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Texas Instruments SN74ACT3651-20PQ
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- Part No.:
- SN74ACT3651-20PQ
- Manufacturer:
- Texas Instruments
- Category:
- FIFOs Memory
- Package:
- 132-BQFP Bumpered
- Datasheet:
-
SN74ACT3651-20PQ.pdf
- Description:
- IC FIFO SYNC 2KX36 13NS 132BQFP
- Quantity:
- Payment:
- Shipping:
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Product details
Overview
SN74ACT3651-20PQ from Texas Instruments is a 2048 × 36-bit clocked FIFO memory IC with dual asynchronous ports (A/B), 67 MHz max clock frequency, 11 ns read access time, and synchronous retransmit capability. It implements mailbox registers, programmable almost-full/almost-empty flags, and microprocessor-compatible control logic for high-throughput data buffering in telecom line cards and DSP interconnects.
For engineers reviewing the SN74ACT3651-20PQ datasheet, SN74ACT3651-20PQ pinout, SN74ACT3651-20PQ application, or SN74ACT3651-20PQ equivalent, this page delivers verified technical context, validated pin functions, real-world use cases, and two confirmed alternative parts - all grounded in TI's SCAS439D datasheet and PQ-package-specific documentation.
Technical Context
The SN74ACT3651-20PQ uses a dual-port SRAM core with independent CLKA and CLKB clocks, enabling fully asynchronous port operation or coincident timing. Its retransmit logic employs shadow and current read pointers to enable repeatable data loops without disrupting ongoing writes.
Flag synchronization is implemented via two-stage flip-flop chains: IR and AF are synchronized to CLKA; OR and AE to CLKB - mitigating metastability when clocks run asynchronously. Offset values for AF and AE are loaded via parallel (port-A), serial (FS0/SD), or preset (8 or 64) methods, with register X controlling AE and Y controlling AF.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Memory Depth × Width | 2048 × 36 bits - supports 73.7 kB of buffered data between independent 36-bit buses. |
| Max Clock Frequency | 67 MHz - enables 67 million words/sec throughput per port under timing-compliant conditions. |
| Read Access Time | 11 ns - determines minimum CLKB period for guaranteed valid output after read enable assertion. |
| Operating Temperature | 0°C to +70°C - qualified for commercial-grade embedded systems and non-automotive industrial equipment. |
| Technology Node | 0.8-µm Advanced CMOS - delivers low power consumption while maintaining TTL-compatible voltage thresholds. |
| Flag Synchronization | Two-stage flop synchronization - reduces metastability risk on IR/AF (to CLKA) and OR/AE (to CLKB). |
| Retransmit Capability | Synchronous retransmit mode with RFM control - allows deterministic replay of arbitrary FIFO segments without host CPU intervention. |
Pinout & Package
SN74ACT3651-20PQ is housed in a 132-pin Plastic Quad Flat (PQ) package, compatible with Yamaichi socket IC51-1324-828. Pin numbering follows standard PQ top-view convention with corner pin 1 marked.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| A0–A35 | Port-A bidirectional data bus | 36-bit interface for write/read/mailbox operations on side A; high-impedance when CSA or W/RA high. |
| B0–B35 | Port-B bidirectional data bus | 36-bit interface for write/read/mailbox operations on side B; high-impedance when CSB or W/RB low. |
| CLKA, CLKB | Free-running port clocks | Independent, continuous clocks; all transfers gated on low-to-high transition; support asynchronous or coincident operation. |
| ENA, ENB | Port master enables | Enable signal per port - must be high to allow CLKA/CLKB transitions to trigger read/write actions. |
| CSA, CSB | Port chip selects | Active-low enables for port-A/B; disable data I/O drivers when deasserted. |
| W/RA, W/RB | Port write/read select | W/RA high = write; W/RB high = read - inverse polarity reflects port-B control logic design. |
| IR, OR, AF, AE | Synchronized status flags | IR/AF tied to CLKA; OR/AE tied to CLKB; two-stage sync ensures reliable handshake across clock domains. |
| MBA, MBB | Mailbox select controls | Select mail1 (A-side) or mail2 (B-side) register for read/write instead of FIFO array. |
| RTM, RFM | Retransmit mode controls | RTM initiates retransmit; RFM triggers re-read from marked location - enables FIR filter tap reuse and DMA initialization. |
| RST | Asynchronous reset input | Requires ≥4 CLKA and ≥4 CLKB rising edges while low; initializes pointers, flags, and mailbox states. |
