Texas Instruments SN74ACT3641-15PQ

Overview

SN74ACT3641-15PQ from Texas Instruments is a 1024 × 36 clocked FIFO memory IC with dual asynchronous ports, supporting up to 67 MHz clock frequency, 11 ns access time, and synchronous retransmit capability. It buffers high-speed data between microprocessor buses or DSP interfaces in telecom backplanes and real-time signal processing systems.

For engineers reviewing the SN74ACT3641-15PQ datasheet, SN74ACT3641-15PQ pinout, SN74ACT3641-15PQ application, or SN74ACT3641-15PQ equivalent, key selection criteria include dual-port flag synchronization (IR/AF on CLKA, OR/AE on CLKB), programmable almost-full/empty offsets, mailbox register support for control-message passing, and PQ-package compatibility with legacy 132-pin PCB layouts.

Technical Context

The SN74ACT3641-15PQ implements a dual-clock, synchronous FIFO architecture with independent CLKA and CLKB domains, enabling robust inter-clock-domain bridging. Its two-stage synchronized flags (IR/AF on CLKA; OR/AE on CLKB) mitigate metastability during asynchronous operation, while the shadow read pointer enables deterministic retransmit loops without halting writes.

It integrates two 36-bit mailbox registers (Mail1/Mail2) with dedicated MBA/MBB controls and flag outputs (MBF1/MBF2), allowing sideband command exchange alongside main data flow. Flag offset programming supports three modes-preset (8 or 64), parallel load via Port A, or serial load via FS0/SD-each validated for deterministic initialization timing.

Key Specifications

Pinout & Package

SN74ACT3641-15PQ uses a 132-pin Plastic Quad Flat (PQ) package with 0.65 mm pitch, compliant with Yamaichi socket IC51-1324-828. Pin numbering follows standard PQ top-view layout with corner pin 1 marked.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74ACT3631-15PQ and SN74ACT3651-15PQ, the SN74ACT3641-15PQ delivers optimal balance of depth, speed, and pin compatibility for mid-range real-time streaming-offering 2× the buffer of the 3631 without the die-area and power penalty of the 3651.

Availability

SN74ACT3641-15PQ is available at Aetrix Electronics and suitable for telecom infrastructure, DSP subsystems, industrial PLCs, and automated test equipment requiring stable component supply and long-term obsolescence management.

Supply support for SN74ACT3641-15PQ 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 SN74ACT3641-15PQ belongs to TI's ACT-family clocked FIFO product line, designed specifically for deterministic, low-latency data bridging between asynchronous high-speed digital subsystems in communications and industrial control.

FAQ

What is the maximum clock frequency supported by the SN74ACT3641-15PQ?

The SN74ACT3641-15PQ 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 read/write throughput. Exceeding 67 MHz may result in timing violations, particularly for setup/hold margins on flag outputs and mailbox register accesses. The SN74ACT3641-15PQ achieves this performance using low-power 0.8-µm Advanced CMOS technology.

How does the SN74ACT3641-15PQ handle metastability between asynchronous clocks CLKA and CLKB?

The SN74ACT3641-15PQ mitigates metastability through two-stage synchronization of all cross-domain signals: IR and AF flags are synchronized to CLKA, while OR and AE flags are synchronized to CLKB. This dual-flip-flop staging reduces the probability of metastable output states to less than 1 failure in 10⁹ clock cycles under worst-case skew conditions. The SN74ACT3641-15PQ datasheet confirms this architecture eliminates need for external synchronizers in typical inter-clock-domain applications.

Can the SN74ACT3641-15PQ be used for retransmit operations without halting writes?

Yes - the SN74ACT3641-15PQ supports concurrent retransmit and write operations. When RTM is asserted and OR is high, the device activates a shadow read pointer while continuing to accept new writes via CLKA. The AF flag remains valid relative to the shadow pointer, and IR reflects actual write-pointer position. This allows continuous data ingestion during repeated playback of stored segments, a core capability confirmed in the functional description and retransmit timing diagrams of the SN74ACT3641-15PQ datasheet.

What are the three methods to program the almost-empty (X) and almost-full (Y) offset registers in the SN74ACT3641-15PQ?

The SN74ACT3641-15PQ supports three mutually exclusive offset programming modes selected by FS0/FS1 during RST assertion: (1) Preset values (X=Y=8 or X=Y=64), (2) Parallel load from Port A (two consecutive writes to load Y then X), and (3) Serial load via FS0/SD with 20-bit sequence (MSB of Y first, LSB of X last). All methods are fully documented in the SN74ACT3641-15PQ datasheet Section "Almost-Empty Flag and Almost-Full Flag Offset Programming" and verified in application reports SCAA007 and SCZA004.

Is the SN74ACT3641-15PQ pin-compatible with other devices in the same family?

Yes - the SN74ACT3641-15PQ is explicitly stated as pin-to-pin compatible with SN74ACT3631-15PQ (512×36) and SN74ACT3651-15PQ (2048×36) in the official datasheet. This compatibility extends to all 132 pins, including power, ground, control, data, and flag signals, enabling direct substitution on existing PQ-package PCBs without layout changes. The SN74ACT3641-15PQ maintains identical timing parameters and electrical characteristics across the family.