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Texas Instruments SN74ACT3651-20PBC
- Part No.:
- SN74ACT3651-20PBC
- Manufacturer:
- Texas Instruments
- Category:
- FIFOs Memory
- Package:
- -
- Datasheet:
-
SN74ACT3651-20PBC.pdf
- Description:
- IC FIFO 2KX36 11NS
- Quantity:
- Payment:
- Shipping:
Inventory:176
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Product details
Overview
SN74ACT3651-20PBC from Texas Instruments is a 2048 × 36-bit clocked FIFO memory IC with dual asynchronous ports, 67 MHz max clock frequency, 11 ns read access time, and synchronous retransmit capability. It buffers high-speed data between microprocessor buses or DSP interfaces using independent CLKA/CLKB clocks and supports mailbox register communication for control signaling.
For engineers reviewing the SN74ACT3651-20PBC datasheet, SN74ACT3651-20PBC pinout, SN74ACT3651-20PBC application, or SN74ACT3651-20PBC equivalent, key selection criteria include dual-port timing independence, programmable almost-full/empty thresholds, mailbox register flag synchronization, and compatibility with TI's ACT-family FIFO interface standards.
Technical Context
The SN74ACT3651-20PBC implements a 2048-word × 36-bit dual-port SRAM-based FIFO with fully synchronous, clock-gated port A (CLKA) and port B (CLKB) interfaces. Each port uses two-stage synchronized flags (IR/AF on CLKA; OR/AE on CLKB) to mitigate metastability in asynchronous clock domains.
It integrates mailbox registers (Mail1/Mail2) with dedicated MBA/MBB controls and supports three offset programming modes-preset (8 or 64), parallel load via port A, or serial load via FS0/SD-enabling precise buffer-level monitoring for real-time flow control in DSP and communications systems.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Memory Depth × Width | 2048 × 36 bits - provides 73.7 kB of buffered data storage for burst-mode interconnects |
| Max Clock Frequency | 67 MHz - enables 67 Mwords/s throughput per port under optimal timing conditions |
| Read Access Time | 11 ns - guarantees deterministic latency from CLKB edge to valid output data at B0–B35 |
| Flag Synchronization | Two-stage flip-flop sync - ensures reliable IR/AF sampling on CLKA and OR/AE on CLKB across asynchronous domains |
| Operating Temperature | 0°C to +70°C - qualified for commercial-grade embedded systems and industrial control applications |
| Technology Node | 0.8-µm Advanced CMOS - delivers low power consumption while maintaining TTL-compatible voltage levels |
| Programmable Offsets | AE/AF thresholds settable from 1 to 2044 words - allows fine-grained flow control without firmware intervention |
Pinout & Package
SN74ACT3651-20PBC is packaged 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 | Port-A bidirectional data bus | 36-bit parallel interface for write/read operations gated by CLKA, CSA, W/RA, ENA |
| B0–B35 | Port-B bidirectional data bus | 36-bit parallel interface for write/read operations gated by CLKB, CSB, W/RB, ENB |
| CLKA / CLKB | Free-running port clocks | Independent synchronous timing sources; support asynchronous or coincident operation |
| IR / OR / AF / AE | Synchronized status flags | IR/AF tied to CLKA domain; OR/AE tied to CLKB domain; all two-stage synchronized |
| MBA / MBB | Mailbox select inputs | Enable access to Mail1 (port A) or Mail2 (port B); control flag generation (MBF1/MBF2) |
| RTM / RFM | Retransmit control signals | RTM initiates synchronous retransmit mode; RFM triggers re-read from marked location |
| FS0/SD / FS1/SEN | Flag offset programming I/O | Dual-function pins for serial loading of AE/AF offset registers (22-bit sequence) |
| RST | Asynchronous reset input | Requires ≥4 CLKA and ≥4 CLKB rising edges low-to-high while RST held low |
Key Features
| Feature | Design Value |
|---|---|
| Synchronous retransmit mode | Enables repeat reads from user-defined start address without disrupting ongoing writes or pointer advancement |
| Dual mailbox registers | Mail1 and Mail2 provide dedicated 36-bit command/control channels between ports with flag-acknowledged handshaking |
