Texas Instruments CD74FCT821AEN

Overview

CD74FCT821AEN from Texas Instruments is a BiCMOS 10-bit bus-interface flip-flop with noninverted outputs and 3-state outputs, designed for driving highly capacitive or low-impedance loads in wide data/address buses with parity. It operates from 4.75 V to 5.25 V, supports 70 MHz clock frequency, delivers 48 mA sink current per output, and features controlled edge rates to suppress EMI.

For engineers reviewing the CD74FCT821AEN datasheet, CD74FCT821AEN pinout, CD74FCT821AEN application, or CD74FCT821AEN equivalent, key selection considerations include its 24-pin PDIP (EN) package, TTL-compatible input thresholds (VIH = 2 V, VIL = 0.8 V), 7.5 ns typical propagation delay, 3.7 V max output swing, and SCR latch-up resistance for robust industrial bus interfacing.

Technical Context

The CD74FCT821AEN implements synchronous 10-bit latching on CLK rising edge with independent OE-controlled 3-state output enable. Its BiCMOS output stage combines bipolar and CMOS transistors to limit VOH to ~3.7 V (two diode drops below VCC), reducing VCC/ground bounce and EMI during simultaneous switching.

Input isolation from VCC, buffered control inputs, and undershoot-protection circuitry ensure stable operation under heavy capacitive loading. The device is characterized for 0°C to 70°C operation and complies with TTL logic thresholds while delivering CMOS-level quiescent power efficiency.

Key Specifications

Pinout & Package

CD74FCT821AEN uses a 24-pin plastic dual in-line package (PDIP-24, EN suffix), with 0.3-inch body width and standard through-hole mounting. Pin 1 is top-left corner (notch-down orientation).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar bus-interface flip-flop applications.

Compared with SN74FCT821ATPWR and 74AC16374PC, the CD74FCT821AEN offers unique value in legacy 5 V systems requiring TTL-compatible timing, 10-bit parity-aware buffering, and proven EMI suppression via its 3.7 V output clamp - making it irreplaceable where backward compatibility and signal integrity are jointly critical.

Availability

CD74FCT821AEN is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy computer I/O expansion, and test equipment data capture requiring stable component supply and long-term obsolescence management.

Supply support for CD74FCT821AEN 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 CD74FCT821AEN belongs to TI's FCT logic family - engineered for high-speed, low-noise 5 V bus interfacing with BiCMOS process advantages, targeting legacy system upgrades and EMI-sensitive instrumentation.

FAQ

What is the maximum clock frequency supported by the CD74FCT821AEN?

The CD74FCT821AEN supports a maximum clock frequency of 70 MHz under recommended operating conditions (VCC = 4.75 V to 5.25 V, TA = 0°C to 70°C). This is validated by timing parameters including 7 ns minimum clock pulse width and 4 ns setup time, ensuring reliable data capture in high-speed parallel bus applications. The CD74FCT821AEN maintains this performance across its full commercial temperature range.

Does the CD74FCT821AEN have built-in ESD or latch-up protection?

Yes, the CD74FCT821AEN uses an SCR latch-up-resistant BiCMOS process and circuit design, tested per JEDEC standards to withstand latch-up events under normal operating conditions. It also includes undershoot-protection circuitry limiting output voltage to ≥ −0.5 V, enhancing robustness against transient coupling. The CD74FCT821AEN meets industry-standard ESD immunity requirements for commercial logic devices.

Can the CD74FCT821AEN be used in mixed-voltage systems with 3.3 V logic?

No - the CD74FCT821AEN is specified only for 4.75 V to 5.25 V operation and features TTL-compatible input thresholds (VIH = 2 V, VIL = 0.8 V). Its 3.7 V output swing is optimized for 5 V bus termination and may not reliably drive 3.3 V CMOS inputs without level-shifting. For mixed-voltage use, the CD74FCT821AEN requires external translation or should be replaced with a dual-supply logic family.

What is the purpose of the 3.7 V output voltage limit in the CD74FCT821AEN?

The 3.7 V output high limit in the CD74FCT821AEN results from its BiCMOS output stage clamping VOH to two diode drops below VCC (≈5 V), directly reducing power-bus ringing, VCC bounce, and ground bounce during simultaneous switching. This design choice lowers EMI emissions and improves signal integrity on long or heavily loaded PCB traces - a key advantage of the CD74FCT821AEN in noise-sensitive instrumentation.

Is the CD74FCT821AEN pin-compatible with other FCT-series 10-bit flip-flops?

Yes - the CD74FCT821AEN shares identical pinout and function with CD74FCT821AM (SOIC-24) and CD74FCT821AT (TSSOP-24), differing only in package type and thermal characteristics. All variants use the same logic diagram, timing behavior, and electrical specifications. However, the CD74FCT821AEN is not pin-compatible with non-FCT families such as AC or HC series due to differing output drive architecture and voltage thresholds.