UCC5686PM

Overview

The UCC5686PM is a 27-line active terminator for low-voltage-differential (LVD) SCSI networks, designed to comply with Ultra2, Ultra3, Ultra160, and Ultra320 specifications. It operates on a single supply voltage ranging from 2.7 V to 5.25 V. The device features a typical channel capacitance of 2 pF and a differential impedance of 105 Ω. It includes an internal 1.25-V regulator and a 1.3-V DIFSENS output. The component is housed in a 64-pin low-profile QFP package and supports an operating temperature range of 0°C to 70°C.

Feature Summary

• Active Y-terminator design improves frequency response for LVD SCSI buses.
• Built-in SPI-3 mode with change/filter delay functionality.
• Differential failsafe bias ensures stable operation during signal transitions.
• Low channel capacitance minimizes bus loading for maximum peripheral support.

Applications

• Ultra2 SCSI network termination
• Ultra3 SCSI network termination
• Ultra160 SCSI network termination
• Ultra320 SCSI network termination

Procurement Notes

Verify the specific ordering suffix against the manufacturer's current documentation before purchase. Confirm that the PM package designation corresponds to the required 64-pin low-profile QFP form factor. Ensure the component meets the specified commercial temperature range requirements for your target application environment.

Selection Notes

Select this component when designing systems requiring compliance with multiple generations of LVD SCSI standards. The integrated regulator simplifies power distribution compared to discrete solutions. Verify that the host system provides the necessary 2.7 V to 5.25 V supply rails and that the PCB layout accommodates the 64-pin QFP footprint constraints.

Part Context

This part belongs to the UCC568x family of SCSI terminators manufactured by Texas Instruments. It serves as a migration path for upgrading legacy SCSI systems to higher speed standards without redesigning the termination circuitry. The device is distinct from the UCC5687, which utilizes different disconnect pin configurations.

Replacement Considerations

The UCC5687PM is a functional alternative within the same family but requires attention to pin assignments for disconnect control lines. Verify pin compatibility regarding DISCNCT1 and DISCNCT2 locations before substituting.

FAQ

How does the UCC5686 handle mode changes between SE and LVD?

The device uses the DIFFB input pin to detect the connected drive type. A built-in time delay and filter section manages the transition, introducing a mode change delay between 100 ms and 300 ms.

What is the purpose of the REG pin?

The REG pin is the output of the internal 1.25-V regulator. It must be connected to a 4.7-µF bypass capacitor and a high-frequency, low-ESR 0.01-µF capacitor to ground to ensure stability.

Can this device terminate High-Voltage Differential (HVD) SCSI buses?

No, the UCC5686 is designed exclusively for Low-Voltage Differential (LVD) SCSI networks. Single-ended (SE) and HVD SCSI drivers are not supported.