Texas Instruments SN74CBT6845CDBR

Overview

SN74CBT6845CDBR 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 SN74CBT6845CDBR datasheet, SN74CBT6845CDBR pinout, SN74CBT6845CDBR application, or SN74CBT6845CDBR equivalent, key selection criteria include Ioff partial-power-down support, 0–5-V signal level compatibility across 0.8 V to 5 V logic families, and 0.15 ns typical propagation delay at 5 V.

Technical Context

This device implements eight independent FET-based analog/digital switches controlled by a single OE input. Each switch features active undershoot-protection circuitry that maintains OFF-state integrity when A/B port voltages dip to −2 V, and internal 10-kΩ-equivalent biasing to BIASV on the B port during power-down or OE-high states.

The architecture supports true bidirectional signal gating with near-zero RC-limited propagation delay (0.15 ns typ. at VCC = 5 V), low 5.5 pF typical OFF-state I/O capacitance, and full isolation under Ioff conditions-enabling safe operation in partially powered systems without backflow current.

Key Specifications

Pinout & Package

SN74CBT6845CDBR is housed in a 20-pin SSOP (Shrink Small Outline Package) with 0.65 mm pitch, 7.2 mm × 5.3 mm body size, and exposed thermal pad not present - suitable for standard reflow assembly and board-level thermal management without heatsinking.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74CBT6845CDBR, SN74CBTD6800DBR offers greater channel count but sacrifices hot-plug readiness and voltage flexibility, while SN74CB3Q3245PWR delivers finer threshold control at the cost of added external components and reduced undershoot resilience.

Availability

SN74CBT6845CDBR is available at Aetrix Electronics and suitable for PCI hot-plug interface design, memory interleaving bus isolation, and mixed-voltage logic translation requiring stable component supply, long-term lifecycle assurance, and RoHS-compliant packaging.

Supply support for SN74CBT6845CDBR 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 SN74CBT6845CDBR belongs to TI's CBT (Crossbar Bus Transceiver) family, engineered specifically for high-speed, low-distortion signal gating in hot-plug-capable computing and communications infrastructure.

FAQ

What is the maximum undershoot voltage the SN74CBT6845CDBR can withstand on its A and B ports?

The SN74CBT6845CDBR provides active undershoot protection up to −2 V on both A and B ports, as verified in the absolute maximum ratings and functional description. This capability ensures the switch remains reliably OFF during live-insertion transients, preventing unintended conduction and bus corruption. The protection circuitry senses undershoot events independently on each port and maintains isolation without external components. SN74CBT6845CDBR achieves this within its specified 4 V to 5.5 V VCC range and does not require additional clamping diodes.

How does the BIASV pin function in the SN74CBT6845CDBR during hot-plug operations?

The BIASV pin on the SN74CBT6845CDBR sets the precharge voltage for all eight B-port terminals when OE is high or VCC = 0. During hot-plug insertion, this precharge-typically set to match the input threshold of downstream receivers-minimizes voltage glitches by preventing the B port from being pulled toward GND by parasitic capacitance. SN74CBT6845CDBR implements this via an internal ~10-kΩ-equivalent path, eliminating the need for external resistors. BIASV must be maintained between 0 V and VCC for correct operation.

Does the SN74CBT6845CDBR support partial-power-down mode, and how is it implemented?

Yes, the SN74CBT6845CDBR fully supports partial-power-down mode via its Ioff feature. When VCC = 0 V, the device limits backflow current to ≤10 µA regardless of voltage applied to A or B ports, ensuring isolation and preventing damage to powered circuitry. This behavior is characterized per JESD 78 Class II latch-up testing and confirmed in electrical specifications. SN74CBT6845CDBR achieves this through internal transistor cutoff mechanisms-not external enable logic-making it suitable for systems with staggered power sequencing.

What is the typical ON-state resistance (ron) of the SN74CBT6845CDBR, and how does it affect signal integrity?

The SN74CBT6845CDBR has a typical ON-state resistance (ron) 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 power dissipation during signal transmission, preserving amplitude and edge fidelity-especially critical for analog signals and high-speed digital buses. SN74CBT6845CDBR maintains this performance bidirectionally and across its full 0–5.5 V I/O voltage range, supporting clean pass-through of signals up to ±128 mA per channel.

Can the SN74CBT6845CDBR be used for level translation between different logic families, and which voltage levels are supported?

Yes, the SN74CBT6845CDBR supports bidirectional level translation across 0.8-V, 1.2-V, 1.5-V, 1.8-V, 2.5-V, 3.3-V, and 5-V logic families due to its 0–5.5 V data I/O voltage range and TTL/CMOS-compatible control inputs (VIH ≥ 2 V, VIL ≤ 0.8 V). It requires no direction pin or external biasing. SN74CBT6845CDBR operates with VCC = 4–5.5 V, making it ideal for translating from legacy 5-V sources to modern low-voltage processors while maintaining signal integrity via low 5.5 pF OFF-state capacitance and 3 Ω ron.