Texas Instruments SN74ACT7801-18FNR

Overview

SN74ACT7801-18FNR from Texas Instruments is a 1024 × 18-bit asynchronous FIFO memory IC with independent read/write clocks, 15 ns access time (50-pF load), programmable almost-full/almost-empty flag, and 3-state outputs. It serves as a data rate-matching buffer in high-speed digital systems such as bus bridges and communication controllers.

For engineers reviewing the SN74ACT7801-18FNR datasheet, SN74ACT7801-18FNR pinout, SN74ACT7801-18FNR application, or SN74ACT7801-18FNR equivalent, key selection criteria include its dual-clock synchronization capability, 18-bit parallel I/O width, 68-pin PLCC package, fast 35 MHz max clock frequency, and support for cascading in word depth or width.

Technical Context

The SN74ACT7801-18FNR implements a fully asynchronous FIFO architecture with separate write-clock (WRTCLK) and read-clock (RDCLK) domains, enabling independent data ingestion and egress at up to 35 MHz. Its internal 1024-word × 18-bit RAM array uses synchronous pointer control logic to manage read/write addresses without external arbitration.

Status flags-including input-ready (IR), output-ready (OR), half-full (HF), and programmable almost-full/almost-empty (AF/AE)-are driven synchronously with their respective clocks. The AF/AE offset value (X = 0–511) is user-definable via D0–D8 during reset, or defaults to X = 256.

Key Specifications

Pinout & Package

SN74ACT7801-18FNR is housed in a 68-pin Plastic Leaded Chip Carrier (PLCC-FN) package with J-leads, measuring 24.33 mm × 24.33 mm × 4.29 mm (max height). Pin 1 is located at the corner adjacent to the index notch.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74ACT7804-18FNR and IDT7203L15J, the SN74ACT7801-18FNR delivers the highest clock rate and most flexible flag programming in a single 68-pin PLCC package, making it optimal for high-throughput, 5-V-only legacy upgrades where minimal footprint and maximum timing margin are essential.

Availability

SN74ACT7801-18FNR is available at Aetrix Electronics and suitable for industrial control systems, legacy equipment retrofits, and high-speed bus bridge designs requiring stable component supply across extended production lifecycles.

Supply support for SN74ACT7801-18FNR 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 90 years of innovation in high-reliability components.

The SN74ACT7801-18FNR belongs to TI's Widebus™ family of high-speed interface ICs, designed specifically for robust data buffering in industrial, telecom, and computing infrastructure where clock domain isolation and deterministic latency are critical.

FAQ

What is the maximum operating clock frequency supported by the SN74ACT7801-18FNR?

The SN74ACT7801-18FNR supports a maximum clock frequency of 35 MHz for both read and write operations, as specified in the recommended operating conditions table. This rating assumes CL = 50 pF and VCC = 4.5 V to 5.5 V. At 25 MHz, supply current is 230 mA; above that, ICC increases linearly per TI's formula: ICC = 230 mA + (6 mA × [f − 25 MHz]). The SN74ACT7801-18FNR achieves this performance while maintaining 15 ns access time and full flag functionality.

How is the almost-full/almost-empty flag programmed on the SN74ACT7801-18FNR?

The almost-full/almost-empty (AF/AE) flag on the SN74ACT7801-18FNR is programmed during reset using the define almost-full (DAF) input. To set a custom offset X, assert DAF low, then pulse RESET low while DAF remains low-the binary value on D0–D8 is latched as X. If DAF is held high during RESET, the default X = 256 is used. The AF/AE flag then goes high when FIFO occupancy ≤ (X + 1) or ≥ (1025 − X) words. This behavior is fully implemented in the SN74ACT7801-18FNR's internal status logic.

Can the SN74ACT7801-18FNR be cascaded to increase memory depth or width?

Yes, the SN74ACT7801-18FNR supports both word-depth and word-width expansion without external logic. For depth expansion (e.g., 2048 × 18), connect WRTCLK, RDCLK, and all enables in parallel across devices; OR and IR flags chain to adjust timing (OR asserts after N × 3 RDCLK cycles). For width expansion (e.g., 1024 × 36), tie corresponding clocks/enables and split D/Q buses across devices. All control and flag signals remain functional in cascaded configurations of the SN74ACT7801-18FNR.

What are the power supply requirements for reliable operation of the SN74ACT7801-18FNR?

The SN74ACT7801-18FNR requires a single 4.5 V to 5.5 V supply (VCC) with multiple distributed VCC and GND pins to suppress noise. Absolute maximum VCC is 7 V, but operation outside 4.5–5.5 V voids specifications. Total supply current ranges from 20 mA (standby) to 230 mA + (6 mA × [f − 25 MHz]) at full clock rate. Decoupling capacitors (0.1 µF ceramic near each VCC pin) are mandatory to maintain signal integrity and prevent metastability in the SN74ACT7801-18FNR's dual-clock architecture.

Is the SN74ACT7801-18FNR pin-compatible with other members of the 'ACT7801 family?

Yes, the SN74ACT7801-18FNR shares identical pinout and functionality with other speed grades in the 'ACT7801 family packaged in 68-pin PLCC (FN), including SN74ACT7801-15FNR and SN74ACT7801-20FNR. Differences are limited to AC timing parameters: access time (15/18/20 ns) and max clock frequency (40/35/28.5 MHz). All share the same DC characteristics, flag behavior, reset sequence, and expansion capabilities-making the SN74ACT7801-18FNR a direct drop-in option where 35 MHz operation and 18 ns timing are required.