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TPS22968: Voltage rating of capacitors connected to CT pins

Part Number: TPS22968

Page 16 of the datasheet states that the capacitors connected between CT and GND must be rated for 25V or higher.  I understand there is a charge pump in this device, but this seems a bit excessive- please confirm.

Also, if this is truly the case, it would be very helpful if the data sheet were much more explicit about this requirement instead of burying it in a paragraph halfway through the data sheet.

Thanks, Best, Steve

  • Hi Steve,

    Thanks for reaching out on E2E.

    In some of our devices, the charge pump can be a 2X/3X pump in order to correctly bias the gate of the FET. In these scenarios, the CT capacitance should be large enough so that there isn't any derating at these higher voltages. Therefore, we usually recommend a CT cap rating of at least 25V or higher.

    Thanks,

    Arthur Huang

  • Understood.  Please, please, PLEASE put this recommendation in an obvious place, like the Pin Functions table:

    I had a 16V rated capacitor in this position, and an astute reviewer managed to catch this before we released the board. 

    It is not good to have such an important piece of information so far back in the data sheet.

    Also, unless you also specify the dielectric of these capacitors, you really don't have any idea how much capacitance is here. 
    I'm dealing with an "X5R" 25V capacitor on this project at the moment that loses 50% of its capacitance with only 5V of bias.