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TPS40303: BP PIN short to BOOT PIN

Part Number: TPS40303

Hi Team,

  My customer reported an issue that BP PIN short to BOOT PIN while using the TPS40303, this issue happened especially doing the output short test: 

  Could you kindly help on below items?

  1) Could you kindly share bootstrap diode electrical characters?

  2) As the datasheet recommend an external Schottky diode,  could you kindly recommend a suitable diode?  what' would happened if using normal diode?


Expect for your kindly support, thanks.

Best Regards


  • Hi

       The bootstrap diode has a typical forward voltage of 0.8V at 5mA of Iboot. This is given in the datasheet table on page 6.

    The purpose of the schottky diode is to minimize the forward drop across the diode. This will give a higher gate drive voltage and hence better Rdson and rise times and hence between efficiencies.

    Can you please let us know how the BP pin to BOOT short happened? Is the failure happening on 1 device or in the design in general?




    Do you have the customer's schematic?

    Do you have voltage waveforms of the switching node during normal full load operation and output short circuit testing?

    Typically a BOOT to BP short results due to excessive switch node voltage over-stressing the reverse breakdown of the of the BP to BOOT diode.  An over current event maximizes the current in the switching FETs, which can produce very high peak switch node voltages.

    Excessive forward current would generally result in the fusing of the metal around the diode, creating an open BP to BOOT condition rather than a short.

    The BP to BOOT "diode" is actually a MOSFET that is driven by the same control signal as the low-side FET, it's body diode is from BP to BOOT, but the channel is turned on during the low-side FET on-time to minimize the BP to BOOT drop and maximize the high-side FET drive voltage.  When VIN is 5V or less, an external Schottky diode can help reduce the BP to BOOT drop and maximize the high-side drive voltage.

    Above 6V, the diode is generally not needed, and if the SW voltage that the boot capacitor is connected to rings negative when the high-side FET is turned off and before the low-side FET is turned on, it is possible to over-charge the boot capacitor. When that occurs, we typically see a BOOT to SW short.

    Using a standard silicon diode generally does not have any negative effects, but it does provide less benefit than using a low forward drop Schottky.