Texas Instruments SN74ACT7811-25PN

Overview

SN74ACT7811-25PN from Texas Instruments is a 1024 × 18-bit clocked first-in, first-out (FIFO) memory IC with independent asynchronous read/write clocks, 15 ns access time at 50-pF load, programmable almost-full/almost-empty flag, and 80-pin LQFP (PN) package. It enables high-speed data buffering between mismatched clock domains in digital communication interfaces.

For engineers reviewing the SN74ACT7811-25PN datasheet, SN74ACT7811-25PN pinout, SN74ACT7811-25PN application, or SN74ACT7811-25PN equivalent, key selection considerations include its 16.7 MHz maximum clock frequency, dual-clock synchronization capability, 18-bit parallel I/O, programmable status flags (AF/AE, HF, IR, OR), and compatibility with ACT logic family voltage levels.

Technical Context

The SN74ACT7811-25PN implements a synchronous FIFO architecture with separate write clock (WRTCLK) and read clock (RDCLK) domains, each driving independent pointer logic. Its internal 1024 × 18-bit RAM array supports concurrent write and read operations without bus contention.

Status flag generation is fully integrated: AF/AE boundary is programmable via DAF input and D0–D8 during reset, HF asserts at ≥513 words, and IR/OR are synchronized to WRTCLK and RDCLK respectively-ensuring deterministic timing for handshake protocols.

Key Specifications

Pinout & Package

SN74ACT7811-25PN uses an 80-pin thin quad flat package (LQFP, PN), measuring 12.2 mm × 12.2 mm × 1.4 mm, with 0.5-mm lead pitch and exposed thermal pad. Pin numbering follows JEDEC MS-026 standard.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74ACT7881-25PN and SN74ACT7882-25PN, the SN74ACT7811-25PN uniquely delivers programmable AF/AE functionality within a single 18-bit-wide device, enabling adaptive flow control without layout or firmware compromises required by fixed-threshold or half-width alternatives.

Availability

SN74ACT7811-25PN is available at Aetrix Electronics and suitable for telecom infrastructure, industrial automation, video processing, and legacy bus interface applications requiring stable component supply and long-term obsolescence management.

Supply support for SN74ACT7811-25PN 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 company founded in 1930, specializing in analog, embedded processing, and logic solutions with broad industrial and communications portfolio coverage.

The SN74ACT7811-25PN belongs to TI's Widebus™ family of high-speed interface ICs, designed specifically for clock-domain isolation, data rate matching, and deterministic buffering in real-time digital systems.

FAQ

What is the maximum clock frequency supported by the SN74ACT7811-25PN?

The SN74ACT7811-25PN supports a maximum clock frequency of 16.7 MHz for both WRTCLK and RDCLK inputs, as specified in the timing requirements table for the -25 speed grade. This rating assumes operation within recommended conditions (VCC = 4.5 V to 5.5 V, TA = 0°C to 70°C, CL = 50 pF). Exceeding this frequency may result in setup/hold violations or metastability in flag outputs.

How is the almost-full/almost-empty (AF/AE) flag programmed on the SN74ACT7811-25PN?

The AF/AE flag on the SN74ACT7811-25PN is programmed during reset using the DAF input and D0–D8 data lines. To set a custom offset X, drive DAF low, then apply the 9-bit value to D0–D8 before taking RESET high. To use the default X = 256, hold DAF high during reset. The SN74ACT7811-25PN implements this behavior per the SCAS151C datasheet revision February 1996.

Does the SN74ACT7811-25PN support cascading for increased memory depth or width?

Yes, the SN74ACT7811-25PN supports both word-width and word-depth expansion. For width expansion (e.g., 1024 × 36-bit), connect D18–D35 and Q18–Q35 to a second device while sharing clocks and enables. For depth expansion (e.g., 2048 × 18-bit), daisy-chain IR/OR flags and adjust timing per the (N × 2) and (N × 3) cycle rules documented for the SN74ACT7811-25PN.

What are the key timing parameters affecting read latency in the SN74ACT7811-25PN?

Read latency in the SN74ACT7811-25PN is governed by tpd(RDCLK↑ → Any Q) = 4 ns (min) to 25 ns (max), plus OE assertion timing (ten = 2–11 ns). The first word appears on Q0–Q17 after three RDCLK cycles post-initial write. All subsequent reads occur on each RDCLK rising edge when RDEN1, RDEN2, OE, and OR are high-making total latency dependent on flag synchronization and enable setup.

Is the SN74ACT7811-25PN pin-compatible with other members of the SN74ACT78xx family?

Yes, the SN74ACT7811-25PN is pin-to-pin compatible with SN74ACT7881, SN74ACT7882, and SN74ACT7884 in the same 80-pin PN package, as explicitly stated in the datasheet. This allows direct substitution in existing layouts when functional requirements align-though differences in memory width (18-bit vs. 9-bit) and AF/AE programmability must be verified for system compatibility.