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Texas Instruments SN74AS651DW
- Part No.:
- SN74AS651DW
- Manufacturer:
- Texas Instruments
- Package:
- -
- Datasheet:
-
SN74AS651DW.pdf
- Description:
- REGISTERED BUS TRANSCEIVER
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Inventory:1,176
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Product details
Overview
SN74AS651DW from Texas Instruments is an octal bus transceiver and register with 3-state outputs, inverting data path, and dual independent clock/control logic for A↔B bidirectional data routing. It supports real-time or stored data transfer, operates at up to 90 MHz clock frequency, delivers 48 mA low-level output drive, and is housed in a 24-pin SOIC (DW) package for industrial bus interface applications.
For engineers reviewing the SN74AS651DW datasheet, SN74AS651DW pinout, SN74AS651DW application, or SN74AS651DW equivalent, this device is selected for high-speed bidirectional bus isolation, register-controlled data staging, and mixed-mode timing-critical systems requiring simultaneous A/B bus control with glitch-free select transitions.
Technical Context
The SN74AS651DW integrates eight D-type flip-flops with separate CLKAB/CLKBA inputs, enabling independent latching of data from either bus. Its SAB/SBA select controls eliminate multiplexer decoding glitches by ensuring deterministic transition between real-time and stored data paths - a low level selects real-time transfer, high level selects stored data.
Output-enable logic (OEAB/OEBA) provides per-bus 3-state control, while the inverting data path ensures signal polarity consistency across A→B and B→A transfers. All I/O ports support TTL-compatible voltage thresholds (VIH = 2 V, VIL = 0.8 V) and operate over 0°C to 70°C with 4.5–5.5 V supply.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Function | Octal inverting bus transceiver with dual-register storage and 3-state outputs |
| Max Clock Frequency | 90 MHz - enables high-throughput data staging in fast parallel buses |
| IOL (Low-Level Output) | 48 mA - drives heavy capacitive loads or multiple TTL inputs without external buffers |
| VCC Range | 4.5 V to 5.5 V - compatible with standard 5 V logic rails and tolerant of supply ripple |
| Propagation Delay (tPLH/tPHL) | 6–10 ns (CLK→A/B), 2–18 ns (A/B→A/B) - supports sub-10 ns timing budgets in synchronous designs |
| Operating Temperature | 0°C to 70°C - qualified for commercial-grade embedded and industrial control systems |
| Package | 24-pin SOIC (DW) - surface-mount footprint with 46°C/W thermal resistance for board-level power dissipation |
Pinout & Package
SN74AS651DW uses a 24-pin SOIC (DW) package with standard pinout per TI SDAS066G Rev. December 2000. Pin numbering follows top-view orientation with pin 1 at bottom-left corner.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | CLKBA | Clock input for latching data from Bus A into internal register for Bus B output |
| 2 | SBA | Select control: low = real-time A→B transfer, high = stored A→B transfer |
| 3 | OEBA | Output enable for Bus B outputs driving Bus A - active-low 3-state control |
| 4–11 | A1–A8 | Bus A data I/O terminals - bidirectional, inverting path to B bus |
| 12 | GND | Ground reference for all logic and I/O circuits |
| 13 | VCC | Positive supply (4.5–5.5 V) for core logic and output drivers |
| 14–21 | B1–B8 | Bus B data I/O terminals - bidirectional, inverting path to A bus |
| 22 | OEAB | Output enable for Bus A outputs driving Bus B - active-low 3-state control |
| 23 | SAB | Select control: low = real-time B→A transfer, high = stored B→A transfer |
| 24 | CLKAB | Clock input for latching data from Bus B into internal register for Bus A output |
Key Features
| Feature | Design Value |
|---|---|
| Inverting Data Path | Ensures consistent signal inversion across both A→B and B→A directions, simplifying level alignment in legacy TTL systems |
| Glitch-Free Select Control | SAB/SBA logic prevents metastability during mode switching between real-time and stored data paths |
| Dual Independent Clocks | CLKAB and CLKBA allow asynchronous latching of A and B bus data without shared timing constraints |
| 48 mA Output Drive | Supports direct interfacing to multiple TTL loads or high-capacitance backplanes without fanout buffers |
| 3-State Output Enables | Separate OEAB and OEBA pins provide granular bus arbitration and prevent contention during multi-master operation |
Applications
| Industrial Backplane Interface | Legacy System Bus Extension |
|---|---|
Use Scenario: Interfacing a microprocessor local bus to a distributed I/O backplane with timing-critical read/write cycles. IC Role / Device Role / Timing Role: SN74AS651DW acts as a bidirectional, register-staged bus transceiver - isolating CPU address/data lines from noisy backplane traces while enabling synchronized data capture. Use Value: 90 MHz clock capability and 48 mA drive ensure reliable data transfer across 12-inch PCB traces with >30 pF load, eliminating need for repeater ICs. | Use Scenario: Extending a vintage 8-bit ISA-style bus to add new peripheral slots while preserving original timing and voltage compatibility. IC Role / Device Role / Timing Role: SN74AS651DW serves as a drop-in replacement for obsolete 74LS651, providing identical pinout and inverting logic with improved speed and drive strength. Use Value: Inverting path matches legacy bus polarity; 2–10 ns propagation delays meet strict ISA setup/hold timing windows without redesigning control logic. |
| Test Equipment Data Acquisition | Programmable Logic Controller (PLC) I/O Module |
Use Scenario: Capturing parallel sensor data streams in automated test equipment where real-time sampling and buffered logging must coexist. IC Role / Device Role / Timing Role: SN74AS651DW routes raw sensor inputs (Bus B) to ADC interface (Bus A) in real-time, while simultaneously storing snapshots in internal registers for post-trigger analysis. Use Value: Dual-clock architecture allows concurrent real-time pass-through and register capture on same data edge - no added latency or external latch required. | Use Scenario: Isolating field I/O signals from PLC CPU bus under EMI-prone factory floor conditions with frequent hot-swap events. IC Role / Device Role / Timing Role: SN74AS651DW functions as a controlled bus barrier - OEAB/OEBA enable/disable A/B ports independently during module insertion/removal to prevent bus contention. Use Value: 3-state control with <12 ns disable time ensures zero glitch on CPU bus during hot-swap; 46°C/W θJA supports continuous operation at 70°C ambient. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal bus transceiver and register applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS651A-DW | ALS family: lower speed (40 MHz max), lower IOL (24 mA), higher VIH (2.0 V), same pinout and function | Lower power consumption but insufficient for >50 MHz or high-fanout loads | Select when system clock ≤40 MHz and drive requirements ≤24 mA; not suitable for SN74AS651DW's 90 MHz or 48 mA use cases |
| SN74AS652DW | True (non-inverting) data path; otherwise identical timing, drive, and pinout | Required where signal polarity must be preserved end-to-end (e.g., memory bus extensions) | Choose SN74AS652DW only when inverting behavior is incompatible with downstream logic; otherwise SN74AS651DW maintains functional equivalence with polarity correction |
Compared with SN74ALS651A-DW, SN74AS651DW delivers 2.25× higher clock rate and double the output current - critical for modernizing legacy bus interfaces. Against SN74AS652DW, it provides identical performance with inverted logic, making it the sole choice for systems requiring polarity inversion in bidirectional data flow.
