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DRV8711: External FET selection

Part Number: DRV8711
Other Parts Discussed in Thread: CSD18531Q5A

Hello,

  We are planning to use DRV8711 with a motor whose rated current is not more than 2A per phase. We find that the rating of FET(CSD18531Q5A) present in the evaluation board of DRV8711 very highly rated for our application.

  Shall we choose a lower rated FET

We have these doubts while  choosing a  lower rated FET

  1. Can we choose VDSSBR as 30V instead of 60V

  2. Should we consider only continuous drain current value alone or we should consider SOA curve also.

Please advise us thank you

 

  • Diwakar,

    Yes. you can select a lower rated FET to optimize the BOM cost.

    1. You can choose 30V FET if the VM voltage spike always lower than 30V. Please check VM voltage spike carefully in all operation cases. such as: load transient, input transient; motor back drive...

    2. Consider both: SOA and  thermal performance.

  • Hi Wang,

       We have a supply voltage of 24V , So we think it is better to go with 60 V. But we have problem with SOA curve. We are not sure about our expected current pulse frequency. Is there any thumb rule for determining the worst case current pulse.

  • Hi Diwakar,

    Typically the current pulses are less than the full scale current. There are exceptions to this such as:

    1) An output is shorted to power or ground. This current is limited by the VDS monitor and tblank.

    2) Capacitors are connected to the outputs creating inrush currents during charging and discharging.

    It is recommended to examine the current using a current probe. You will then know the expected current during normal operation.