Texas Instruments CY74FCT821ATQCT

Overview

CY74FCT821ATQCT from Texas Instruments is a 10-bit positive-edge-triggered bus-interface register with 3-state outputs, designed for high-capacitance load drive (64 mA sink / 32 mA source), TTL-compatible I/O levels, and partial-power-down support via Ioff. It operates at 5 V (4.75–5.25 V), delivers 10 ns propagation delay (tPLH/tPHL), and targets output port buffering in wide data/address buses.

For engineers reviewing the CY74FCT821ATQCT datasheet, CY74FCT821ATQCT pinout, CY74FCT821ATQCT application, or CY74FCT821ATQCT equivalent, key selection criteria include 10-bit parallel register timing, 3-state enable control (OE), edge-rate-controlled noise immunity, Ioff-enabled power-down safety, and QSOP-24 package compatibility with legacy FCT logic families.

Technical Context

This device implements ten independent D-type flip-flops clocked on the low-to-high transition of CP, with synchronous 3-state output control via OE. All inputs accept TTL-level signals (VIL = 0.8 V, VIH = 2.0 V), and outputs drive standard 5-V TTL loads while maintaining CMOS-compatible input thresholds.

Edge-rate control circuitry limits slew rate to reduce simultaneous switching noise; matched rise/fall times ensure clean signal integrity. The Ioff feature disables outputs when VCC = 0 V, blocking reverse current flow during partial power-down-critical for hot-swap and mixed-voltage system designs.

Key Specifications

Pinout & Package

Package: QSOP-24 (DBQ), 0.635 mm pitch, 3.9 mm × 8.7 mm body, RoHS-compliant NIPDAU finish, MSL Level-2-260°C-1 year.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 10-bit bus-interface register applications.

Compared with CY74FCT821BTQCT and CY74FCT821CTQCT, the CY74FCT821ATQCT provides the most balanced trade-off of speed (10 ns), noise immunity (edge-rate control), and power efficiency (0.12 mA/MHz ICCD) for general-purpose 5-V bus interfacing-making it ideal for cost-sensitive industrial and embedded designs where marginal timing headroom is acceptable.

Availability

CY74FCT821ATQCT is available at Aetrix Electronics and suitable for memory address latching, parallel I/O expansion, bus isolation in backplane systems, and TTL-level signal conditioning requiring stable component supply and long-term industrial lifecycle support.

Supply support for CY74FCT821ATQCT 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 delivering analog, embedded processing, and logic solutions with emphasis on reliability, longevity, and industrial-grade performance.

The CY74FCT series was engineered specifically for 5-V TTL-compatible bus interface applications demanding high drive strength, noise immunity, and partial-power-down safety-targeting industrial control, telecom infrastructure, and legacy system upgrades.

FAQ

What is the maximum clock frequency supported by CY74FCT821ATQCT?

The CY74FCT821ATQCT does not specify a maximum clock frequency in its datasheet; instead, timing is defined by minimum pulse width (tw = 7 ns) and setup/hold times (tsu = 4 ns, th = 2 ns). For reliable operation with CL = 50 pF, the practical maximum clock rate is approximately 100 MHz, assuming sufficient board-level timing margin for routing delays and jitter. The CY74FCT821ATQCT is optimized for deterministic edge-triggered latching-not continuous high-speed toggling.

Does CY74FCT821ATQCT support mixed-voltage operation (e.g., 3.3-V inputs)?

No, CY74FCT821ATQCT is strictly a 5-V device with TTL-compatible input thresholds (VIH = 2.0 V min, VIL = 0.8 V max) and requires VCC = 4.75–5.25 V. It does not tolerate 3.3-V-only signaling: inputs below 2.0 V may not register as logic high, and 3.3-V outputs lack sufficient noise margin. For mixed-voltage systems, level translation or a 3.3-V-compatible register (e.g., SN74LVC821A) must be used alongside CY74FCT821ATQCT.

How does the Ioff feature function in CY74FCT821ATQCT during partial power-down?

In CY74FCT821ATQCT, the Ioff circuitry activates when VCC = 0 V, limiting output leakage to ±1 µA even if up to 4.5 V is applied to Y pins. This prevents damaging reverse current from powered bus segments into unpowered sections-enabling safe hot-swap in modular systems. Ioff is automatic and requires no external control; OE and CP inputs remain high-impedance during power-down, preserving isolation integrity.

Can CY74FCT821ATQCT drive a 50-pF, 500-Ω load as specified in the timing tests?

Yes, CY74FCT821ATQCT's timing parameters-including 10 ns tPLH/tPHL and 12 ns tPZH/tPZL-are explicitly characterized under CL = 50 pF and RL = 500 Ω per the JEDEC-standard load circuit. This matches typical PCB trace + receiver input loading. The device maintains full 64 mA sink/32 mA source capability under these conditions, ensuring signal integrity across industrial backplanes and dense motherboard layouts where CY74FCT821ATQCT is commonly deployed.

Is CY74FCT821ATQCT pin-compatible with older 74FCT821 variants like CY74FCT821B or CY74FCT821C?

Yes, CY74FCT821ATQCT shares identical pinout, package footprint (QSOP-24 DBQ), and functional behavior with CY74FCT821BTQCT and CY74FCT821CTQCT. Differences are limited to AC timing specs (propagation delay, setup/hold) and DC drive strength consistency-no PCB layout changes are needed when upgrading or downgrading within the CY74FCT821xTQCT speed grades. All three maintain full logic and thermal compatibility.