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DRV8705-Q1: charge pump

Yasushi Fujiwara
Genius 12725 points
Part Number: DRV8705-Q1

Hello Experts,

My customer has question as follows. Would you answer it, please?
1. The datasheet mentioned that the DRV8705-Q1 is not designed to support significant voltage difference between PVDD and DRAIN. Customer would like to know what is significant voltage difference between PVDD and DRAIN.


2. Also customer would like to why significant voltage difference between PVDD and DRAIN cannot permit.

Best Regards,
Fujiwara

  • 0
    TI__Mastermind 44855 points

    Hi,

    Thank you for your questions. Your colleague also posted same question recently. Appreciated if you try to avoid such a duplication from next time.

      Actually, this sentence is mixed with two topics.

    - This charge pump's cap bottom side is connected to PVDD, not GND.  Some charge pump in the market has the output cap-GND configuration, but this DRV's cap is not.

    -Normally PVDD, VBAT(Battery 12V supply) and DRAIN is connected. However, some customer may have slightly different voltage rail on these by separating them. Although slightly different, those voltage levels are normally similar while motor driving operation. Therefore no limitation happens.

    If PVDD is much lower than DRAIN, DRV cannot drive external high side FET. This is limitation.

    For example, PVDD=8V and DRAIN is 30V, DRV need to provide 30V+~10V to turn on High side FET. However, charge pump output can provide PVDD+~10.5V only.

    Mostly this situation should not happen in automotive application, therefore mostly nobody care much for this limitation.

    regards

    Shinya Morita

    regards

    Shinya Morita