Texas Instruments SN74ACT3631-30PQ

Overview

SN74ACT3631-30PQ from Texas Instruments is a 512 × 36-bit clocked FIFO memory IC with dual asynchronous ports, supporting up to 67 MHz clock frequency, 11 ns read access time, and synchronous retransmit capability. It implements mailbox registers (Mail1/Mail2), programmable almost-full/almost-empty flags, and microprocessor-compatible control logic for buffered data transfer between independent clock domains.

For engineers reviewing the SN74ACT3631-30PQ datasheet, SN74ACT3631-30PQ pinout, SN74ACT3631-30PQ application, or SN74ACT3631-30PQ equivalent, key selection considerations include its 132-pin PQ package, CLKA/CLKB domain isolation, two-stage synchronized flag timing, 36-bit bidirectional port width, and support for serial/parallel flag offset programming - all critical for deterministic inter-processor communication and DSP interface design.

Technical Context

The SN74ACT3631-30PQ employs a dual-clock architecture with independent CLKA and CLKB inputs, enabling fully asynchronous operation between Port A and Port B. Its 512 × 36 SRAM core supports write/read operations gated on low-to-high transitions of respective clocks, with input-ready (IR) and output-ready (OR) flags synchronized to CLKA and CLKB via two-stage flip-flop chains to suppress metastability.

Flag offset registers (X for AE, Y for AF) are programmable via three methods: preset values (8 or 64), parallel load from Port A (A8–A0), or serial load through FS0/SD under FS1/SEN control. Retransmit mode uses shadow read pointer logic triggered by RTM/RFM signals, allowing repeat reads from a user-marked location without disrupting ongoing writes.

Key Specifications

Pinout & Package

SN74ACT3631-30PQ is housed in a 132-pin Plastic Quad Flat (PQ) package with 0.65 mm lead pitch, compliant with JEDEC MO-137. The package includes dedicated VCC/GND pairs per quadrant for noise suppression and thermal management in high-frequency FIFO operation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74ACT3641-30PQ and SN74ACT3651-30PQ, the SN74ACT3631-30PQ uniquely integrates both mailbox registers and synchronous retransmit - making it the only option among the three for applications demanding simultaneous command channeling and repeatable data playback without external logic.

Availability

SN74ACT3631-30PQ is available at Aetrix Electronics and suitable for DSP coefficient buffering, inter-processor communication, telecom data framing, industrial protocol gateway, and real-time audio processing requiring stable component supply across extended production lifecycles.

Supply support for SN74ACT3631-30PQ 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 timing and interface ICs.

The SN74ACT3631-30PQ 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 industrial control systems.

FAQ

What is the maximum supported clock frequency for SN74ACT3631-30PQ?

The SN74ACT3631-30PQ 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 67 MHz is not characterized and may result in timing violations or metastability in flag outputs.

How does the synchronous retransmit feature work in SN74ACT3631-30PQ?

The SN74ACT3631-30PQ implements synchronous retransmit using a shadow read pointer that locks the starting address when RTM is asserted high and OR is high. Subsequent reads triggered by RFM=high reload that address into the output register. This enables repeat playback of FIR coefficients or protocol headers without CPU involvement or external memory, preserving deterministic timing at up to 67 MHz.

Can SN74ACT3631-30PQ operate with CLKA and CLKB running at different frequencies?

Yes, SN74ACT3631-30PQ is explicitly designed for asynchronous operation: CLKA and CLKB may run at different frequencies, phases, or duty cycles. Its IR/AF flags are synchronized to CLKA, and OR/AE to CLKB, using two-stage flip-flop chains to ensure reliable flag assertion despite clock domain crossings - a core requirement validated in TI's SCZA004 metastability report.

What are the programming options for the almost-empty and almost-full flag offsets in SN74ACT3631-30PQ?

SN74ACT3631-30PQ supports three offset programming methods selected at reset via FS1/FS0: (1) preset values (8 or 64), (2) parallel load from Port A using A8–A0, or (3) serial load via FS0/SD under FS1/SEN control. All methods program independent X (AE) and Y (AF) registers with values from 1 to 508, enabling precise buffer watermark tuning for variable-latency systems.

Is SN74ACT3631-30PQ pin-compatible with other devices in the same family?

Yes, SN74ACT3631-30PQ is pin-to-pin compatible with SN74ACT3641-30PQ and SN74ACT3651-30PQ in the 132-pin PQ package. This allows direct substitution in existing PCB layouts when upgrading to or downgrading from mailbox and retransmit features - though firmware must be updated to leverage or disable those functions accordingly.