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Texas Instruments SN74CBT6845CDW
- Part No.:
- SN74CBT6845CDW
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74CBT6845CDW.pdf
- Description:
- IC BUS SWITCH 8 X 1:1 20SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:40,175
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Product details
Overview
SN74CBT6845CDW from Texas Instruments is an 8-bit 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 live-insertion noise suppression via BIASV-biased B-port precharge. It enables PCI hot-plug–compliant bus isolation in mixed-voltage systems supporting 0.8-V to 5-V signaling.
For engineers reviewing the SN74CBT6845CDW datasheet, SN74CBT6845CDW pinout, SN74CBT6845CDW application, or SN74CBT6845CDW equivalent, key selection criteria include undershoot protection to −2 V on A/B ports, Ioff partial-power-down capability, 5.5 pF typical OFF-state I/O capacitance, and SOIC-DW package compatibility with legacy PCB layouts.
Technical Context
The SN74CBT6845CDW implements eight independent FET transmission gates controlled by a single OE input, enabling simultaneous ON/OFF switching of all channels. Its internal undershoot-protection circuitry actively monitors A and B port voltages and forces the switch into high-impedance state when −2 V undershoot is detected.
B-port terminals are precharged to an externally supplied BIASV voltage (0–VCC) through an internal ~10-kΩ path during OE high or VCC = 0 V, minimizing signal distortion during live insertion. The device supports full 0–5.5 V I/O voltage range independent of VCC, with control inputs compatible with TTL and 3.3/5-V CMOS logic levels.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| ON-state resistance (ron) | 3 Ω typical - ensures minimal voltage drop and signal attenuation across switched paths at ≤64 mA per channel. |
| Propagation delay (tpd) | 0.15 ns typical at VCC = 5 V - enables high-speed, low-latency data gating without timing budget impact. |
| I/O capacitance (Cio(OFF)) | 5.5 pF typical - reduces capacitive loading on buses, preserving signal integrity and edge rates in high-frequency applications. |
| VCC operating range | 4 V to 5.5 V - supports stable operation across industrial-grade 5-V supply tolerances and brownout conditions. |
| Undershoot protection limit | −2 V on A/B ports - prevents false switching and latch-up during connector mating events in hot-plug systems. |
| BIASV voltage range | 0 V to VCC - allows user-selectable precharge level matching receiver input thresholds (e.g., 2.4 V for 3.3-V LVTTL). |
| Ioff current | 10 µA maximum at VCC = 0 V - blocks backflow current during partial power-down, protecting powered subsystems. |
| Supply current (ICC) | 3 µA maximum - enables ultra-low static power in always-on isolation or standby modes. |
Pinout & Package
SN74CBT6845CDW uses a 20-pin SOIC (DW) package with 0.300-inch body width, 1.27 mm pitch, and standard JEDEC MS-013AC outline. Pin 1 is located at the top-left corner with notch or bevel marking.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (OE) | Output enable input | Active-low control: drives all 8 switches ON when low; places B ports in BIASV precharge mode when high. |
| 2–9 (A1–A8) | A-side data I/O | One terminal of each FET switch; connects bidirectionally to corresponding B port when OE = L. |
| 10 (GND) | Ground reference | Primary return path for VCC, BIASV, and signal currents; must be low-impedance for noise immunity. |
| 11 (VCC) | Power supply | Supplies internal bias and switch control logic; range 4–5.5 V; powers undershoot protection circuitry. |
| 12–19 (B1–B8) | B-side data I/O | Second terminal of each FET switch; precharged to BIASV when OE = H or VCC = 0 V. |
| 20 (BIASV) | Bias voltage input | User-supplied voltage (0–VCC) setting precharge level for B ports to suppress live-insertion glitches. |
Key Features
| Feature | Design Value |
|---|---|
| Live-insertion noise suppression | BIASV-controlled B-port precharge eliminates input-threshold crossing during card mating, reducing system-level glitches. |
| PCI Hot Plug compliance | Integrated undershoot protection (−2 V), Ioff, and BIASV precharge meet PCI SIG hot-plug electrical requirements. |
| Mixed-voltage interface support | 0–5.5 V I/O voltage range independent of VCC enables seamless bridging between 0.8-V, 1.2-V, 1.5-V, 1.8-V, 2.5-V, 3.3-V, and 5-V domains. |
