Texas Instruments SN74CBT6845CDWR

Overview

SN74CBT6845CDWR from Texas Instruments is an 8-bit high-speed TTL-compatible FET bus switch with bidirectional data flow, near-zero propagation delay (0.15 ns typical at 5 V), 3 Ω typical ON-state resistance, and undershoot protection up to −2 V on A/B ports - deployed in PCI hot-plug interfaces and memory interleaving systems.

For engineers reviewing the SN74CBT6845CDWR datasheet, SN74CBT6845CDWR pinout, SN74CBT6845CDWR application, or SN74CBT6845CDWR equivalent, key selection criteria include live-insertion noise suppression via BIASV precharge, Ioff partial-power-down support, 0–5-V signal level compatibility, and SOIC-20 package thermal performance (θJA = 58°C/W).

Technical Context

The SN74CBT6845CDWR implements eight independent FET-based analog switches controlled by a single OE input, enabling or disabling bidirectional conduction between A and B ports. Its internal undershoot-protection circuitry actively holds the switch OFF during −2 V transients, while B-port precharge to user-supplied BIASV (0–VCC) minimizes live-insertion glitches.

It supports partial-power-down via Ioff, blocking backflow current when VCC = 0 V, and features TTL/CMOS-compatible control inputs with 4–5.5 V VCC operation. Data I/Os tolerate 0–5.5 V signals and include clamp diodes for undershoot immunity.

Key Specifications

Pinout & Package

SN74CBT6845CDWR is housed in a 20-pin SOIC (DW) package with 1.27 mm pitch, 7.5 mm × 12.8 mm body, and 58°C/W junction-to-ambient thermal resistance - optimized for through-hole prototyping and automated surface-mount assembly.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74CBT6845CDWR, SN74CBTD6800CDW trades live-insertion robustness for lower cost in static systems, while PI3CH485QEX offers smaller footprint but requires external design effort to replicate BIASV functionality and lacks −2 V undershoot hardening.

Availability

SN74CBT6845CDWR is available at Aetrix Electronics and suitable for PCI hot-plug interfaces, memory interleaving systems, and industrial bus isolation requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for SN74CBT6845CDWR 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 SN74CBT6845CDWR belongs to TI's CBT (Crossbar Bus Transceiver) family, engineered specifically for high-speed, low-distortion bus switching in hot-plug and mixed-voltage system environments.

FAQ

What is the maximum undershoot voltage the SN74CBT6845CDWR can withstand on its A and B ports?

The SN74CBT6845CDWR provides active undershoot protection up to −2 V on both A and B ports, as verified in the absolute maximum ratings and functional test conditions. This protection ensures the switch remains reliably OFF during transient negative excursions, preventing false logic states in hot-plug scenarios. The SN74CBT6845CDWR achieves this via internal sensing circuitry that overrides normal switching behavior when undershoot is detected.

How does the BIASV pin function in the SN74CBT6845CDWR during hot-plug events?

The BIASV pin on the SN74CBT6845CDWR supplies a user-defined bias voltage (0 V to VCC) to precharge the B-port outputs when OE is high or VCC = 0 V. During hot-plug, this precharge holds B lines near the input threshold of downstream receivers (e.g., 1.2 V or 2.4 V), ensuring any transient induced by connector mating stays outside the receiver's switching region. The SN74CBT6845CDWR uses an internal ~10-kΩ equivalent resistor to apply BIASV, eliminating need for external components.

Does the SN74CBT6845CDWR support partial-power-down operation, and how is it implemented?

Yes, the SN74CBT6845CDWR fully supports partial-power-down via its Ioff feature. When VCC = 0 V, the device limits Ioff leakage to 10 µA maximum across all I/Os, preventing damaging backflow current from live buses into the unpowered IC. This behavior is specified over the full VI/O range (0–5.5 V) and enables safe integration into systems where subsystems power up/down independently. The SN74CBT6845CDWR maintains high-impedance isolation even with VCC absent.

What is the typical ON-state resistance (ron) of the SN74CBT6845CDWR, and how does it affect signal integrity?

The SN74CBT6845CDWR has a typical ON-state resistance of 3 Ω at VCC = 4.5 V and IO = 30 mA, with a maximum of 6 Ω across temperature and voltage ranges. This low ron minimizes voltage drop and signal attenuation - for example, a 64 mA signal experiences only ~192 mV drop - preserving logic margins and reducing timing skew. The SN74CBT6845CDWR's ron consistency also ensures uniform channel-to-channel delay, critical for parallel bus applications.

Can the SN74CBT6845CDWR interface between 3.3-V and 5-V logic domains without external level shifters?

Yes, the SN74CBT6845CDWR supports 0–5.5 V signaling on all data I/Os (A1–A8, B1–B8), allowing seamless bidirectional voltage translation between 3.3-V and 5-V domains. Its control inputs (OE) accept TTL or CMOS logic levels, and VCC operates from 4–5.5 V - so a 5-V supply enables direct interfacing with both 3.3-V and 5-V buses. The SN74CBT6845CDWR requires no external components for level shifting, simplifying BOM and layout.