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Texas Instruments SN74ACT3651-20PCB
- Part No.:
- SN74ACT3651-20PCB
- Manufacturer:
- Texas Instruments
- Category:
- FIFOs Memory
- Package:
- 120-LQFP
- Datasheet:
-
SN74ACT3651-20PCB.pdf
- Description:
- IC FIFO SYNC 2KX36 120HLQFP
- Quantity:
- Payment:
- Shipping:
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Product details
Overview
SN74ACT3651-20PCB from Texas Instruments is a 2048 × 36-bit clocked FIFO memory IC with dual asynchronous ports (A and B), supporting up to 67 MHz clock frequencies, 11 ns read access time, and synchronous retransmit capability. It implements mailbox registers, programmable almost-full/almost-empty flags, and microprocessor interface logic for high-throughput data buffering between dissimilar clock domains in telecom and DSP systems.
For engineers reviewing the SN74ACT3651-20PCB datasheet, SN74ACT3651-20PCB pinout, SN74ACT3651-20PCB application, or SN74ACT3651-20PCB equivalent, key selection criteria include dual-port SRAM depth/width, CLKA/CLKB synchronization behavior, flag latency (two-stage sync), retransmit mode timing, and PCB-package pin compatibility with SN74ACT3631/SN74ACT3641.
Technical Context
The SN74ACT3651-20PCB employs a 2048 × 36-bit dual-port SRAM core with independent free-running CLKA and CLKB clocks that may be asynchronous or coincident. Its retransmit logic uses shadow and current read pointers to enable repeat reads from a user-selected starting address without disrupting ongoing writes.
Status flags (IR, OR, AF, AE) are two-stage synchronized to their respective port clocks-IR and AF to CLKA, OR and AE to CLKB-reducing metastability risk. Flag offsets (X for AE, Y for AF) are programmable via preset (8 or 64), parallel load from Port A, or 22-bit serial load through FS0/SD and FS1/SEN.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Memory Depth × Width | 2048 × 36 bits - supports 73.7 kbit buffered data transfer between independent clock domains |
| Max Clock Frequency | 67 MHz - enables real-time streaming in high-speed serial interfaces and packet buffers |
| Read Access Time | 11 ns - guarantees sub-15 ns latency from CLKB edge to valid output data on B0–B35 |
| Flag Synchronization | Two-stage flip-flop sync - ensures reliable flag assertion under asynchronous CLKA/CLKB operation |
| Operating Temperature | 0°C to 70°C - qualified for commercial-grade embedded systems and industrial control backplanes |
| Technology Node | 0.8-µm Advanced CMOS - delivers low power consumption with TTL-compatible input thresholds |
| Retransmit Capability | Synchronous retransmit mode - allows repeat reads from arbitrary FIFO address without pointer reset or data loss |
Pinout & Package
The SN74ACT3651-20PCB is housed in a 120-pin Thin Quad Flat Package (TQFP), designated "PCB" in TI documentation, with 0.4 mm lead pitch and exposed thermal pad. Pin numbering follows standard TQFP top-view convention.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| A0–A35, B0–B35 | Dual 36-bit bidirectional data buses | Port-A and Port-B I/O paths; high-impedance when CSA/W/RA or CSB/W/RB inactive |
| CLKA, CLKB | Free-running port clocks | Independent synchronous timing references; IR/AF synced to CLKA, OR/AE synced to CLKB |
| ENA, ENB | Port master enables | Gate all port operations; must be high for CLKA/CLKB edges to trigger read/write |
| CSA, CSB | Chip select inputs | Enable port activity only when low; place data bus in high-Z when deasserted |
| W/RA, W/RB | Port write/read direction controls | W/RA high = write to Port A; W/RB high = read from Port B (inverted logic) |
| IR, OR, AF, AE | Synchronized status flags | IR/AF tied to CLKA domain; OR/AE tied to CLKB domain; used for handshaking and flow control |
| MBA, MBB | Mailbox register selectors | Select mail1/mail2 bypass registers instead of FIFO core for command/control transfers |
| RST | Asynchronous reset input | Requires four CLKA + four CLKB rising edges low-to-high while RST held low |
