Texas Instruments SN74ACT3631-30PCB

Overview

SN74ACT3631-30PCB 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 programmable almost-full/empty flags synchronized to independent CLKA and CLKB clocks. It enables high-throughput data buffering between microprocessor buses in telecom line cards and DSP interface systems.

For engineers reviewing the SN74ACT3631-30PCB datasheet, SN74ACT3631-30PCB pinout, SN74ACT3631-30PCB application, or SN74ACT3631-30PCB equivalent, key selection criteria include its 120-pin thin quad flat (PCB) package, synchronous retransmit capability, mailbox register support, and pin-to-pin compatibility with SN74ACT3641 and SN74ACT3651 for scalable FIFO designs.

Technical Context

The SN74ACT3631-30PCB implements a dual-clock FIFO architecture with independent CLKA and CLKB domains, each driving separate 36-bit bidirectional data ports (A0–A35 and B0–B35). Its 512 × 36 SRAM core supports concurrent read/write operations, two-stage flag synchronization, and retransmit logic controlled by RTM and RFM inputs.

Flag generation uses programmable offset registers (X for AE, Y for AF), loaded via parallel port-A writes, serial bitstream, or preset values (8 or 64). Mailbox registers (Mail1/Mail2) operate independently of FIFO storage and are flagged by MBF1/MBF2 outputs synchronized to respective port clocks.

Key Specifications

Pinout & Package

SN74ACT3631-30PCB 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 orientation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74ACT3641-30PCB, SN74ACT3631-30PCB adds mailbox registers and retransmit capability without increasing pin count or power; versus SN74ACT3651-30PCB, it trades extended temperature rating for lower cost in commercial applications.

Availability

SN74ACT3631-30PCB is available at Aetrix Electronics and suitable for telecom infrastructure, DSP interface design, and industrial motion control applications requiring stable component supply across long production lifecycles.

Supply support for SN74ACT3631-30PCB 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 experience in high-reliability timing and interface ICs.

The SN74ACT3631-30PCB belongs to TI's ACT-family clocked FIFO product line, designed specifically for deterministic, low-latency data buffering between asynchronous digital subsystems in communications and computing equipment.

FAQ

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

The SN74ACT3631-30PCB 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 defines the upper limit for reliable synchronous operation of port-A and port-B transfers. Exceeding this frequency may result in timing violations and metastability in flag outputs.

How does the retransmit function work in SN74ACT3631-30PCB?

The SN74ACT3631-30PCB implements synchronous retransmit using RTM and RFM control inputs. When RTM is high and OR is asserted, a rising edge on CLKB marks the current output register content as the first retransmit word. Subsequent retransmits are triggered by RFM-high edges on CLKB, reloading the shadow read pointer. This enables repeat playback without CPU overhead or memory copy operations.

Can SN74ACT3631-30PCB be used with only one clock domain?

Yes, SN74ACT3631-30PCB supports single-clock-domain operation: CLKA and CLKB may be tied together or driven by the same source. The device retains full functionality-including flag synchronization, mailbox access, and retransmit-even when clocks are coincident. However, two-stage flag sync remains active, adding minimal latency but ensuring robustness if clock skew arises later.

What package type does SN74ACT3631-30PCB use?

SN74ACT3631-30PCB uses a 120-pin thin quad flat package (TQFP) designated "PCB" by Texas Instruments, with 0.4 mm lead pitch and JEDEC-standard footprint. This package is distinct from the 132-pin PQ variant and is not interchangeable without PCB redesign due to differing pin count, spacing, and thermal pad configuration.

How are the almost-empty and almost-full flags programmed on SN74ACT3631-30PCB?

SN74ACT3631-30PCB supports three programming methods for AE (X) and AF (Y) offset registers: preset values (8 or 64) selected via FS0/FS1 at reset, parallel load from port-A data lines A8–A0, or serial bitstream via FS0/SD synchronized to CLKA. All methods allow offset values from 1 to 508, enabling precise buffer-level thresholds tailored to system-level flow control requirements.