pF OFF-state I/O capacitance, TTL/CMOS-compatible control inputs, and SSOP-16 package thermal performance (θJA = 90°C/W).

Technical Context

This device implements four independent single-pole single-throw (SPST) analog switches using NMOS pass transistors with integrated undershoot-protection circuitry. Each switch features active clamping that maintains OFF-state isolation when A or B port voltage drops to −2 V, preventing false turn-on during signal transients.

Control logic uses active-low OE inputs (1OE–4OE) to enable/disable individual switches; low OE connects A↔B bidirectionally, high OE places ports in high-impedance state. The Ioff specification ensures no backflow current when VCC = 0 V, enabling safe partial-power-down operation in multi-rail systems.

Key Specifications

Pinout & Package

SN74CBT3125CDBQR is housed in a 16-pin Shrink Small-Outline Package (SSOP-DBQ), 5.8 mm × 4.0 mm body, 0.65 mm lead pitch, 1.75 mm max height, moisture sensitivity level 2 (260°C peak reflow).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74CBT3125CDBQR, SN74CBTD3384CDBQR offers greater channel count but sacrifices undershoot robustness, while TS3A24159RGTR delivers lower resistance at the cost of 5-V compatibility and transient protection-making SN74CBT3125CDBQR optimal for industrial USB and mixed-voltage bus isolation.

Availability

SN74CBT3125CDBQR is available at Aetrix Electronics and suitable for USB interface design, industrial bus isolation, low-distortion analog multiplexing, and FPGA I/O voltage translation requiring stable component supply across extended temperature ranges (−40°C to 85°C).

Supply support for SN74CBT3125CDBQR 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 delivering analog, embedded processing, and connectivity solutions for industrial, automotive, and communications markets.

The SN74CBT3125CDBQR belongs to TI's CBT (Crosspoint Bus Transceiver) family, engineered for high-speed, low-distortion signal routing in mixed-voltage digital systems with stringent transient immunity requirements.

FAQ

What is the maximum undershoot voltage the SN74CBT3125CDBQR can withstand on its A and B ports?

The SN74CBT3125CDBQR provides active undershoot protection up to −2 V on both A and B ports. This is achieved via internal clamping circuitry that senses negative transients and forces the switch into a reliable OFF state, preventing unintended conduction or latch-up. The specification is verified per test conditions in the datasheet (VCC = 5.5 V, switch OFF, VIN = VCC or GND), and applies directly to the SN74CBT3125CDBQR in its DBQ package.

Does the SN74CBT3125CDBQR support bidirectional signal flow without direction control pins?

Yes, the SN74CBT3125CDBQR supports fully bidirectional signal flow between each A and B port pair without requiring direction control. Each of the four 1-bit switches operates as a passive analog path: when enabled (OE low), signals pass with equal impedance and delay in either direction. This eliminates timing skew and simplifies PCB layout compared to directional buffers. The SN74CBT3125CDBQR achieves this using symmetrical NMOS pass-gate topology with matched threshold characteristics.

What is the thermal performance of the SN74CBT3125CDBQR in its SSOP-16 (DBQ) package?

The SN74CBT3125CDBQR in the SSOP-16 (DBQ) package has a specified junction-to-ambient thermal resistance (θJA) of 90°C/W under standard JEDEC test conditions. This value enables reliable operation at full rated load across the −40°C to 85°C ambient range when mounted on a 2-layer PCB with typical copper pour. The DBQ package's 0.65 mm lead pitch and 1.75 mm height are optimized for thermal dissipation in space-constrained industrial modules, and the SN74CBT3125CDBQR's low ICC (3 µA max) further minimizes self-heating.

Can the SN74CBT3125CDBQR interface between 1.8-V and 5-V logic domains?

Yes, the SN74CBT3125CDBQR supports seamless interfacing between 1.8-V and 5-V logic domains. Its data I/Os tolerate 0–5.5 V regardless of VCC setting (4–5.5 V), and its control inputs accept TTL/CMOS levels-including 1.8-V logic-high signals (VIH min = 2 V). When VCC = 5 V, the SN74CBT3125CDBQR passes 1.8-V signals with minimal attenuation due to its 3 Ω ron and 5 pF Cio(OFF), making it ideal for bridging FPGA I/O banks to legacy 5-V peripherals without external level shifters.

How does the Ioff feature of the SN74CBT3125CDBQR protect system-level power sequencing?

The Ioff feature of the SN74CBT3125CDBQR limits current to 10 µA when VCC = 0 V and I/O voltages range from 0–5.5 V, preventing damaging back-current flow between powered and unpowered subsystems. During power-down sequences-such as hot-plug events or partial system resets-the SN74CBT3125CDBQR maintains isolation even if A or B ports remain energized, eliminating risk of latch-up or supply rail contamination. This behavior is characterized and guaranteed across temperature, distinguishing the SN74CBT3125CDBQR from standard bus switches lacking Ioff.