Texas Instruments SN74ACT3631-20DCB

Overview

SN74ACT3631-20DCB 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 operates in industrial temperature range (0°C to 70°C) and implements two-stage synchronized flags (IR/AF on CLKA, OR/AE on CLKB) for metastability mitigation in high-speed inter-processor data buffering applications.

For engineers reviewing the SN74ACT3631-20DCB datasheet, SN74ACT3631-20DCB pinout, SN74ACT3631-20DCB application, or SN74ACT3631-20DCB equivalent, key selection considerations include programmable almost-full/almost-empty offset registers, mailbox register support for control-message handshaking, dual-port SRAM architecture, and compatibility with microprocessor bus timing via CSA/CSB, W/RA/W/RB, and ENA/ENB control logic.

Technical Context

The SN74ACT3631-20DCB employs a dual-clock synchronous FIFO architecture with independent CLKA and CLKB domains, enabling asynchronous data transfer between port A and port B. Its 512 × 36-bit SRAM core supports write/read operations gated by low-to-high clock transitions, with input-ready (IR) and output-ready (OR) flags synchronized to CLKA and CLKB respectively.

It integrates two 36-bit mailbox registers (mail1/mail2), each with dedicated flag outputs (MBF1/MBF2), and supports three flag-offset programming modes: preset (8 or 64), parallel load from port A, or serial load via FS0/SD and FS1/SEN. Retransmit mode is initiated by RTM and controlled via RFM, allowing repeat reads from a user-marked location without disrupting ongoing writes.

Key Specifications

Pinout & Package

SN74ACT3631-20DCB is packaged in a 120-pin Thin Quad Flat Package (TQFP, PCB variant), with 36-bit bidirectional data buses on both ports, dual clock inputs (CLKA/CLKB), and dedicated control signals for chip select, enable, write/read direction, mailbox selection, and flag management.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74ACT3641-20DCB and SN74ACT3651-20DCB, the SN74ACT3631-20DCB uniquely combines mailbox registers, retransmit capability, and CLKA-synchronized AF/IR - making it the sole option for systems requiring integrated command/data coexistence and coefficient replay without external logic.

Availability

SN74ACT3631-20DCB is available at Aetrix Electronics and suitable for telecom line card buffering, DSP-based FIR filter interfaces, industrial PLC communication gateways, and legacy bus protocol bridges requiring stable component supply and long-term obsolescence management.

Supply support for SN74ACT3631-20DCB 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 SN74ACT3631-20DCB belongs to TI's ACT-family advanced CMOS FIFO portfolio, designed specifically for high-speed, low-latency inter-processor and cross-domain data buffering in telecom, industrial automation, and digital signal processing systems.

FAQ

What is the maximum clock frequency supported by the SN74ACT3631-20DCB?

The SN74ACT3631-20DCB supports clock frequencies up to 67 MHz on both CLKA and CLKB inputs. This specification is guaranteed across the full 0°C to 70°C operating temperature range and under standard VCC = 5 V conditions. The 67 MHz limit ensures reliable setup/hold timing for all control and data signals, including CSA, CSB, W/RA, W/RB, ENA, and ENB.

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

The SN74ACT3631-20DCB enters retransmit mode when RTM is high and OR is high, then a rising edge on CLKB marks the current FIFO output register content as the first retransmit word. Subsequent retransmits are triggered by RFM = high on rising CLKB. This allows repeated reads from a fixed SRAM location without affecting the main read pointer or disrupting ongoing writes - critical for FIR coefficient replay or protocol retransmission.

What are the three methods to program the almost-empty and almost-full offset registers in the SN74ACT3631-20DCB?

The SN74ACT3631-20DCB supports three offset programming methods selected at reset: (1) preset values (8 or 64) loaded automatically via FS1/FS0 states; (2) parallel load from port A, where the first two writes load Y then X registers using A8–A0; (3) serial load via FS0/SD, requiring 18 clocked bits (Y MSB first, X LSB last) with FS1/SEN acting as serial enable. All methods support offset values from 1 to 508.

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

Yes, the SN74ACT3631-20DCB is pin-to-pin compatible with SN74ACT3641-20DCB and SN74ACT3651-20DCB in the same 120-pin TQFP (PCB) package. However, functional differences exist: SN74ACT3641 omits mailbox registers and retransmit logic, while SN74ACT3651 relocates AF/IR synchronization to CLKB - requiring careful validation before substitution.

What is the role of the mailbox registers in the SN74ACT3631-20DCB?

The SN74ACT3631-20DCB includes two 36-bit mailbox registers: mail1 (written via port A, read via port B) and mail2 (written via port B, read via port A). MBA and MBB select mailbox access instead of FIFO, while MBF1 and MBF2 flags indicate new data availability. This enables concurrent control-message exchange (e.g., commands, status, ACKs) alongside bulk data transfer without consuming FIFO depth.