| RTM, RFM | Retransmit control signals | RTM initiates retransmit mode; RFM triggers re-read from marked location during RTM |
| FS0/SD, FS1/SEN | Flag offset programming interface | Configure AE/AF thresholds via serial load (22-bit), preset (8 or 64), or parallel load from Port A |
Key Features
| Feature | Design Value |
|---|---|
| Synchronous retransmit mode | Enables repeat reads from any FIFO address using shadow read pointer-critical for FIR filter coefficient replay and DMA restart scenarios |
| Programmable almost-empty/almost-full flags | AE/AF thresholds set via 22-bit serial, 11-bit parallel, or fixed presets-enables adaptive buffer management in variable-rate systems |
| Dual 36-bit mailbox registers | Mail1 (Port A → Port B) and Mail2 (Port B → Port A) provide non-blocking command channel alongside main FIFO path |
| Two-stage flag synchronization | IR/AF and OR/AE each pass through two flip-flops clocked by CLKA/CLKB-eliminates metastability-induced handshake failures |
| Pin-to-pin compatibility | Direct replacement for SN74ACT3631 and SN74ACT3641-enables drop-in upgrade path with no PCB change |
Applications
| Telecom Line Card Buffering | DSP Coefficient Streaming |
|---|---|
Use Scenario: Interfacing TDM framer ICs running at 8 kHz frame rate with high-speed serial processors operating at 67 MHz. IC Role / Device Role / Timing Role: Clocked FIFO bridging mismatched clock domains while maintaining deterministic latency and preventing overflow/underflow. Use Value: Eliminates need for complex clock-domain-crossing logic; 2048-word depth absorbs bursty traffic; programmable AF/AE enables dynamic backpressure signaling. | Use Scenario: Streaming FIR filter coefficients from host processor memory to a fixed-point DSP executing at 50 MHz. IC Role / Device Role / Timing Role: Dual-port FIFO with retransmit mode serving as coefficient replay buffer for multi-tap filtering operations. Use Value: Synchronous retransmit allows repeated coefficient reads without CPU intervention; mailbox registers handle control commands independently of data flow. |
| Industrial PLC Data Aggregation | Network Packet Assembly |
Use Scenario: Consolidating sensor data from multiple 100 kHz sampling modules into a single Ethernet controller with variable transmit intervals. IC Role / Device Role / Timing Role: High-bandwidth FIFO with programmable almost-empty flag triggering DMA fetches before buffer depletion. Use Value: 11 ns access time ensures minimal jitter in time-critical I/O cycles; two-stage flag sync prevents spurious interrupts during clock domain transitions. | Use Scenario: Assembling fragmented Ethernet frames from multiple ingress ports before forwarding to switch fabric. IC Role / Device Role / Timing Role: Dual-port FIFO acting as elastic store between ingress arbitration logic (Port A) and egress scheduler (Port B). Use Value: Independent CLKA/CLKB clocks accommodate different port timing; mailbox registers carry frame metadata (length, priority) alongside payload. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar clocked FIFO applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ACT3631-20PCB | Same 120-pin PCB package, identical pinout, but 1024 × 36 capacity and no retransmit mode | Lacks synchronous retransmit and mailbox registers; suitable only for basic buffering without replay or sideband control | Choose when cost sensitivity outweighs need for retransmit or mailbox functionality |
| SN74ACT3641-20PCB | Same 120-pin PCB package and pinout; 2048 × 36 depth but no retransmit mode or mailbox registers | Provides full depth and flag programmability but omits retransmit logic and dual-mailbox architecture | Select when maximum buffer depth is required without coefficient replay or command-channel isolation |
Compared with SN74ACT3631-20PCB and SN74ACT3641-20PCB, the SN74ACT3651-20PCB uniquely integrates retransmit capability and dual mailbox registers-enabling advanced DSP workflows and concurrent control/data paths without external logic or software overhead.
