Texas Instruments SN74ACT3631-20PCB

Overview

SN74ACT3631-20PCB from Texas Instruments is a 512 × 36-bit clocked FIFO memory IC with dual asynchronous ports, 67 MHz clock support, 11 ns read access time, and synchronous retransmit capability. It buffers data between port A and port B in high-speed digital systems requiring deterministic latency and mailbox-based inter-processor communication.

For engineers reviewing the SN74ACT3631-20PCB datasheet, SN74ACT3631-20PCB pinout, SN74ACT3631-20PCB application, or SN74ACT3631-20PCB equivalent, key selection criteria include programmable almost-full/empty flag offsets, two-stage synchronized status flags, dual 36-bit mailbox registers, and pin-to-pin compatibility with SN74ACT3641/SN74ACT3651 for scalable datapath expansion.

Technical Context

The SN74ACT3631-20PCB implements a dual-clock FIFO architecture with independent CLKA and CLKB domains, enabling fully asynchronous operation between port A and port B. Its 512 × 36 SRAM core supports synchronous read-retransmit via shadow read pointer and programmable flag offset registers (X for AE, Y for AF).

Flag synchronization uses two-stage flip-flop chains: IR and AF are synchronized to CLKA; OR and AE to CLKB. Mailbox registers (mail1/mail2) operate independently of FIFO storage, with MBA/MBB controls and MBF1/MBF2 status flags tied to port-specific clock edges.

Key Specifications

Pinout & Package

SN74ACT3631-20PCB is housed in a 120-pin Thin Quad Flat Package (TQFP), designated PCB in TI documentation. Pin numbering follows standard top-view layout with VCC/GND distributed across multiple pins for noise reduction and thermal management.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar clocked FIFO memory applications.

Compared with SN74ACT3641-20PCB, SN74ACT3631-20PCB adds mailbox registers and retransmit capability at identical speed and depth; versus SN74ACT3651-20PCB, it offers lower default AF threshold and identical functionality otherwise-making it optimal for tighter flow control tuning.

Availability

SN74ACT3631-20PCB is available at Aetrix Electronics and suitable for telecom infrastructure, DSP co-processing, industrial PLC backplanes, and video frame synchronization requiring stable component supply and long-term obsolescence management.

Supply support for SN74ACT3631-20PCB 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 broad industrial and automotive qualification coverage.

The SN74ACT3631-20PCB belongs to TI's advanced clocked FIFO family designed for high-reliability, multi-clock-domain data buffering in communications, computing, and real-time control systems.

FAQ

What is the maximum supported clock frequency for SN74ACT3631-20PCB?

The SN74ACT3631-20PCB supports clock frequencies up to 67 MHz on both CLKA and CLKB inputs. This specification is guaranteed across the commercial temperature range (0°C to 70°C) and enables use in high-speed digital interfaces such as DSP links and telecom framer buffers. The 11 ns read access time aligns with this clock rate to ensure timing closure in synchronous designs using SN74ACT3631-20PCB.

How does the synchronous retransmit feature work in SN74ACT3631-20PCB?

The synchronous retransmit feature in SN74ACT3631-20PCB allows repeated reading of FIFO data starting from a user-selected location. It is activated by asserting RTM high while OR is high, then using RFM to reset the read pointer. This enables looped delivery of coefficient sets or test patterns without CPU overhead. Retransmit mode maintains independent shadow and current read pointers, ensuring SN74ACT3631-20PCB retains full write capability even during repeated reads.

Can SN74ACT3631-20PCB operate with completely asynchronous CLKA and CLKB clocks?

Yes, SN74ACT3631-20PCB is explicitly designed for asynchronous CLKA and CLKB operation. Its IR and AF flags are two-stage synchronized to CLKA, while OR and AE are synchronized to CLKB-minimizing metastability risk during clock domain crossings. The functional block diagram and terminal descriptions confirm independent clock domains, making SN74ACT3631-20PCB suitable for bridging processors or peripherals with unrelated clock sources.

What are the programming methods for the almost-empty and almost-full flag offsets in SN74ACT3631-20PCB?

SN74ACT3631-20PCB supports three flag offset programming methods: (1) automatic load of preset values (8 or 64) selected by FS1/FS0 at reset; (2) parallel load from port A data lines A8–A0; or (3) serial load via FS0/SD bitstream synchronized to CLKA. All methods program X (AE offset) and Y (AF offset) registers with values from 1 to 508. The method is selected during RST assertion, and SN74ACT3631-20PCB behavior is fully defined per Table 1 in the datasheet.

Is SN74ACT3631-20PCB pin-compatible with other devices in the same family?

Yes, SN74ACT3631-20PCB is pin-to-pin compatible with SN74ACT3641-20PCB and SN74ACT3651-20PCB in the same 120-pin PCB package. This allows direct substitution in existing PCB layouts for functional upgrades (e.g., adding mailbox or retransmit capability) or parameter tuning (e.g., default AF offset). The pinout diagram and terminal function table confirm identical signal mapping across all three variants of SN74ACT3631-20PCB.