Texas Instruments SN74ACT7805-40DL

Overview

SN74ACT7805-40DL from Texas Instruments is a 256 × 18-bit clocked FIFO memory IC designed for asynchronous data buffering between independent clock domains. It supports free-running, asynchronous or coincident read/write clocks up to 25 MHz, delivers 20 ns access time (CL = 50 pF), features synchronized input-ready (IR) and output-ready (OR) flags, and operates across 0°C to 70°C for industrial data-path synchronization.

For engineers reviewing the SN74ACT7805-40DL datasheet, SN74ACT7805-40DL pinout, SN74ACT7805-40DL application, or SN74ACT7805-40DL equivalent, key selection criteria include its 25-MHz maximum clock frequency, programmable almost-full/almost-empty flag offsets, bidirectional configuration capability without external logic, and DL-package pin compatibility with SN74ACT7803/SN74ACT7813.

Technical Context

The SN74ACT7805-40DL implements a synchronous dual-clock FIFO architecture with independent write and read pointer control, status-flag logic synchronized to respective clocks (IR to WRTCLK, OR to RDCLK), and reset-initiated initialization of all flags. Its 256-word × 18-bit RAM core uses low-power advanced CMOS technology with patented output edge control (OEC™) to suppress simultaneous switching noise.

It supports programmable AF/AE flag thresholds via D0–D6 and PEN during reset, enables width expansion to 36 bits using two devices, and allows bidirectional data flow by pairing two units - all without additional glue logic. The device requires four rising edges on both WRTCLK and RDCLK under RESET assertion to fully clear internal synchronizers.

Key Specifications

Pinout & Package

Packaged in a 56-pin Shrink Small-Outline (DL) package with 300-mil body width and 25-mil center-to-center lead pitch, optimized for high-density PCB layouts while maintaining compatibility with industry-standard SOIC footprints.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74ACT7803-40DL and SN74ACT7813-40DL, the SN74ACT7805-40DL uniquely combines programmable AF/AE thresholds, IR/OR synchronization, and HF flag in one pin-compatible DL package - enabling tighter buffer management and reduced software overhead in real-time embedded systems.

Availability

SN74ACT7805-40DL is available at Aetrix Electronics and suitable for high-speed data acquisition, industrial PLC communication bridges, video frame buffering, and test equipment pattern generation requiring stable component supply and long-term obsolescence planning.

Supply support for SN74ACT7805-40DL 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 industrial, automotive, and communications markets.

The SN74ACT7805-40DL belongs to TI's Widebus™ family of high-speed interface logic, engineered specifically for robust asynchronous data buffering in mixed-clock-domain systems with stringent timing and noise immunity requirements.

FAQ

What is the maximum clock frequency supported by the SN74ACT7805-40DL?

The SN74ACT7805-40DL supports a maximum clock frequency of 25 MHz for both read and write operations under recommended operating conditions (VCC = 4.5 V to 5.5 V, TA = 0°C to 70°C). This rating is confirmed in the timing requirements table of the SCAS201B datasheet, where the 'ACT7805-40 variant specifies 25 MHz as the upper limit for reliable operation with 12 ns minimum pulse width.

How does the SN74ACT7805-40DL handle reset initialization?

The SN74ACT7805-40DL requires an asynchronous reset sequence: RESET must be held low while at least four rising edges occur on both WRTCLK and RDCLK. This clears the synchronizing registers and initializes IR, OR, and HF flags low and AF/AE high. The FIFO must be reset upon power-up to guarantee deterministic flag states and memory readiness, as stated in the functional description section of the datasheet.

Can the SN74ACT7805-40DL be used for bidirectional data flow?

Yes, the SN74ACT7805-40DL supports bidirectional data flow when two devices are configured per Figure 8 in the SCAS201B datasheet. Each unit handles one direction (A→B and B→A), sharing common clock and control signals. No additional logic is needed - the architecture inherently supports this mode through dedicated enable and flag routing, making it ideal for full-duplex communication bridges.

What is the purpose of the PEN pin on the SN74ACT7805-40DL?

The PEN (Program Enable) pin on the SN74ACT7805-40DL controls programming of the almost-full/almost-empty (AF/AE) flag offsets. After reset and before the first write, asserting PEN low during a WRTCLK rising edge latches D0–D6 as the almost-empty offset (X); a second low PEN pulse sets the almost-full offset (Y). PEN must remain high to retain default X=Y=32, as detailed in the Terminal Functions and Application Information sections.

Does the SN74ACT7805-40DL support width expansion beyond 18 bits?

Yes, the SN74ACT7805-40DL supports width expansion to 36 bits using two devices, as shown in Figure 9 of the SCAS201B datasheet. The units are connected in parallel with shared clocks and enables, while Q outputs are concatenated. This preserves all timing specifications and flag behaviors without requiring external logic, enabling scalable buffer design for wider data buses.