Renesas 74FCT621TSOG8

Overview

74FCT621TSOG8 from Renesas Electronics (formerly IDT) is an octal bus transceiver with open-drain outputs in both A→B and B→A directions, designed for asynchronous bidirectional data bus interfacing in industrial systems. It operates over –40°C to +85°C, supports 5V ±5% supply, delivers 64mA sink capability on B-bus outputs, and features true TTL-compatible inputs/outputs (VIH = 2V min, VOL = 0.55V max at 64mA).

For engineers reviewing the 74FCT621TSOG8 datasheet, 74FCT621TSOG8 pinout, 74FCT621TSOG8 application, or 74FCT621TSOG8 equivalent, key selection considerations include open-drain bidirectional drive strength, live-insertion support via power-off disable, JEDEC 18 compliance, and SOIC-20 package compatibility with legacy FCT logic designs.

Technical Context

The 74FCT621TSOG8 implements dual-directional, non-inverting open-drain transceivers with independent GBA (B-to-A enable) and GAB (A-to-B enable) controls. Its function table allows simultaneous or selective direction control - including OFF state when both enables are high - enabling flexible timing in mixed-voltage or wired-OR bus architectures.

It uses Fast CMOS process technology to achieve propagation delays as low as 1.5ns (tPHL, B→A), with guaranteed max 13ns tPLH across industrial temperature range. Output clamping diodes (VIK = –1.2V) and ±1µA input leakage ensure robustness during hot-swap and bus contention scenarios.

Key Specifications

Pinout & Package

74FCT621TSOG8 is housed in a 20-pin Small Outline IC (SOIC) package, 7.5mm body width, with standard 0.050" (1.27mm) lead pitch and gull-wing leads. Pin 1 marked by notch or dot; pin 10 = GND, pin 20 = VCC.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar octal open-drain bus transceiver applications.

Compared with SN74F245N and 74ACT16245QG, the 74FCT621TSOG8 uniquely combines open-drain bidirectionality, 64mA B-bus drive, and guaranteed power-off high-Z - making it the only option among the three qualified for industrial backplane hot-swap and wired-OR arbitration.

Availability

74FCT621TSOG8 is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy bus extensions, and programmable logic I/O expansion requiring stable component supply, long-lifecycle availability, and RoHS-compliant SOIC packaging.

Supply support for 74FCT621TSOG8 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

Renesas Electronics Corporation is a global semiconductor leader delivering microcontrollers, analog, power, and connectivity solutions for automotive, industrial, infrastructure, and IoT applications.

The 74FCT621TSOG8 belongs to Renesas' legacy IDT Fast CMOS logic family, engineered specifically for robust, low-power, high-speed 5V bus interfacing in industrial control and communications equipment.

FAQ

What is the maximum sink current supported by each B-bus output of the 74FCT621TSOG8?

Each B-bus output (B1–B8) of the 74FCT621TSOG8 supports a maximum DC sink current of 64mA under industrial conditions (VCC = 4.75V, TA = +85°C). This is specified in the DC Electrical Characteristics table and enables direct driving of multiple TTL inputs or long PCB traces without external buffers. The 74FCT621TSOG8 maintains this rating across its full operating temperature range.

Does the 74FCT621TSOG8 support live insertion, and how is that implemented?

Yes, the 74FCT621TSOG8 supports live insertion via power-off disable functionality: when VCC = 0V, all outputs enter high-impedance state regardless of input levels or enable states. This is enabled by internal circuitry that disconnects I/O paths during power loss, preventing bus contention. The 74FCT621TSOG8 datasheet explicitly confirms this behavior under "Power Off Disable Outputs" in the Features section.

What is the difference between the A-bus and B-bus output drive capability in the 74FCT621TSOG8?

The B-bus outputs (B1–B8) of the 74FCT621TSOG8 are rated for 64mA sink current, while the A-bus outputs (A1–A8) are rated for 48mA. This asymmetry is documented in the DC Electrical Characteristics table under separate VOL specifications. The 74FCT621TSOG8 uses this design to optimize drive strength where higher loading occurs (typically on the system-side B bus), while conserving power on the controller-side A bus.

Is the 74FCT621TSOG8 pin-compatible with earlier IDT FCT621 variants like the 74FCT621TQG?

No - the 74FCT621TSOG8 uses a 20-pin SOIC package (SOIC-20), whereas the 74FCT621TQG is a 24-pin QSOP. Pin count, pitch, and physical dimensions differ; no pin-to-pin compatibility exists. The 74FCT621TSOG8 shares identical pinout and function with other SOIC-20 variants (e.g., 74FCT621TSO), but not with QSOP or TSSOP versions. Always verify package code before PCB layout.

What JEDEC standard does the 74FCT621TSOG8 comply with, and why does it matter?

The 74FCT621TSOG8 meets or exceeds JEDEC Standard 18, which defines electrical, switching, and mechanical requirements for advanced CMOS logic devices. Compliance ensures interoperability with other JEDEC-18-compliant components - critical for system-level timing predictability, noise immunity, and bus signal integrity in industrial designs. This specification is explicitly stated in the Features section of the 74FCT621TSOG8 datasheet.