SN74CBT6845CPWR

Overview

The SN74CBT6845CPWR is an 8-bit FET bus switch manufactured by Texas Instruments, housed in a 20-pin TSSOP package. It operates within a supply voltage range of 4 V to 5.5 V and supports data I/O levels from 0 V to 5.5 V. The device features low ON-state resistance (ron) with typical values of 3 Ω at 4.5 V and 8 Ω at 4 V. Propagation delay is specified as 0.15 ns at 5 V and 0.24 ns at 4 V. It includes active undershoot protection up to -2 V on A and B ports, precharged B-port outputs via the BIASV pin, and Ioff support for partial-power-down isolation.

Feature Summary

• Active undershoot-protection circuitry on A and B ports ensures proper OFF state during undershoot events up to -2 V.
• B port outputs are precharged to a user-selectable bias voltage (BIASV) to minimize signal distortion during live insertion and hot-plugging.
• Supports partial-power-down mode operation using Ioff feature to prevent damaging backflow current when powered down.
• Bidirectional data flow with near-zero propagation delay and low input/output capacitance to minimize loading effects.

Applications

• PCI interface applications requiring hot-plug support
• Memory interleaving systems
• Bus isolation circuits
• Low-distortion signal gating

Procurement Notes

Verify the ordering suffix 'R' indicates tape-and-reel packaging containing 2000 units per large reel. Confirm the package drawing corresponds to the PW (TSSOP-20) outline. Ensure the operating temperature range matches the application requirements of -40°C to +85°C. Check for RoHS compliance status and lead finish specifications in the latest package addendum.

Selection Notes

Select this component when designing high-speed bidirectional bus switches requiring low propagation delay and minimal signal distortion. The device is suitable for applications needing active undershoot protection and precharged outputs to handle live-insertion scenarios. Ensure control inputs are driven by TTL or 5-V/3.3-V CMOS outputs to meet VIH/VIL specifications.

Part Context

The SN74CBT6845C series belongs to Texas Instruments' high-speed TTL-compatible FET bus switch family. This specific part number represents the tape-and-reel variant of the SN74CBT6845CPW. It shares functional characteristics with other members of the SN74CBT6845C family but differs in packaging and shipping configuration.

Replacement Considerations

SN74CBT6845CPW is the tube-packaged equivalent of the same functional device. SN74CBT6845CRGYR offers identical functionality in a VQFN package. Verify pinout compatibility and thermal performance when substituting between package types.

FAQ

How does the device handle live insertion noise?

The B port is precharged to the BIASV voltage through an equivalent 10-kΩ resistor when OE is high or during power-down. This minimizes glitching on the active bus during card insertion or removal.

What is the function of the Ioff feature?

The Ioff feature ensures that damaging current will not backflow through the device when it is powered down (VCC = 0 V), providing isolation during partial-power-down applications.

Can the control inputs be driven by 3.3-V logic?

Yes, the control inputs can be driven by TTL or 5-V/3.3-V CMOS outputs, provided the VIH and VIL specifications are met.