Texas Instruments SN74ACT2235-20FN

Overview

SN74ACT2235-20FN from Texas Instruments is an asynchronous bidirectional first-in, first-out (FIFO) memory IC comprising two independent 1024 × 9-bit FIFOs for high-speed data buffering between mismatched clock domains. It delivers 25 ns access time with 50-pF load, supports up to 50 MHz data rates, and integrates programmable almost-full/almost-empty flags for precise buffer management in bus arbitration systems.

For engineers reviewing the SN74ACT2235-20FN datasheet, SN74ACT2235-20FN pinout, SN74ACT2235-20FN application, or SN74ACT2235-20FN equivalent, key selection criteria include dual-asynchronous operation, 44-pin PLCC (FN) package compatibility, 5 V supply tolerance, independent reset and clock control per FIFO, and direct TTL/CMOS bus interface capability without external level-shifting.

Technical Context

The SN74ACT2235-20FN implements two physically separate 1024-word × 9-bit FIFO arrays with fully independent write (LDCKA/LDCKB) and read (UNCKA/UNCKB) clocks, enabling true asynchronous data transfer across clock domains. Each FIFO features dedicated empty/full/half-full status flags and user-programmable almost-full/almost-empty offsets via DAF/DBF inputs.

Its integrated bus transceiver architecture-controlled by GAB/GBA enables and SAB/SBA select inputs-supports eight distinct bus-management functions including real-time pass-through, FIFO-to-bus, bus-to-FIFO, and bidirectional stored-data routing without external logic. The device uses Advanced CMOS (ACT) technology for low power consumption and high output drive (–8 mA VOH, 16 mA VOL on I/O ports).

Key Specifications

Pinout & Package

SN74ACT2235-20FN is housed in a 44-pin plastic leaded chip carrier (PLCC, FN package), JEDEC MS-018 compliant, with 0.050-inch lead pitch and gull-wing J-leads. Thermal impedance θ_JA = 46°C/W supports stable operation at full speed under typical PCB layout conditions.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74ACT2235-20PAG, the SN74ACT2235-20FN provides easier manual handling and socket compatibility but requires more board area; versus 7200L15J8, it delivers dual independent FIFOs, built-in bus transceivers, and programmable status flags-making it uniquely suited for complex multi-domain buffering where real-time bus arbitration is required.

Availability

SN74ACT2235-20FN is available at Aetrix Electronics and suitable for industrial automation, legacy bus interfacing, DSP co-processing, and real-time audio buffering requiring stable component supply and long-term obsolescence planning.

Supply support for SN74ACT2235-20FN 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 global semiconductor leader founded in 1930, specializing in analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.

The SN74ACT2235-20FN belongs to TI's legacy Advanced CMOS (ACT) logic family, designed specifically for high-reliability, 5-V asynchronous data buffering in systems requiring deterministic timing and robust bus interface capability.

FAQ

What is the maximum clock frequency supported by SN74ACT2235-20FN for write and read operations?

The SN74ACT2235-20FN supports up to 50 MHz for both LDCKA/LDCKB (write clocks) and UNCKA/UNCKB (read clocks) under recommended operating conditions (VCC = 4.5–5.5 V, TA = 0°C to 70°C). This rating is confirmed in the timing requirements table of the SCAS148F datasheet, where t_CLK min = 20 ns corresponds to 50 MHz. Performance is load-dependent and assumes CL = 50 pF.

How does the programmable almost-full/almost-empty flag work on SN74ACT2235-20FN?

The SN74ACT2235-20FN allows user-defined almost-full/almost-empty thresholds via DAF (for FIFO A) and DBF (for FIFO B). During reset, a low-to-high transition on DAF latches the binary value on A0–A8 as offset X (0–511); AF/AEA then asserts when FIFO A contains ≤X or ≥(1024–X) words. Default X = 256 if DAF remains high during reset. The same mechanism applies to AF/AEB using DBF and B0–B8.

Can SN74ACT2235-20FN operate with a 3.3-V supply?

No, SN74ACT2235-20FN is specified only for 4.5 V to 5.5 V operation per its recommended operating conditions. Its Advanced CMOS (ACT) process requires 5-V rail compliance; applying 3.3 V will result in undefined logic states, insufficient output drive, and potential functional failure. For 3.3-V systems, consider newer families like SN74LV or SN74LVC with compatible FIFO functionality.

What are the thermal characteristics of the SN74ACT2235-20FN in its FN package?

The SN74ACT2235-20FN in the 44-pin PLCC (FN) package has a junction-to-ambient thermal resistance (θ_JA) of 46°C/W, as specified in the absolute maximum ratings section. This value assumes standard JEDEC test board conditions. At maximum ICC (400 µA) and worst-case ambient (70°C), junction temperature remains well below the 150°C limit, supporting reliable operation in commercial environments without forced airflow.

Does SN74ACT2235-20FN require external pull-up resistors on its status flag outputs?

Yes, SN74ACT2235-20FN's status flag outputs-including AF/AEA, AF/AEB, EMPTYA, EMPTYB, FULLA, FULLB, HFA, and HFB-are open-drain and require external pull-up resistors to VCC (typically 4.7 kΩ–10 kΩ) to generate valid logic-high levels. This is explicitly stated in the Terminal Functions table and confirmed by the logic diagram showing flag outputs connected to VCC via external resistors in application schematics.