Texas Instruments SN74ACT7808-20FN

Overview

SN74ACT7808-20FN from Texas Instruments is a 2048 × 9-bit strobed FIFO memory IC designed for high-speed data buffering between asynchronous clock domains. It delivers 15 ns access time, 50 MHz maximum data rate, and supports programmable almost-full/almost-empty flags. It is used in digital communications interfaces requiring depth/width expansion and real-time data flow control.

For engineers reviewing the SN74ACT7808-20FN datasheet, SN74ACT7808-20FN pinout, SN74ACT7808-20FN application, or SN74ACT7808-20FN equivalent, key selection criteria include its 44-pin LCC package, 2048-word depth, 9-bit parallel I/O, asynchronous load/unload clocks, and programmable status flag offsets - all critical for buffer synchronization in legacy industrial and telecom systems.

Technical Context

The SN74ACT7808-20FN implements a dual-clock, bit-parallel FIFO architecture with independent write (LDCK) and read (UNCK) pointers managed by internal stack logic. It uses low-power advanced CMOS technology and includes dedicated reset, output-enable, and cascade-enable circuitry to support depth and width expansion without external glue logic.

Status monitoring is handled via four dedicated flags: FULL (active-low), EMPTY (active-low), HF (half-full, active-high at ≥1024 words), and AF/AE (programmable offset flag). The AF/AE flag supports configurable thresholds (X/Y) up to 1023 words, set via D0–D8 and DP9 during reset-initiated programming cycles with PEN control.

Key Specifications

Pinout & Package

SN74ACT7808-20FN is housed in a 44-pin plastic leaded chip carrier (PLCC, FN package), surface-mountable with J-lead geometry and 1.27-mm pitch. The package supports reflow soldering and provides thermal impedance of 46°C/W (θ_JA).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74ACT7808-20FN, SN74ACT7804-20FN offers identical interface and timing in a smaller memory footprint, while 7203L15TPG provides equivalent capacity in a different package with inverted flag polarity - both require validation of reset behavior, expansion compatibility, and thermal performance under same operating conditions.

Availability

SN74ACT7808-20FN is available at Aetrix Electronics and suitable for telecom line interface buffering, industrial PLC data acquisition, legacy backplane data bridging, and test equipment pattern generation requiring stable component supply across long-lifecycle programs.

Supply support for SN74ACT7808-20FN 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 U.S.-based semiconductor company founded in 1930, specializing in analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.

The SN74ACT7808-20FN belongs to TI's 74ACT advanced CMOS logic family, engineered for high-speed, low-noise FIFO buffering in systems requiring deterministic data flow control between asynchronous clock domains.

FAQ

What is the maximum data rate supported by the SN74ACT7808-20FN?

The SN74ACT7808-20FN supports a maximum data rate of 50 MHz, verified under recommended operating conditions (VCC = 4.5 V to 5.5 V, TA = 0°C to 70°C, CL = 50 pF). This rating corresponds to the highest guaranteed clock frequency for both LDCK and UNCK inputs, enabling sustained throughput of 450 Mbps (50 MHz × 9 bits) in bit-parallel mode. The -20 speed grade designation confirms this 50-MHz capability.

How does the programmable AF/AE flag function in the SN74ACT7808-20FN?

The AF/AE flag in the SN74ACT7808-20FN is programmable via D0–D8 and DP9 during reset-initiated setup cycles with PEN = low. It reports high when FIFO contents ≤ X (almost-empty) or ≥ (2048 − Y) (almost-full), where X and Y are independently settable offsets (0–1023). Default values are X = Y = 256. The SN74ACT7808-20FN uses this flag to trigger early read/write throttling before FULL or EMPTY states occur.

Can multiple SN74ACT7808-20FN devices be cascaded for increased depth, and what pins are required?

Yes, the SN74ACT7808-20FN supports unlimited depth cascading using dedicated expansion pins: CASEN must be tied low on all cascaded devices, FL must be low on the first device and high on all others, and XO of each device connects to XI of the next. The SN74ACT7808-20FN's on-chip expansion logic eliminates need for external counters or glue logic, preserving timing integrity across the chain.

What is the purpose of the DP9 pin on the SN74ACT7808-20FN?

The DP9 pin on the SN74ACT7808-20FN serves as the most significant bit (MSB) during AF/AE offset programming. When PEN is low and LDCK rises, the 10-bit value formed by D0–D8 and DP9 is latched as either the almost-empty offset (X) or almost-full offset (Y), depending on the number of LDCK transitions. DP9 extends the programmable range beyond 9 bits, allowing X and Y values up to 1023 in the SN74ACT7808-20FN.

Does the SN74ACT7808-20FN require power-on reset, and what happens to outputs during RESET?

Yes, the SN74ACT7808-20FN must be reset upon power-up via the RESET pin. A low-level assertion resets internal stack pointers and sets FULL = high, EMPTY = low, HF = low, and AF/AE = high. Critically, the Q outputs are not driven to defined logic levels during RESET - they remain in their last valid state or float depending on OE status. The SN74ACT7808-20FN relies on external initialization sequencing to ensure deterministic flag and data bus behavior.