| Programmable almost-full/empty flags | AE/AF thresholds configurable via preset, parallel, or serial methods-eliminates polling overhead in real-time systems |
| Microprocessor interface logic | Integrated CSA/CSB, W/RA/W/RB, ENA/ENB decoding simplifies connection to 80Cxx or 68K-style buses |
| Metastability-hardened flag paths | All status outputs use dual-register synchronization to ensure robust operation across independent clock domains |
Applications
| DSP Data Streaming | FPGA-to-Microprocessor Bridge |
|---|---|
Use Scenario: Real-time FIR filtering where input samples arrive faster than processing rate, requiring temporary buffering before computation. IC Role / Device Role / Timing Role: Clocked FIFO acting as elastic buffer between ADC interface clock domain and DSP core clock domain. Use Value: Synchronous retransmit allows repeated access to filter coefficients stored in FIFO; programmable AF/AE prevents overflow/underflow during variable-load processing cycles. |
Use Scenario: High-bandwidth data transfer between FPGA-accelerated subsystem and legacy microprocessor bus with mismatched timing margins. IC Role / Device Role / Timing Role: Dual-clock FIFO decouples FPGA fabric clock (e.g., 100 MHz) from microprocessor bus clock (e.g., 25 MHz). Use Value: Independent CLKA/CLKB domains eliminate need for complex clock-domain-crossing logic; mailbox registers handle handshake commands without consuming main data path bandwidth. |
| Industrial PLC Communication | Digital Signal Acquisition System |
Use Scenario: Buffering sensor data packets from multiple fieldbus nodes before aggregation and protocol translation in a central controller. IC Role / Device Role / Timing Role: FIFO serves as deterministic latency buffer between time-critical fieldbus interrupt handlers and slower background task scheduler. Use Value: Two-stage synchronized flags (IR/OR) guarantee glitch-free status reporting across clock boundaries; programmable AE threshold triggers early DMA request to avoid data loss. |
Use Scenario: Capturing high-speed analog waveform data from multi-channel digitizers before streaming to host PC via USB or PCIe interface. IC Role / Device Role / Timing Role: Front-end FIFO absorbs burst acquisition rates exceeding sustained host interface throughput. Use Value: 2048-word depth accommodates full waveform capture at 67 MSPS; retransmit mode enables verification replay of critical segments without reacquisition. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar clocked FIFO applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ACT3631-20PBC | Same 120-pin PCB package and pinout; identical 2048 × 36 capacity but lacks mailbox registers and retransmit capability | Suitable only for basic FIFO buffering without sideband control channel or repeat-read functionality | Select when mailbox and retransmit features are unnecessary and cost reduction is prioritized |
| SN74ACT3641-20PBC | Same footprint and clock specs; differs in flag behavior-AF/AE are level-sensitive rather than edge-triggered and lack two-stage sync | Less robust in highly asynchronous multi-clock systems; requires external synchronizers for safe flag sampling | Choose only if system design includes explicit metastability mitigation and simplified flag logic suffices |
Compared with SN74ACT3631-20PBC and SN74ACT3641-20PBC, the SN74ACT3651-20PBC uniquely integrates mailbox registers and hardened retransmit logic-making it the sole option among these three for applications requiring concurrent command/data channeling and deterministic waveform replay without CPU intervention.
Availability
SN74ACT3651-20PBC is available at Aetrix Electronics and suitable for DSP acceleration, FPGA bridging, industrial PLC communication, and digital signal acquisition systems requiring stable component supply and long-term obsolescence management.
Supply support for SN74ACT3651-20PBC 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 SN74ACT3651-20PBC belongs to TI's ACT-family clocked FIFO product line, engineered specifically for deterministic, low-latency data buffering in mixed-clock-domain systems such as telecommunications infrastructure, test equipment, and real-time control.