Availability
SN74AS651DW is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy system bus extensions, test equipment data acquisition, and programmable logic controller I/O modules requiring stable component supply across long production lifecycles.
Supply support for SN74AS651DW 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 logic solutions with decades of legacy logic product support.
The SN74AS651DW belongs to TI's advanced Schottky (AS) logic family, designed specifically for high-speed, high-drive parallel bus applications in industrial, test, and computing infrastructure where reliability and pin-compatible upgrade paths matter.
FAQ
What is the maximum clock frequency supported by the SN74AS651DW?
The SN74AS651DW supports a maximum clock frequency of 90 MHz under recommended operating conditions (VCC = 4.5 V to 5.5 V, TA = 0°C to 70°C). This rating applies to both CLKAB and CLKBA inputs and is validated per TI SDAS066G Rev. December 2000. The 90 MHz capability enables high-throughput data staging in fast parallel bus architectures where SN74AS651DW is deployed.
Does the SN74AS651DW have an inverting or non-inverting data path?
The SN74AS651DW features an inverting data path - meaning data transferred from Bus A to Bus B, or Bus B to Bus A, undergoes logical inversion. This is confirmed in the device description table of SDAS066G, which explicitly lists 'AS651 as "Inverting". The inverting behavior is inherent to the SN74AS651DW silicon design and affects all bidirectional data transfers through its internal logic.
What are the key differences between SN74AS651DW and SN74ALS651A-DW?
SN74AS651DW offers 90 MHz max clock frequency and 48 mA low-level output drive, whereas SN74ALS651A-DW is limited to 40 MHz and 24 mA. Both share identical 24-pin SOIC (DW) packaging and pinout, but SN74AS651DW uses advanced Schottky technology for superior speed and drive. SN74AS651DW is not a drop-in replacement for SN74ALS651A-DW in timing-critical or high-current applications without validation.
Can SN74AS651DW operate with a 3.3 V supply?
No, SN74AS651DW is specified only for 4.5 V to 5.5 V supply operation per its recommended operating conditions in SDAS066G. It is not 3.3 V compatible - applying 3.3 V will result in undefined logic levels, degraded noise margins, and failure to meet timing or drive specifications. For 3.3 V systems, designers must use level-shifting circuitry or select a 3.3 V–compatible transceiver family instead of SN74AS651DW.
How does the select-control logic (SAB/SBA) prevent glitches during mode switching on SN74AS651DW?
The SN74AS651DW implements dedicated select-control circuitry that eliminates typical multiplexer decoding glitches during transitions between real-time and stored data modes. When SAB or SBA changes state, internal synchronization ensures the output remains valid throughout the transition - no intermediate invalid states occur. This behavior is documented in the functional description of SDAS066G and verified in timing diagrams, making SN74AS651DW suitable for glitch-sensitive bus arbitration scenarios.
SN74AS651DW Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- *
- Package/Case:
- -
- Packaging:
- Bulk
- Product Status:
- Active
- Logic Type:
- -
- Number of Elements:
- -
- Number of Bits per Element:
- -
- Input Type:
- -
- Output Type:
- -
- Current - Output High, Low:
- -
- Voltage - Supply:
- -
- Operating Temperature:
- -
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- -
- Supplier Device Package:
- -
SN74AS651DW FAQ
1.How can I place an order for SN74AS651DW through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74AS651DW 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 SN74AS651DW reliable?
The price and inventory of SN74AS651DW are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74AS651DW is usually 5 days.
3.What payment methods are accepted for SN74AS651DW?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74AS651DW transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74AS651DW?
SN74AS651DW orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74AS651DW 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 SN74AS651DW?
For technical support, including SN74AS651DW datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74AS651DW requirements.
6.How does Aetrix verify that SN74AS651DW is sourced from the original manufacturer or authorized distributors?
All SN74AS651DW 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 SN74AS651DW meets industry standards.
7.What is the process for return or replacement of SN74AS651DW?
All SN74AS651DW units undergo pre-shipment inspection (PSI). If there is an issue with SN74AS651DW, 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 SN74AS651DW part is unused and in its original packaging.
Return procedure for SN74AS651DW:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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