Texas Instruments SN74ACT7805-20DLR

Overview

SN74ACT7805-20DLR 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 50 MHz (–20 speed grade), delivers 12 ns access time with 50-pF load, and features synchronized input-ready (IR) and output-ready (OR) flags. It is used in high-speed digital interface bridging, such as between DSPs and peripherals.

For engineers reviewing the SN74ACT7805-20DLR datasheet, SN74ACT7805-20DLR pinout, SN74ACT7805-20DLR application, or SN74ACT7805-20DLR equivalent, key selection criteria include its 50-MHz maximum clock frequency, programmable almost-full/almost-empty flag offsets, bidirectional configuration capability without external logic, and compatibility with SN74ACT7803/SN74ACT7813 for footprint reuse.

Technical Context

The SN74ACT7805-20DLR implements a synchronous dual-clock FIFO architecture with independent write and read pointer control, status flag synchronization to respective clocks (IR to WRTCLK, OR to RDCLK), and reset-initiated initialization of all flags. Its internal 256 × 18-bit RAM uses low-power advanced CMOS technology with distributed VCC/GND pins and TI's patented Output Edge Control (OEC™) to suppress simultaneous switching noise.

It supports programmable AF/AE flag offsets (X/Y) via D0–D6 during reset, defaulting to X = Y = 32. The FIFO requires four rising edges on both WRTCLK and RDCLK under RESET low to fully clear synchronizing registers, ensuring deterministic flag states (IR/OF/HF low, AF/AE high) after power-up.

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, compliant with JEDEC MS-012AC.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74ACT7803-20DLR and SN74ACT7813-20DLR, the SN74ACT7805-20DLR uniquely balances programmable flow control (via PEN/D0–D6) with minimal feature overhead-making it optimal for cost-sensitive, high-volume designs requiring tunable buffer thresholds without serial interface complexity.

Availability

SN74ACT7805-20DLR is available at Aetrix Electronics and suitable for telecom infrastructure, industrial automation, test equipment, and embedded DSP interface applications requiring stable component supply and long-term obsolescence management.

Supply support for SN74ACT7805-20DLR 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 industrial and communications ICs.

The SN74ACT7805-20DLR belongs to TI's Widebus™ family of high-speed logic FIFOs, engineered specifically for robust clock-domain crossing in mission-critical digital systems where deterministic latency and noise immunity are essential.

FAQ

What is the maximum clock frequency supported by the SN74ACT7805-20DLR?

The SN74ACT7805-20DLR supports a maximum clock frequency of 50 MHz for both read and write operations, as specified in its –20 speed grade. This rating applies under recommended operating conditions (VCC = 4.5 V to 5.5 V, TA = 0°C to 70°C) with CL = 50 pF. At this rate, the device sustains full 18-bit data throughput without violating setup/hold or propagation delay limits defined in the timing table.

How does the SN74ACT7805-20DLR handle reset initialization?

The SN74ACT7805-20DLR requires an asynchronous reset sequence: RESET must be held low while at least four rising edges occur on both WRTCLK and RDCLK. This clears internal synchronizers and initializes IR, OR, and HF flags low and AF/AE high. The FIFO must be reset upon power-up to ensure deterministic flag states and prevent undefined behavior during first access.

Can the SN74ACT7805-20DLR be used for bidirectional data buffering?

Yes, the SN74ACT7805-20DLR supports bidirectional buffering when two units are configured per Figure 8 in the datasheet. One device handles A→B direction (D inputs tied to A-side, Q outputs to B-side), the other handles B→A (D inputs from B-side, Q outputs to A-side), sharing common clocks and enables-no additional logic required.

What is the function of the PEN pin on the SN74ACT7805-20DLR?

The PEN (Program Enable) pin on the SN74ACT7805-20DLR allows programming of the almost-full/almost-empty flag offsets (X and Y) during reset. When PEN is low and WRTCLK rises, the binary value on D0–D6 is latched as the X offset; a second WRTCLK rise with PEN low sets Y. If PEN remains high, default values X = Y = 32 are used.

Does the SN74ACT7805-20DLR support width expansion beyond 18 bits?

Yes, the SN74ACT7805-20DLR supports word-width expansion: two devices can be cascaded to form a 256 × 36-bit FIFO (Figure 9). This is achieved by connecting shared WRTCLK/RDCLK, enabling coordinated write/read enables, and paralleling D/Q buses while managing OE/IR/OR signals per unit to maintain independent status reporting.