Texas Instruments SN74ACT7811-18FN

Overview

SN74ACT7811-18FN 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 68-pin PLCC (FN) package. It enables high-speed data buffering between mismatched bus domains in telecom line cards and industrial controller backplanes.

For engineers reviewing the SN74ACT7811-18FN datasheet, SN74ACT7811-18FN pinout, SN74ACT7811-18FN application, or SN74ACT7811-18FN equivalent, key selection criteria include independent RDCLK/WRTCLK synchronization, 40 MHz max clock frequency, 18-bit parallel I/O, AF/AE flag programmability, and cascading capability for depth/width expansion.

Technical Context

The SN74ACT7811-18FN implements dual-clock FIFO architecture with separate write-pointer and read-pointer logic synchronized to WRTCLK and RDCLK respectively. Its status flags-IR, OR, HF, AF/AE, and DAF-are driven synchronously to their respective clocks, enabling deterministic timing in interrupt-driven systems.

It supports bit-parallel 18-bit data transfer with noninverting outputs, high-output drive (–8 mA / +16 mA), and operates across 4.5 V–5.5 V supply. The device uses TTL-compatible input thresholds (VIH = 2 V, VIL = 0.8 V) and features cascading control via IR/OR handshake signals for multi-device depth expansion.

Key Specifications

Pinout & Package

SN74ACT7811-18FN is housed in a 68-pin plastic J-leaded chip carrier (PLCC, FN package), measuring 24.2 mm × 24.2 mm with 1.27-mm lead pitch. The package is surface-mountable, JEDEC MS-018 compliant, and features internal power/ground plane distribution optimized for low-noise FIFO operation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74ACT7881-18FN and SN74ACT7884-18FN, the SN74ACT7811-18FN uniquely balances programmable flow control, minimal pin count, and direct pin compatibility-making it optimal for cost-sensitive, single-FIFO designs needing adaptive buffer management.

Availability

SN74ACT7811-18FN is available at Aetrix Electronics and suitable for telecom infrastructure, industrial automation, medical imaging, and test equipment applications requiring stable component supply and long-term obsolescence planning.

Supply support for SN74ACT7811-18FN 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 over 50 years of innovation in high-reliability interface and memory products.

The SN74ACT7811-18FN belongs to TI's Widebus™ family of high-speed FIFOs designed specifically for asynchronous data rate bridging in communications, industrial, and instrumentation systems.

FAQ

What is the maximum clock frequency supported by the SN74ACT7811-18FN?

The SN74ACT7811-18FN supports a maximum clock frequency of 35 MHz for both read and write operations, as specified for the -18 speed grade. This corresponds to a 28.5 ns minimum clock period and enables reliable operation in high-throughput data pipelines such as telecom framer interfaces and real-time signal acquisition systems. The SN74ACT7811-18FN achieves this performance while maintaining 15 ns access time at 50-pF load.

How is the almost-full/almost-empty (AF/AE) flag programmed on the SN74ACT7811-18FN?

The AF/AE flag on the SN74ACT7811-18FN is programmed during reset using the DAF input and D0–D8 data lines. To define a custom offset X, assert DAF low, then apply the 9-bit binary value to D0–D8 and pulse RESET low-to-high. If DAF remains high during RESET, the default X = 256 is used. This programming occurs once per power-on or hard reset and determines the fill-level thresholds for AF/AE assertion. The SN74ACT7811-18FN does not support runtime reprogramming.

Can the SN74ACT7811-18FN be cascaded for increased memory depth or width?

Yes, the SN74ACT7811-18FN supports both word-width and word-depth expansion. For depth expansion (e.g., 2048×18), connect IR and OR flags between devices to form a daisy-chained handshake chain; timing scales linearly with N devices (N×3 RDCLK cycles for first read). For width expansion (e.g., 1024×36), tie corresponding clocks/enables and route D18–D35/Q18–Q35 to a second SN74ACT7811-18FN. All expansion modes retain identical timing constraints and require no external glue logic.

What are the voltage and current specifications for the SN74ACT7811-18FN I/O pins?

The SN74ACT7811-18FN operates from a 4.5 V to 5.5 V supply and features TTL-compatible input thresholds (VIH = 2.0 V min, VIL = 0.8 V max). Output drive is –8 mA (high) and +16 mA (low) into 50-Ω loads, supporting direct connection to 5-V buses without level shifters. Input leakage is ±5 µA, and output off-state leakage is ±5 µA. These specs ensure robust noise immunity and compatibility with legacy 5-V logic families in industrial and telecom systems.

Is the SN74ACT7811-18FN pin-compatible with other members of the SN74ACT78xx family?

Yes, the SN74ACT7811-18FN is pin-to-pin compatible with SN74ACT7881, SN74ACT7882, and SN74ACT7884 in the same FN (68-pin PLCC) package. This allows drop-in replacement for functional evaluation or design reuse, though feature sets differ: SN74ACT7881 lacks DAF-programmable AF/AE, while SN74ACT7884 adds multi-FIFO sync registers. Pin compatibility extends to power, ground, clock, enable, data, and flag terminals-no PCB redesign is needed when substituting within this family.