Diodes Incorporated PI74FCT646ATQ

Overview

PI74FCT646ATQ from Pericom Semiconductor is a fast CMOS octal registered transceiver with non-inverting data path, 3-state D-type flip-flops, and dual-bus bidirectional control via DIR and G pins. It features integrated 25Ω series output resistors, TTL-compatible I/O, –40°C to +85°C operation, and real-time/stored data multiplexing for bus isolation in backplane or memory interface applications.

For engineers reviewing the PI74FCT646ATQ datasheet, PI74FCT646ATQ pinout, PI74FCT646ATQ application, or PI74FCT646ATQ equivalent, key selection criteria include propagation delay (≤4.8 ns), output enable/disable timing (tPZH ≤7.3 ns, tPHZ ≤6.3 ns), 25Ω on-die termination, and compatibility with FAST™-series pinouts for drop-in speed/power upgrades.

Technical Context

The PI74FCT646ATQ implements an octal bidirectional transceiver with internal A/B register storage, controlled by DIR (direction) and G (output enable) signals. Real-time or stored data transfer is selected via SAB/SBA inputs, eliminating multiplexer glitches during mode transitions.

Its 25Ω series output resistors suppress signal reflections without external termination, while hysteresis on all inputs improves noise immunity. The device operates at 5.0V ±5% and supports simultaneous clocking of both registers only when select control is low.

Key Specifications

Pinout & Package

PI74FCT646ATQ is housed in a 24-pin TQSOP (Thin Quad Small Outline Package) with 0.65 mm pitch, 3.9 mm body width, and exposed pad for thermal enhancement. Pin numbering follows JEDEC MS-013 standard.

Key Features

Applications

Equivalent & Alternatives

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

Compared with PI74FCT646TQ and SN74FCT646Q, the PI74FCT646ATQ delivers the tightest timing window and eliminates external termination components-making it optimal for new designs prioritizing signal integrity, layout density, and timing headroom.

Availability

PI74FCT646ATQ is available at Aetrix Electronics and suitable for backplane routing, memory interface buffering, legacy bus extension, and industrial I/O module hub applications requiring stable component supply, long-term lifecycle support, and verified industrial temperature performance.

Supply support for PI74FCT646ATQ 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

Pericom Semiconductor was a fabless provider specializing in high-speed interface, timing, and logic solutions, acquired by Diodes Incorporated in 2016. Its FCT logic family targeted performance-critical digital systems before consolidation into Diodes' broader portfolio.

The PI74FCT646ATQ belongs to the PI74FCT2XXX advanced CMOS logic product line, designed specifically for noise-sensitive, high-density digital systems needing fast, low-power, and reflection-free bus interfacing in industrial and telecom infrastructure.

FAQ

What is the function of the SAB and SBA pins on the PI74FCT646ATQ?

SAB and SBA are data source select inputs that determine whether each bus receives real-time or stored register data. A low level on SAB selects real-time data from bus B to bus A; a high level selects stored data from Register B. Similarly, SBA controls data source for bus B. This dual-select architecture prevents glitches during mode transitions and enables flexible data routing without external logic.

Does the PI74FCT646ATQ require external termination resistors?

No. The PI74FCT646ATQ integrates a 25Ω series resistor on every output, matching common PCB trace impedances and suppressing reflections. This eliminates the need for discrete 25Ω resistors in series with each output line-reducing component count, board area, and potential impedance mismatches introduced by parasitic inductance in discrete placements.

How does the PI74FCT646ATQ differ from the PI74FCT648ATQ?

The PI74FCT646ATQ is a non-inverting transceiver, while the PI74FCT648ATQ is its inverting counterpart. Both share identical pinout, timing, and control logic (DIR/G/SAB/SBA), but the 648ATQ inverts data during transfer. This functional difference dictates usage: 646ATQ preserves logic polarity for direct bus mirroring; 648ATQ suits applications requiring inversion, such as differential signaling interfaces or specific protocol framing.

Can the PI74FCT646ATQ operate at 3.3 V?

No. The PI74FCT646ATQ is specified only for 5.0 V ±5% operation (4.75–5.25 V). Its TTL-compatible input thresholds (VIH = 2.0 V, VIL = 0.8 V) and internal circuitry are optimized for 5 V rail operation. Applying 3.3 V may result in unreliable logic levels, increased propagation delay, or failure to meet AC specifications-including output drive strength and timing margins.