Texas Instruments SN74CBT6845CRGYR

Overview

SN74CBT6845CRGYR from Texas Instruments is an 8-bit bidirectional FET bus switch with near-zero propagation delay (0.15 ns typical at 5 V), 3 Ω typical ON-state resistance, and active undershoot protection up to −2 V on both A and B ports. It supports hot-plug operation in PCI systems via B-port precharge to user-selectable BIASV and enables partial-power-down mode via Ioff.

For engineers reviewing the SN74CBT6845CRGYR datasheet, SN74CBT6845CRGYR pinout, SN74CBT6845CRGYR application, or SN74CBT6845CRGYR equivalent, key selection criteria include live-insertion noise suppression, 0–5-V signal level compatibility across 7 logic families, and thermal performance of the 3.5 mm × 4.5 mm VQFN-20 package with 37°C/W θJA.

Technical Context

The SN74CBT6845CRGYR implements TTL-compatible control inputs (OE) driving eight independent transmission-gate switches, each with integrated undershoot-sensing circuitry that forces OFF-state retention during −2 V transients. Its B-port precharge path uses an internal ~10-kΩ equivalent resistor to BIASV, minimizing signal distortion during card insertion into live buses.

It operates from 4 V to 5.5 V VCC while supporting data I/O signaling from 0 V to 5.5 V - including 0.8 V, 1.2 V, 1.5 V, 1.8 V, 2.5 V, 3.3 V, and 5 V logic levels - and features Ioff isolation that prevents backflow current when VCC = 0 V, meeting JESD 78 Class II latch-up requirements (>100 mA).

Key Specifications

Pinout & Package

VQFN-20 package (RGY), 3.5 mm × 4.5 mm body, 0.5 mm pitch, exposed thermal pad, 1 mm max height. Pin 1 index located at top-left corner with quadrant Q1 orientation per tape-and-reel specification.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74CBT6845CRGYR, SN74CBTD6800PWR offers more channels but sacrifices live-insertion readiness, while SN74LVC2G66DCUR trades speed, protection, and precharge capability for compact size and wider VCC range - making SN74CBT6845CRGYR uniquely suited for PCI-compliant hot-plug isolation.

Availability

SN74CBT6845CRGYR is available at Aetrix Electronics and suitable for PCI interface design, memory interleaving architectures, and industrial bus isolation applications requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for SN74CBT6845CRGYR 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-reliability interface solutions.

The SN74CBT6845CRGYR belongs to TI's CBT (Crossbar Bus Transceiver) family, engineered specifically for high-speed, low-distortion bus switching in hot-plug-capable computing and communications infrastructure.

FAQ

What is the maximum undershoot voltage the SN74CBT6845CRGYR can withstand on its A and B ports?

The SN74CBT6845CRGYR provides active undershoot protection up to −2 V on both A and B ports, as confirmed in the absolute maximum ratings and functional description. This ensures the switch remains reliably OFF during live-insertion events where transient negative spikes occur. The protection circuit senses undershoot and enforces proper isolation, preventing false conduction that could disrupt the host bus. This rating applies across the full operating temperature range (−40°C to 85°C) and is validated per JESD 22 test methods.

How does the BIASV pin function in the SN74CBT6845CRGYR, and what voltage range is supported?

The BIASV pin on the SN74CBT6845CRGYR supplies a user-selectable bias voltage to precharge the B-port outputs when OE is high or VCC = 0 V. It accepts voltages from 0 V to VCC (4 V to 5.5 V), enabling precise alignment with downstream receiver input thresholds - typically set near 1.2 V or 1.5 V for PCI systems. This precharge, implemented via an internal ~10-kΩ equivalent resistor, suppresses live-insertion noise by preventing B-port signals from crossing receiver switching thresholds during card mating. BIASV is a supply, not a control input, and must be decoupled locally.

Is the SN74CBT6845CRGYR compatible with 1.8-V or 2.5-V logic systems?

Yes, the SN74CBT6845CRGYR supports 0–5.5 V data I/O signaling, explicitly listing compatibility with 0.8-V, 1.2-V, 1.5-V, 1.8-V, 2.5-V, 3.3-V, and 5-V logic families. Its control inputs accept TTL- and CMOS-level signals, and its low 5.5 pF Cio(OFF) and 3 Ω ron minimize loading and voltage drop across these voltage domains. This makes SN74CBT6845CRGYR suitable for mixed-voltage board designs without external level shifters, provided VCC is maintained within 4–5.5 V and BIASV is configured appropriately for the target receiver threshold.

What thermal performance can be expected from the SN74CBT6845CRGYR in its RGY package?

The SN74CBT6845CRGYR in the VQFN-20 RGY package has a specified junction-to-ambient thermal resistance (θJA) of 37°C/W under standard JEDEC PCB conditions (2S2P, 1-inch² copper). This value reflects the benefit of its exposed thermal pad, which must be soldered to a PCB thermal plane for optimal performance. At 3 µA ICC and typical switching loads, self-heating remains negligible; however, under sustained 128 mA per channel, thermal design must account for pad layout, via count, and board copper area to maintain junction temperature below 125°C. Thermal data is validated per JESD 51-5.

Does the SN74CBT6845CRGYR support partial-power-down operation, and how is it implemented?

Yes, the SN74CBT6845CRGYR fully supports partial-power-down via its Ioff feature. When VCC = 0 V, the device limits off-state current to ≤10 µA even with up to 5.5 V applied to I/O pins, preventing damaging backflow through powered-down sections of the system. This behavior is guaranteed over temperature and is integral to the switch architecture - no external circuitry is required. Ioff compliance exceeds JESD 78 Class II latch-up requirements (>100 mA), ensuring robustness during power sequencing in complex embedded systems using SN74CBT6845CRGYR for bus segmentation.