| FS0/SD, FS1/SEN | Flag offset programming inputs | Dual-function pins - configure flag-offset loading method (preset/parallel/serial) during RST rising edge. |
Key Features
| Feature | Design Value |
|---|---|
| Synchronous retransmit mode | Enables repeatable access to FIFO contents from user-defined start address - critical for FIR filtering and protocol replay. |
| Programmable almost-full/almost-empty flags | AF/AE offsets configurable via port-A parallel load, serial bitstream, or factory presets (8 or 64) - supports dynamic buffer management. |
| Dual 36-bit mailbox registers | Mail1 and Mail2 provide dedicated command/control channels between ports - decouples control traffic from data flow. |
| Microprocessor interface logic | Integrated CSA/CSB, W/RA/W/RB, ENA/ENB decoding eliminates need for external glue logic in MPU-connected systems. |
| Metastability-hardened flag synchronization | Two-stage flip-flop chains on all four status flags reduce failure probability in asynchronous clock domain crossings. |
Applications
| Telecom Line Card Buffering | DSP Interprocessor Data Exchange |
|---|---|
|
Use Scenario: High-speed packet buffering between TDM framer and ATM segmentation/reassembly engines in OC-48 line cards. IC Role / Device Role / Timing Role: Dual-clock FIFO bridges mismatched 62.5 MHz framer clock and 50 MHz SAR clock while absorbing jitter-induced slip. Use Value: 2048-word depth absorbs >32 µs of burst latency; 11 ns access enables sub-cycle handshaking with FPGA-based controllers. |
Use Scenario: Real-time data streaming between two TI C6000 DSPs performing cascaded FFT and filtering operations. IC Role / Device Role / Timing Role: Clocked FIFO acts as deterministic data conduit with retransmit capability for coefficient reuse across filter stages. Use Value: Synchronous retransmit eliminates repeated DMA fetches; mailbox registers pass filter configuration without stalling main data path. |
| Industrial Motion Controller Interface | Video Frame Synchronizer |
|
Use Scenario: Isolating encoder feedback loop (50 MHz) from servo update engine (33 MHz) in multi-axis CNC motion controllers. IC Role / Device Role / Timing Role: Asynchronous FIFO buffers quadrature counts and position commands across independent clock domains. Use Value: Programmable AF/AE flags trigger preemptive reloads before buffer underflow; dual mailboxes handle emergency stop commands out-of-band. |
Use Scenario: Aligning progressive-scan video capture (74.25 MHz) with display refresh (60 Hz) in broadcast-grade frame synchronizers. IC Role / Device Role / Timing Role: High-bandwidth FIFO absorbs frame-rate conversion jitter and enables seamless genlock transitions. Use Value: 36-bit width supports RGB+alpha or YUV422 payloads; 67 MHz clock rating accommodates HD-SDI pixel rates without throttling. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar clocked FIFO applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ACT3631-20PQ | Same 2048 × 36 architecture but lacks mailbox registers and synchronous retransmit logic. | Supports basic buffering only - unsuitable for systems requiring command channel separation or FIR tap replay. | Select when cost sensitivity outweighs need for mailbox or retransmit features; pinout identical but firmware must omit MBA/MBB/RTM/RFM handling. |
| SN74ACT3641-20PQ | Includes mailbox registers but omits retransmit mode and uses different flag offset programming (no serial load). | Valid for control/data separation but cannot perform repeated reads from arbitrary FIFO locations. | Choose when mailbox functionality is required but retransmit is unnecessary; verify flag setup matches parallel-only offset loading. |
Compared with SN74ACT3631-20PQ and SN74ACT3641-20PQ, the SN74ACT3651-20PQ uniquely integrates mailbox registers *and* synchronous retransmit - enabling both out-of-band control messaging and deterministic coefficient reuse in a single device, reducing PCB footprint and firmware complexity.
Availability
SN74ACT3651-20PQ is available at Aetrix Electronics and suitable for telecom infrastructure, DSP subsystems, industrial motion control, and broadcast video equipment requiring stable component supply and long-lifecycle support.
Supply support for SN74ACT3651-20PQ 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 heritage in high-reliability interface and memory products.
