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THS3201: PowerPAD Electrical Isolation

Part Number: THS3201

Support Path: /Product/Development and troubleshooting/Find key information on a device/Find application notes for a device/

Page 3 of the datasheet for this part indicates under the pin assignments call out under Note A that "If a PowerPAD is used, it is electrically
isolated from the active circuitry".  Electrically isolated implies to me that PowerPAD does not serve as a ground current return path for the chip/die.  In my application I'm using the DGN package and for this package there are no pins assigned to ground.  So my question is if the PowerPAD does not serve as the ground return path since as indicated it is electrically isolated how can the THS-3201 operate without an assigned ground pin?  I'm guessing that the ground pad is not electrically isolated as indicated, but I wanted confirmation this as I try to troubleshoot a design using this part.

  • Hi Mike,

    The THS3201 is built on an SOI, where the active circuitry is electrically isolated from the support wafer (bottom of die) by a buried oxide (SiO2) layer (called BOX). In assembly, the die is attached to the thermal pad with conductive epoxy, which makes an ohmic connection to the support wafer, but not to the active circuitry. There is no electrical connection to any voltage or to the active circuitry of the device. Thus in theory the device can connect the power pad to any voltage as long as it does not break down the BOX; to be safe, we specify the power supply rails as the limits. In general we recommend to attach to the ground plane for best thermal performance because the ground plane is usually the largest most contiguous metal plane on most board. The concern is thermal performance, not electrical performance.

    I think the THS3201 has inherent oscillation issues and is not recommended for new designs, maybe something you are trying to debug. I would recommend to switch over to a similar device in our portfolio.

    Best Regards,