onsemi 74F646SPC

Overview

74F646SPC from Fairchild Semiconductor is an octal transceiver/register with 3-STATE outputs, designed for bidirectional data bus interfacing between two 8-bit buses (A and B). It features independent A/B registers, non-inverting data paths, clock-controlled storage, and direction-selectable real-time or stored-data transmission. It operates at 5 V, supports up to 90 MHz clock frequency, and is rated for 0°C to +70°C ambient temperature.

For engineers reviewing the 74F646SPC datasheet, pinout, applications, or equivalent options, key selection considerations include its dual-register architecture, 3-STATE output drive capability (−12 mA/64 mA), isolation mode operation, and compatibility with standard 74F logic timing and voltage thresholds.

Technical Context

The 74F646SPC integrates eight D-type flip-flops per bus (A and B), enabling synchronous latching of data on rising clock edges at CPAB or CPBA. Its control logic uses active-low G (output enable) and DIR (direction) inputs to select real-time (transparent) or stored-mode transfer between buses.

It supports multiplexed operation via SAB/SBA select inputs, allowing simultaneous use of live bus data and registered data in a single cycle. All I/O pins are 3-STATE capable with defined leakage, clamp diode, and short-circuit current limits per JEDEC-compliant 74F specifications.

Key Specifications

Pinout & Package

74F646SPC is housed in a 24-lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001 compliant, 0.300" wide, with through-hole mounting and standard 0.1" pin pitch.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar octal transceiver/register applications.

Compared with 74F645SC and 74F648SPC, the 74F646SPC uniquely provides non-inverting, clock-synchronized register storage on both buses - essential for deterministic data staging in multi-cycle bus protocols where polarity preservation and timing predictability are required.

Availability

74F646SPC is available at Aetrix Electronics and suitable for backplane routing, microprocessor bus expansion, and digital test equipment requiring stable component supply and long-term obsolescence management.

Supply support for 74F646SPC 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

Fairchild Semiconductor was a U.S.-based designer and manufacturer of analog and mixed-signal semiconductors, acquired by ON Semiconductor in 2016; its legacy 74F logic family remains widely deployed in industrial and legacy systems.

The 74F646SPC belongs to Fairchild's 74F Fast TTL logic product line, engineered for high-speed, low-power bus interface applications in commercial-grade computing and control systems.

FAQ

What is the operating voltage range for the 74F646SPC?

The 74F646SPC operates over a supply voltage range of +4.5 V to +5.5 V. This range ensures compatibility with standard 5 V TTL systems while maintaining adequate noise margins. The device is not rated for operation outside this window, and applying voltages below 4.5 V may result in unreliable logic thresholds or increased propagation delay. Always reference the absolute maximum rating of −0.5 V to +7.0 V for transient conditions only.

Does the 74F646SPC support true bidirectional data flow between A and B buses?

Yes, the 74F646SPC supports full bidirectional data flow via the DIR input: when DIR = HIGH, data flows A→B; when DIR = LOW, data flows B→A. This applies in both transparent (real-time) and stored (register-based) modes. The G input independently controls 3-STATE output enable/disable, allowing complete bus isolation regardless of direction setting - a key feature distinguishing 74F646SPC from simpler transceivers.

How does the 74F646SPC handle clocking for register updates?

The 74F646SPC uses two dedicated edge-triggered clock inputs: CPAB clocks data from the B bus into the A register, and CPBA clocks data from the A bus into the B register. Both respond to the LOW-to-HIGH transition. Data is latched synchronously on each rising edge, and register updates occur independently - enabling simultaneous capture from both buses without conflict or arbitration logic.

What is the maximum fan-out capability of the 74F646SPC outputs?

The 74F646SPC outputs support a fan-out of 600/106.6 (80) for HIGH/LOW states - meaning each output can drive up to 600 standard 74F inputs in the HIGH state and up to 106.6 (or 80, per typical loading convention) in the LOW state. This high fan-out is achieved through robust output drive strength (−12 mA/64 mA) and is validated under CL = 50 pF and VCC = 5.0 V conditions specified in the AC Electrical Characteristics table.

Can the 74F646SPC be used in systems requiring extended temperature operation?

No - the 74F646SPC is rated for 0°C to +70°C ambient temperature only. While its absolute maximum junction temperature is +150°C, the recommended operating conditions explicitly limit ambient use to the commercial grade range. For industrial or automotive applications requiring −40°C to +85°C or wider, alternative solutions such as 74ACT or modern CMOS equivalents must be evaluated - the 74F646SPC itself is not characterized or guaranteed beyond 0°C to +70°C.