Texas Instruments SN74CBT6845CPW

Overview

SN74CBT6845CPW 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 BIASV for live-insertion noise reduction in PCI hot-plug systems.

For engineers reviewing the SN74CBT6845CPW datasheet, SN74CBT6845CPW pinout, SN74CBT6845CPW application, or SN74CBT6845CPW 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 TSSOP-20 package compatibility with hot-swap and bus-isolation designs.

Technical Context

This device implements eight independent FET transmission gates controlled by a single OE input, enabling or disabling bidirectional signal paths between A and B ports. Its internal undershoot-protection circuitry actively holds the switch OFF during −2 V transients, while the BIASV bias voltage (0 to VCC) precharges B-port outputs through an effective 10-kΩ path when OE is high or VCC = 0 V.

The SN74CBT6845CPW supports mixed-voltage signaling (0.8 V to 5 V) on data I/Os and accepts TTL/3.3 V/5 V CMOS logic levels on control inputs. Its Ioff specification ensures backflow current blocking during partial power-down, and latch-up immunity exceeds 100 mA per JESD 78 Class II.

Key Specifications

Pinout & Package

TSSOP-20 package (PW), 6.5 mm × 4.4 mm × 1.2 mm body, 0.65 mm pitch, exposed pad not present, RoHS-compliant NiPdAu finish, MSL Level-1.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74CBT6845CPW, SN74CBTD6800CPW adds level-shifting but removes BIASV-based live-insertion control, while SN74CB3Q3245PW improves ron and speed at the cost of undershoot robustness and mixed-voltage flexibility - making SN74CBT6845CPW uniquely suited for PCI-compliant hot-swap isolation.

Availability

SN74CBT6845CPW is available at Aetrix Electronics and suitable for PCI hot-plug interfaces, memory interleaving architectures, and hot-swappable backplane isolation requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for SN74CBT6845CPW 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 with emphasis on reliability, longevity, and industrial-grade performance.

The SN74CBT6845CPW belongs to TI's CBT (Crossbar Bus Transceiver) family, engineered specifically for high-speed, low-distortion bus isolation in hot-plug-capable systems such as PCI, CompactPCI, and modular computing platforms.

FAQ

What is the maximum undershoot voltage the SN74CBT6845CPW can withstand on its A and B ports?

The SN74CBT6845CPW 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 protection ensures the switch remains reliably OFF during negative transients, preventing unintended conduction. The SN74CBT6845CPW achieves this via internal sensing circuitry that overrides normal switching behavior during undershoot events.

How does the BIASV pin function in the SN74CBT6845CPW during hot-plug events?

The BIASV pin on the SN74CBT6845CPW supplies a user-defined bias voltage (0 V to VCC) that precharges the B-port outputs through an internal ~10-kΩ path when OE is high or VCC = 0 V. During hot-plug, this precharge holds B-port signals near the receiver's input threshold, preventing them from crossing the switching region and causing glitches. This behavior is explicitly documented in the SN74CBT6845CPW datasheet's live-insertion noise reduction section.

Does the SN74CBT6845CPW support partial-power-down operation, and how is it implemented?

Yes, the SN74CBT6845CPW supports partial-power-down operation via its Ioff feature. When VCC = 0 V, the device limits Ioff to 10 µA maximum across the full VI/O range (0–5.5 V), blocking damaging backflow current from live buses into unpowered circuitry. This capability is verified in the electrical characteristics table and enables safe isolation in modular systems where subsystems may be powered independently - a core design requirement of the SN74CBT6845CPW.

What is the typical ON-state resistance (ron) of the SN74CBT6845CPW, and under what conditions is it measured?

The typical ON-state resistance (ron) of the SN74CBT6845CPW is 3 Ω, measured at VCC = 4.5 V, VI = 0 V, and IO = 30 mA, as specified in the electrical characteristics table. This value reflects the resistance between A and B terminals when the switch is enabled (OE low), directly impacting voltage drop and signal integrity. The SN74CBT6845CPW maintains this low ron across its 4–5.5 V VCC range, supporting high-fidelity signal routing in demanding applications.

Can the SN74CBT6845CPW interface between different logic voltage domains, and what are its I/O voltage limits?

Yes, the SN74CBT6845CPW supports 0–5.5 V signaling on its A and B data I/Os, enabling interoperability across 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 or 3.3-V/5-V CMOS levels, and VI/O absolute maximum rating is −0.5 V to 7 V. This wide voltage tolerance is intrinsic to the SN74CBT6845CPW's FET-switch architecture and is validated across recommended operating conditions.