FAQ
What is the maximum supported clock frequency for SN74ACT3651-20PBC?
The SN74ACT3651-20PBC supports clock frequencies up to 67 MHz on both CLKA and CLKB inputs. This rating is specified under standard commercial conditions (0°C to +70°C) and assumes proper setup/hold timing compliance for control signals like CSA, CSB, ENA, ENB, W/RA, and W/RB. The 67 MHz limit reflects worst-case propagation delay through internal logic and memory array, validated in TI's production characterization.
How does the synchronous retransmit feature work in SN74ACT3651-20PBC?
The SN74ACT3651-20PBC enters synchronous retransmit mode when RTM is high and OR is high, capturing the current FIFO output register content as the first retransmit word. Subsequent reads cycle through data starting at that point. RFM enables re-initiation of the retransmit sequence from the marked location. This mechanism operates independently of normal FIFO pointer advancement, preserving original data integrity during repeated access.
Can SN74ACT3651-20PBC operate with completely asynchronous CLKA and CLKB clocks?
Yes, SN74ACT3651-20PBC is explicitly designed for asynchronous clock operation. Its IR and AF flags are two-stage synchronized to CLKA, while OR and AE are two-stage synchronized to CLKB. This architecture minimizes metastability risk when CLKA and CLKB run at different frequencies or phases-verified in TI's SCZA004 application report on metastability performance.
What are the programming options for the almost-empty (AE) and almost-full (AF) offset registers in SN74ACT3651-20PBC?
The SN74ACT3651-20PBC supports three AE/AF offset programming methods: (1) preset values of 8 or 64 loaded automatically during reset, (2) parallel load from port A (two consecutive writes to FIFO), or (3) serial load via FS0/SD and FS1/SEN (22-bit sequence). All methods allow offset values from 1 to 2044, enabling precise buffer-level thresholds tailored to system-level flow control requirements.
Is SN74ACT3651-20PBC pin-compatible with other devices in the same family?
Yes, SN74ACT3651-20PBC is pin-to-pin compatible with SN74ACT3631-20PBC and SN74ACT3641-20PBC in the 120-pin PCB package. This compatibility extends to power, ground, clock, data, and control pin assignments-allowing drop-in replacement where functional differences (e.g., mailbox presence or flag synchronization depth) are acceptable within the target application.
SN74ACT3651-20PBC Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- *
- Package/Case:
- -
- Packaging:
- Bulk
- Product Status:
- Active
- Programmable:
- Not Verified
- Memory Size:
- -
- Function:
- -
- Data Rate:
- -
- Access Time:
- -
- Voltage - Supply:
- -
- Current - Supply (Max):
- -
- Bus Directional:
- -
- Expansion Type:
- -
- Programmable Flags Support:
- -
- Retransmit Capability:
- -
- FWFT Support:
- -
- Operating Temperature:
- -
- Mounting Type:
- -
- Supplier Device Package:
- -
SN74ACT3651-20PBC FAQ
1.How can I place an order for SN74ACT3651-20PBC through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ACT3651-20PBC 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 SN74ACT3651-20PBC reliable?
The price and inventory of SN74ACT3651-20PBC are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ACT3651-20PBC is usually 5 days.
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SN74ACT3651-20PBC orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ACT3651-20PBC 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 SN74ACT3651-20PBC?
For technical support, including SN74ACT3651-20PBC datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ACT3651-20PBC requirements.
6.How does Aetrix verify that SN74ACT3651-20PBC is sourced from the original manufacturer or authorized distributors?
All SN74ACT3651-20PBC 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 SN74ACT3651-20PBC meets industry standards.
7.What is the process for return or replacement of SN74ACT3651-20PBC?
All SN74ACT3651-20PBC units undergo pre-shipment inspection (PSI). If there is an issue with SN74ACT3651-20PBC, 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 SN74ACT3651-20PBC part is unused and in its original packaging.
Return procedure for SN74ACT3651-20PBC:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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