Texas Instruments SN74CBT6845CDGVR

Overview

SN74CBT6845CDGVR from Texas Instruments is an 8-bit high-speed TTL-compatible FET bus switch with bidirectional data flow, 3 Ω typical ON-state resistance (ron), −2 V undershoot protection on A/B ports, and B-port precharge via user-selectable BIASV for live-insertion noise suppression in PCI hot-plug systems.

For engineers reviewing the SN74CBT6845CDGVR datasheet, SN74CBT6845CDGVR pinout, SN74CBT6845CDGVR application, or SN74CBT6845CDGVR equivalent, key selection criteria include its 0.15 ns propagation delay at 5 V, 5.5 pF OFF-state I/O capacitance, Ioff partial-power-down support, 4–5.5 V VCC operation, and compatibility with 0.8–5 V signaling levels across mixed-voltage buses.

Technical Context

The SN74CBT6845CDGVR implements eight independent FET transmission gates controlled by a single OE input, enabling simultaneous ON/OFF switching of all A↔B paths. Its internal undershoot-protection circuitry actively monitors A and B port voltages and forces the switch into OFF state when −2 V undershoot is detected.

B-port terminals are precharged to BIASV through an internal ~10-kΩ equivalent resistor during OE HIGH or VCC = 0 V, minimizing signal distortion during hot-plug events. The device supports true bidirectional signal flow with near-zero RC-delay propagation (0.15 ns typical at 5 V) and maintains high-impedance isolation between ports when disabled.

Key Specifications

Pinout & Package

SN74CBT6845CDGVR uses the TVSOP (DGV) package: 20-pin, 4.4 mm × 6.5 mm body, 0.65 mm pitch, 1.2 mm max height, with exposed thermal pad for enhanced thermal dissipation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74CBT6845CDGVR, SN74CBTD6800PWR offers more channels but lacks critical hot-plug features and voltage flexibility, while PI3CH485LE provides simpler biasing at the expense of design adaptability and robustness in live-insertion scenarios.

Availability

SN74CBT6845CDGVR is available at Aetrix Electronics and suitable for PCI hot-plug interfaces, memory interleaving architectures, and mixed-voltage FPGA bridging requiring stable component supply, long-term lifecycle assurance, and RoHS-compliant packaging.

Supply support for SN74CBT6845CDGVR 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 and industrial-grade reliability.

The SN74CBT6845CDGVR belongs to TI's CBT (Crosspoint Bus Transceiver) family, engineered specifically for low-distortion, high-bandwidth signal gating in hot-pluggable computing and communications infrastructure.

FAQ

What is the maximum undershoot voltage the SN74CBT6845CDGVR can withstand on its A and B ports?

The SN74CBT6845CDGVR provides active undershoot protection up to −2 V on both A and B ports, as verified in the absolute maximum ratings and functional testing per SCDS140. This protection operates independently of VCC and remains active even during partial power-down, ensuring reliable isolation when cards are inserted into live backplanes. The SN74CBT6845CDGVR achieves this via internal sensing circuitry that forces the switch into OFF state during undershoot events.

How does the BIASV pin function in the SN74CBT6845CDGVR during hot-plug operations?

The BIASV pin on the SN74CBT6845CDGVR supplies a user-defined voltage (0 V to VCC) that precharges the B-port terminals through an internal ~10-kΩ equivalent resistor when OE is HIGH or VCC = 0 V. This precharge holds B1–B8 near the receiver's input threshold-such as 1.2 V for PCIe-so that connector parasitic capacitance during insertion does not drive the signal across the switching region. The SN74CBT6845CDGVR thus minimizes live-insertion noise without external components.

Can the SN74CBT6845CDGVR operate with a 3.3-V supply voltage?

No, the SN74CBT6845CDGVR requires a minimum VCC of 4 V per its recommended operating conditions; it is not rated for 3.3-V operation. Attempting to power the SN74CBT6845CDGVR at 3.3 V may result in undefined switching behavior, increased ron, or failure to meet undershoot protection specifications. For 3.3-V systems, TI recommends alternatives like SN74CBTD6800PWR-but note those lack BIASV and −2 V undershoot capability.

What is the typical ON-state resistance (ron) of the SN74CBT6845CDGVR and how does it affect signal integrity?

The SN74CBT6845CDGVR has a typical ON-state resistance of 3 Ω at VCC = 4.5 V, measured under 30 mA load. This low ron ensures minimal voltage drop (<90 mV at 30 mA) and preserves signal amplitude across 8-bit parallel buses, directly supporting clean edge transitions and reduced timing skew. Because ron is matched across all eight channels, the SN74CBT6845CDGVR maintains consistent propagation delay and avoids data-dependent jitter in high-speed memory or address routing applications.

Does the SN74CBT6845CDGVR support partial-power-down mode, and how is it implemented?

Yes, the SN74CBT6845CDGVR fully supports partial-power-down mode via its Ioff specification: leakage current is limited to 10 µA maximum when VCC = 0 V and I/O voltages range from 0 to 5.5 V. This feature prevents damaging backflow current from powered sections into unpowered ones-critical in modular systems where one board may be removed while others remain active. The SN74CBT6845CDGVR achieves this through internal transistor cutoff design, validated per JESD 78 Class II latch-up standards.