| Partial-power-down robustness | Ioff limits reverse current to ≤10 µA when VCC = 0 V, preventing damage to active upstream/downstream circuitry. |
| Low-distortion signal gating | 3 Ω ron and 5.5 pF Cio(OFF) maintain signal fidelity across DC to >500 MHz, critical for memory interleaving and bus arbitration. |
Applications
| PCI Express Slot Isolation | Memory Interleaving Interface |
|---|---|
|
Use Scenario: Hot-plugging PCIe add-in cards into powered-backplane systems without disrupting host CPU or memory controller operation. IC Role / Device Role / Timing Role: Bidirectional bus switch isolating PCIe configuration space and sideband signals during insertion/removal; provides undershoot clamping and BIASV precharge. Use Value: Eliminates bus contention and false command execution caused by live-insertion transients, ensuring reliable enumeration and link training. |
Use Scenario: Dynamically routing address/data lines between dual-channel DDR3 memory controllers and shared DIMM slots. IC Role / Device Role / Timing Role: Low-latency, low-capacitance 8-bit switch enabling real-time memory channel selection without skew or reflection. Use Value: Maintains tight tAC/tDQSS timing margins (<0.15 ns added delay) while supporting 1.5-V DDR3 signaling levels and 5.5 pF load minimization. |
| Industrial Backplane Bus Isolation | Legacy ISA-to-Modern MCU Bridge |
|
Use Scenario: Segregating noisy motor-control I/O modules from sensitive analog acquisition subsystems on shared 5-V backplanes. IC Role / Device Role / Timing Role: High-impedance isolation gate activated only during data transfer windows; suppresses ground bounce and crosstalk coupling. Use Value: Achieves >60 dB noise rejection at 100 MHz via 3 Ω ron matching and 5.5 pF Cio(OFF), preserving 16-bit ADC accuracy. |
Use Scenario: Adapting vintage ISA-bus peripherals (5-V TTL) to modern 3.3-V or 1.8-V microcontroller GPIOs without level-shifter complexity. IC Role / Device Role / Timing Role: Voltage-agnostic bidirectional switch translating between 5-V ISA data/address lines and low-voltage MCU pins. Use Value: Supports full 0–5.5 V I/O swing without external biasing, enabling direct connection to 0.8-V/1.2-V/1.5-V/1.8-V/2.5-V/3.3-V/5-V logic families. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar bus switch applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74CBTD6800CDW | Includes integrated 25-Ω series termination resistors on all A/B I/Os; higher ron (5 Ω typical); same SOIC-DW package. | Better suited for high-speed parallel buses requiring source termination (e.g., SCSI, older video interfaces); adds 25 Ω series impedance. | Select SN74CBTD6800CDW when trace impedance matching and EMI reduction are prioritized over minimal propagation delay. |
| SN74LVC8T245RHLR | 8-bit dual-supply level translator (1.65–5.5 V on A side, 1.65–5.5 V on B side); no BIASV or undershoot protection; 20-pin VQFN (RGY) only. | Designed for voltage translation, not hot-plug isolation; lacks live-insertion features and Ioff; requires two supply rails. | Choose SN74LVC8T245RHLR only for pure level-shifting needs where BIASV precharge and −2 V undershoot clamping are unnecessary. |
Compared with SN74CBT6845CDW, SN74CBTD6800CDW trades 2.5 ns higher propagation delay for built-in termination, while SN74LVC8T245RHLR offers flexible dual-rail translation but omits hot-plug safeguards and SOIC packaging - making SN74CBT6845CDW uniquely suited for PCI-compliant, low-distortion, single-supply bus isolation.
Availability
SN74CBT6845CDW is available at Aetrix Electronics and suitable for PCI interface design, memory interleaving architectures, and industrial bus isolation applications requiring stable component supply, long-term lifecycle support, and SOIC-DW footprint compatibility.
Supply support for SN74CBT6845CDW 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 ICs and industrial-grade solutions.
The SN74CBT6845CDW belongs to TI's CBT (CrossBar Technology) bus switch family, engineered specifically for hot-plug–enabled systems requiring robust signal integrity, low-latency data gating, and mixed-voltage interoperability in computing and industrial infrastructure.
FAQ
What is the maximum undershoot voltage the SN74CBT6845CDW can withstand on its A and B ports?
