Texas Instruments CY74FCT821CTSOCT

Overview

CY74FCT821CTSOCT 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 I_off. It operates at 5 V (4.75–5.25 V), delivers 6 ns propagation delay (t_PLH/t_PHL) at 50 pF, and is used in address/data bus buffering for industrial control backplanes.

For engineers reviewing the CY74FCT821CTSOCT datasheet, CY74FCT821CTSOCT pinout, CY74FCT821CTSOCT application, or CY74FCT821CTSOCT equivalent, key selection criteria include 24-pin SOIC package compatibility, edge-rate controlled noise immunity, I_off-enabled power-down isolation, matched rise/fall times, and FCT-family functional interchangeability with AM29821 and CY74FCT374 derivatives.

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. Its output drivers feature edge-rate control circuitry to reduce simultaneous switching noise and ensure matched t_r/t_f (typical 3.5 ns).

The I_off specification enables safe partial-power-down operation: when V_CC = 0 V, leakage current is limited to ±1 µA per I/O terminal, preventing backflow damage. Inputs tolerate 7 V absolute max, and outputs are fully TTL-compatible-VIH = 2 V min, VOL = 0.55 V max at 64 mA sink.

Key Specifications

Pinout & Package

Package: 24-pin SOIC (DW), 7.5 mm × 15.4 mm body, 1.27 mm pitch, RoHS-compliant NiPdAu finish, MSL Level-1.

Key Features

Applications

Equivalent & Alternatives

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

Compared with CY74FCT821BTSOCT, the CY74FCT821CTSOCT delivers 25% faster timing for high-throughput bus cycles; versus SN74FCT821CTSOCT, it shares identical electrical behavior and layout compatibility, differing only in part-number branding lineage.

Availability

CY74FCT821CTSOCT is available at Aetrix Electronics and suitable for industrial backplane buffering, legacy system address expansion, test equipment signal conditioning, automated test fixture interface, and embedded control I/O consolidation requiring stable component supply and long-term lifecycle assurance.

Supply support for CY74FCT821CTSOCT 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 over 50 years of innovation in high-reliability interface and timing products.

The CY74FCT821CTSOCT belongs to TI's FCT logic family-designed specifically for noise-immune, high-drive 5 V bus interfacing in industrial, telecom, and test equipment where signal integrity and power-down safety are critical.

FAQ

What is the maximum clock frequency supported by CY74FCT821CTSOCT?

The CY74FCT821CTSOCT does not specify a maximum clock frequency in its datasheet; instead, it guarantees timing parameters at defined load conditions. With 6 ns propagation delay and 3 ns setup/hold windows, it reliably supports bus clock rates up to 160 MHz in typical 50 pF loading scenarios. The actual maximum usable frequency depends on board layout, termination, and fanout-designers should verify timing closure using the published t_su = 3 ns and t_h = 1.5 ns values in their specific system.

Does CY74FCT821CTSOCT support mixed-voltage operation (e.g., 3.3 V inputs driving a 5 V device)?

Yes, CY74FCT821CTSOCT accepts 3.3 V logic inputs safely: its VIH minimum is 2.0 V and absolute maximum input voltage is 7 V, making it compatible with 3.3 V CMOS and LVTTL sources. However, its outputs swing to 5 V levels (VOH ≥ 2.4 V at –15 mA), so downstream devices must tolerate 5 V inputs unless level translation is added. No internal level-shifting circuitry is present-the device operates strictly as a 5 V supply rail component.

How does the I_off feature of CY74FCT821CTSOCT protect the system during partial power-down?

The I_off circuitry in CY74FCT821CTSOCT disables all I/O terminals when V_CC = 0 V, limiting leakage current to ±1 µA per pin. This prevents damaging reverse current flow from live buses into a powered-down section-critical during hot-swap operations or staggered power sequencing. Unlike passive pull-ups or diodes, I_off requires no external components and maintains high-impedance isolation across the full –0.5 V to 7 V input voltage range, ensuring bus integrity even with floating or driven inputs.

Can CY74FCT821CTSOCT be used as a direct replacement for CY74FCT374 in existing designs?

Yes-CY74FCT821CTSOCT is explicitly described as a "10-bit-wide buffered version of the popular CY74FCT374 function" and is functionally, electrically, and pinout-compatible with CY74FCT374 in 24-pin SOIC packages. Both share identical CP, OE, D, and Y pin assignments, same 5 V supply range, and matching timing characteristics. No PCB changes are needed; however, note that CY74FCT821CTSOCT provides 10 bits versus CY74FCT374's 8 bits, so unused pins must be handled per design requirements.

What thermal considerations apply to CY74FCT821CTSOCT in continuous 64 mA output operation?

In sustained 64 mA sink operation per output, CY74FCT821CTSOCT's SOIC (DW) package exhibits θ_JA = 46°C/W. At worst-case 5.25 V supply and full 10-bit output loading, total power dissipation may reach ~180 mW, resulting in ~8°C junction-to-ambient rise above ambient. Derating is not required below 85°C ambient, but designers should ensure adequate copper pour and avoid stacking heat-generating components nearby. The device's rated operating range remains –40°C to +85°C under these conditions.