Availability
SN74ACT3651-20PCB is available at Aetrix Electronics and suitable for telecom line cards, DSP-based signal processing units, industrial PLC data concentrators, and network packet assembly engines requiring stable component supply across extended production lifecycles.
Supply support for SN74ACT3651-20PCB 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 over 50 years of innovation in high-reliability timing and interface ICs.
The SN74ACT3651-20PCB belongs to TI's ACT-family clocked FIFO product line, designed specifically for deterministic, low-latency data buffering across asynchronous clock domains in communications infrastructure and real-time digital signal processing systems.
FAQ
What is the maximum supported clock frequency for SN74ACT3651-20PCB?
The SN74ACT3651-20PCB supports clock frequencies up to 67 MHz on both CLKA and CLKB inputs. This specification is guaranteed across the full commercial temperature range (0°C to 70°C) and reflects the device's optimized 0.8-µm Advanced CMOS process. Operation beyond this limit may result in timing violations or metastability in flag outputs.
How does the retransmit mode function in SN74ACT3651-20PCB?
The SN74ACT3651-20PCB enters retransmit mode (RTM) when RTM is high and OR is high, capturing the current FIFO output register content as the first retransmit word. Subsequent reads cycle through FIFO contents starting from that point. The RFM signal allows restarting the retransmit sequence from the marked location without exiting RTM, enabling repeat coefficient loading or test pattern replay.
What are the flag synchronization requirements for SN74ACT3651-20PCB?
The SN74ACT3651-20PCB synchronizes IR and AF flags to CLKA using two flip-flop stages, and OR and AE flags to CLKB using the same dual-stage method. This design reduces metastability probability when CLKA and CLKB operate asynchronously. Each flag requires two clock cycles to reflect state changes-e.g., AE updates two CLKB edges after a write affecting fill level.
Can SN74ACT3651-20PCB be used with different clock frequencies on CLKA and CLKB?
Yes-the SN74ACT3651-20PCB explicitly supports asynchronous CLKA and CLKB operation, including independent frequencies up to 67 MHz each. Its two-stage synchronized flags (IR/AF to CLKA, OR/AE to CLKB) and separate read/write pointer logic ensure robust handshaking across clock domains without external synchronizers.
What package type does SN74ACT3651-20PCB use, and is it pin-compatible with other variants?
The SN74ACT3651-20PCB uses a 120-pin Thin Quad Flat Package (TQFP) designated "PCB" by Texas Instruments. It is pin-to-pin compatible with SN74ACT3631-20PCB and SN74ACT3641-20PCB, sharing identical footprint, pin count, and signal mapping-allowing direct substitution in existing PCB layouts without redesign.
SN74ACT3651-20PCB Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ACT
- Package/Case:
- 120-LQFP
- 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:
- 120-HLQFP (14x14)
SN74ACT3651-20PCB FAQ
1.How can I place an order for SN74ACT3651-20PCB through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ACT3651-20PCB 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 SN74ACT3651-20PCB reliable?
The price and inventory of SN74ACT3651-20PCB are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ACT3651-20PCB is usually 5 days.
3.What payment methods are accepted for SN74ACT3651-20PCB?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ACT3651-20PCB transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ACT3651-20PCB?
SN74ACT3651-20PCB orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ACT3651-20PCB 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 SN74ACT3651-20PCB?
For technical support, including SN74ACT3651-20PCB datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ACT3651-20PCB requirements.
6.How does Aetrix verify that SN74ACT3651-20PCB is sourced from the original manufacturer or authorized distributors?
All SN74ACT3651-20PCB 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 SN74ACT3651-20PCB meets industry standards.
7.What is the process for return or replacement of SN74ACT3651-20PCB?
All SN74ACT3651-20PCB units undergo pre-shipment inspection (PSI). If there is an issue with SN74ACT3651-20PCB, 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 SN74ACT3651-20PCB part is unused and in its original packaging.
Return procedure for SN74ACT3651-20PCB:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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