The SN74CBT6845CDW 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 protection operates independently of VCC and remains effective during live insertion events, ensuring the switch stays in the OFF state when transient undershoot occurs. The SN74CBT6845CDW achieves this via dedicated sensing circuitry that detects sub-ground excursions and disables conduction paths before damage or false switching can occur.
How does the BIASV pin function in the SN74CBT6845CDW during hot-plug operations?
The BIASV pin on the SN74CBT6845CDW supplies a user-defined bias voltage (0 V to VCC) that precharges the B-port I/Os through an internal ~10-kΩ resistor when OE is high or VCC = 0 V. During hot-plug insertion, this precharge holds B-port nodes near the input threshold of downstream receivers (e.g., 2.4 V for 3.3-V LVTTL), preventing transient-induced threshold crossings and eliminating live-insertion noise. The SN74CBT6845CDW relies on this feature to meet PCI Hot Plug specifications without external components.
Can the SN74CBT6845CDW operate with different supply and I/O voltage levels simultaneously?
Yes, the SN74CBT6845CDW supports 0–5.5 V signaling on all data I/Os (A1–A8, B1–B8) regardless of VCC, which operates strictly from 4 V to 5.5 V. This allows interfacing between disparate logic families - such as 1.8-V FPGA I/Os and 5-V microcontrollers - without level shifters. Control inputs (OE) accept TTL or 3.3/5-V CMOS levels. The SN74CBT6845CDW maintains full functionality across this range, validated in the recommended operating conditions table.
What is the role of Ioff in the SN74CBT6845CDW, and how does it protect system-level designs?
Ioff in the SN74CBT6845CDW limits reverse current to ≤10 µA when VCC = 0 V, preventing damaging backflow from powered I/O lines into a powered-down device. This enables safe partial-power-down operation in modular systems - for example, when a peripheral card is removed while the backplane remains active. The SN74CBT6845CDW achieves this via internal transistor cutoff mechanisms that isolate VCC from I/O paths, satisfying JESD78 Class II latch-up immunity and ensuring robust fault containment.
Is the SN74CBT6845CDW pin-compatible with other packages in the same family, such as RGY or PW?
No, the SN74CBT6845CDW (SOIC-DW) is not pin-compatible with SN74CBT6845CRGYR (VQFN-RGY) or SN74CBT6845CPWR (TSSOP-PW), despite identical functionality and pin count. The DW package has a 0.300-inch body width and 1.27 mm pitch, while RGY uses a 3.5 × 4.5 mm QFN layout with exposed thermal pad, and PW follows TSSOP dimensions. Pin numbering differs across packages - for example, BIASV is pin 20 in DW but pin 1 in RGY - so PCB redesign is required for substitution. The SN74CBT6845CDW must be used with its designated SOIC footprint.
SN74CBT6845CDW Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74CBT
- Package/Case:
- 20-SOIC (0.295", 7.50mm Width)
- Packaging:
- Tube
- Product Status:
- Obsolete
- Type:
- Bus Switch
- Circuit:
- 8 x 1:1
- Independent Circuits:
- 1
- Current - Output High, Low:
- -
- Voltage Supply Source:
- Single Supply
- Voltage - Supply:
- 4.5V ~ 5.5V
- Operating Temperature:
- -40°C ~ 85°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-SOIC
SN74CBT6845CDW FAQ
1.How can I place an order for SN74CBT6845CDW through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74CBT6845CDW on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for SN74CBT6845CDW reliable?
The price and inventory of SN74CBT6845CDW are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74CBT6845CDW is usually 5 days.
3.What payment methods are accepted for SN74CBT6845CDW?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74CBT6845CDW transactions.
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4.How is shipping managed for SN74CBT6845CDW?
SN74CBT6845CDW orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74CBT6845CDW order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for SN74CBT6845CDW?
For technical support, including SN74CBT6845CDW datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74CBT6845CDW requirements.
6.How does Aetrix verify that SN74CBT6845CDW is sourced from the original manufacturer or authorized distributors?
All SN74CBT6845CDW products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that SN74CBT6845CDW meets industry standards.
7.What is the process for return or replacement of SN74CBT6845CDW?
All SN74CBT6845CDW units undergo pre-shipment inspection (PSI). If there is an issue with SN74CBT6845CDW, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The SN74CBT6845CDW part is unused and in its original packaging.
Return procedure for SN74CBT6845CDW:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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