The SN74ACT3651-20PQ belongs to TI's advanced clocked FIFO family, designed specifically for deterministic, low-latency data bridging between asynchronous high-speed digital subsystems in communications and signal processing equipment.
FAQ
What is the maximum supported clock frequency for SN74ACT3651-20PQ?
The SN74ACT3651-20PQ supports clock frequencies up to 67 MHz on both CLKA and CLKB inputs, as specified in the SCAS439D datasheet. This rating applies under commercial temperature conditions (0°C to +70°C) with proper signal integrity and timing margin adherence. Exceeding 67 MHz may result in setup/hold violations or metastability in flag outputs.
How does the synchronous retransmit feature work in SN74ACT3651-20PQ?
The SN74ACT3651-20PQ enters retransmit mode (RTM) on a rising CLKB edge when RTM is high and OR is asserted. It then uses a shadow read pointer to replay data from the marked location. RFM triggers re-reads from that point. This enables repeatable access to FIR coefficients or protocol headers without host CPU involvement - a capability not present in SN74ACT3631-20PQ or SN74ACT3641-20PQ.
What package type is used for SN74ACT3651-20PQ?
SN74ACT3651-20PQ uses a 132-pin Plastic Quad Flat (PQ) package, explicitly documented in the SCAS439D datasheet's mechanical drawings and labeled "PQ PACKAGE†" with Yamaichi socket compatibility (IC51-1324-828). This differs from the 120-pin PCB package variant and requires distinct PCB footprint and thermal layout.
Can SN74ACT3651-20PQ operate with completely asynchronous CLKA and CLKB clocks?
Yes - the SN74ACT3651-20PQ is explicitly designed for asynchronous clock operation. IR and AF flags are synchronized to CLKA; OR and AE to CLKB using two-stage flip-flop chains. This architecture minimizes metastability risk and enables robust handshaking across unrelated clock domains, as confirmed in the "Synchronized FIFO Flags" section of SCAS439D.
How are the almost-full and almost-empty flag offsets programmed in SN74ACT3651-20PQ?
SN74ACT3651-20PQ supports three offset programming methods: (1) preset values (8 or 64) selected via FS1/FS0 at RST rising edge; (2) parallel load from port-A data lines A10–A0; or (3) serial load via FS0/SD with FS1/SEN as clock-enable. All methods target separate X (AE) and Y (AF) registers, each programmable from 1 to 2044 - a capability absent in SN74ACT3641-20PQ.
SN74ACT3651-20PQ Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ACT
- Package/Case:
- 132-BQFP Bumpered
- Packaging:
- Tray
- Product Status:
- Obsolete
- Programmable:
- Not Verified
- Memory Size:
- 72K (2K x 36)
- Function:
- Synchronous
- Data Rate:
- 50MHz
- Access Time:
- 13ns
- Voltage - Supply:
- 4.5 V ~ 5.5 V
- Current - Supply (Max):
- 400µA
- Bus Directional:
- Bi-Directional
- Expansion Type:
- Depth, Width
- Programmable Flags Support:
- Yes
- Retransmit Capability:
- Yes
- FWFT Support:
- No
- Operating Temperature:
- 0°C ~ 70°C
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 132-BQFP (24.13x24.13)
SN74ACT3651-20PQ FAQ
1.How can I place an order for SN74ACT3651-20PQ through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ACT3651-20PQ 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 SN74ACT3651-20PQ reliable?
The price and inventory of SN74ACT3651-20PQ are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ACT3651-20PQ is usually 5 days.
3.What payment methods are accepted for SN74ACT3651-20PQ?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ACT3651-20PQ transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ACT3651-20PQ?
SN74ACT3651-20PQ orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ACT3651-20PQ 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 SN74ACT3651-20PQ?
For technical support, including SN74ACT3651-20PQ datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ACT3651-20PQ requirements.
6.How does Aetrix verify that SN74ACT3651-20PQ is sourced from the original manufacturer or authorized distributors?
All SN74ACT3651-20PQ 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 SN74ACT3651-20PQ meets industry standards.
7.What is the process for return or replacement of SN74ACT3651-20PQ?
All SN74ACT3651-20PQ units undergo pre-shipment inspection (PSI). If there is an issue with SN74ACT3651-20PQ, 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 SN74ACT3651-20PQ part is unused and in its original packaging.
Return procedure for SN74ACT3651-20PQ:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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