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LM74930-Q1: Powering VS from separate supply at 12V to keep IC always ON for a 48V syste,

Daniel Zmood
Prodigy 10 points
Part Number: LM74930-Q1
Other Parts Discussed in Thread: LM74930

Tool/software:

HI 

  • Our design is for a 48V input system which is hot-swappable 
  • We want to keep the LM74930 IC alive even when there is no source to the MOSFETS so we supply intend to supply it from a fixed 12V supply which is always ON
  • The functional block diagram indicates as illustrated below that the HGATE gate driver is referenced internally to the OUT pin with the CAP pin voltage added to provide the gate enable voltage.
  • My understanding is that it will generate the necessary gate voltage of 60V even if the VS is supplied from fixed voltage of 12V

Please confirm, that we can operate the IC in this manner.

  • 0
    TI__Mastermind 47695 points

    Hi Daniel,

    Applying external VS of 12V is not recommended.

    Also, VCAP will be driven to VS+12V always. Hence when 48V is applied, VCAP will still be ~24V and hence wont turn on the FETs.

    Regards,

    Shiven Dhir

  • 0 in reply to Shiven Dhir
    Prodigy 10 points

    Hi Shiven,

    Firstly, thanks that clarifies the behaviour.

    However, the datasheet is mis-leading as it indicates that the charge pump capacitor is referenced to the OUT node of the terminal quite clearly in the datasheet block diagram as I highlighted. We wanted to be able to keep the IC & bootstrap capacitor active and enabled even if the source supply is removed and replaced.