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LM5146-Q1: Query on application

Sandeep Varma
Prodigy 140 points
Part Number: LM5146-Q1
Other Parts Discussed in Thread: LM5146

Hi,

I have queries on LM5146 as mentioned below:

1)  Does gate resistor value impact the functioning of Adaptive dead time control ? Could you please share any documents about the same ? Does higher gate resistor value reduce dead time ?
2) There is neither external bootstrap diode nor bootstrap cap series resistor in ref design of LM5146. Can internal bootstrap diode withstand short high current while charging the  Bootstrap capacitor ?

Thanks,
Sandeep.

  • 0
    TI__Guru 69997 points

    Hi Sandeep,

    The bootstrap diode is internal and shouldn't have any issues with a typical boot cap of 100nF. There is no need for higher boot cap values that may stress the diode at startup when charging the boot cap from 0V.

    In terms of the gate resistor, which is only advised on the high-side FET gate, it may increase the LO off to HO on deadtime (as the HO voltage at the FET is slower). However, the opposite transition should be largely unaffected as the SW voltage going low is sensed. I recommend just putting the resistor in series with the boot cap to limit the high-side turn on. The EVM has a value of 2.2Ω for this resistor.

    Regards,

    Tim

  • 0 in reply to Timothy Hegarty
    Prodigy 140 points

    Hi,
    1)  As i mentioned, do you have any doc to study  for how adaptive dead time works ?
    2)  Will Controller limit the gate current even if Gate resistance is zero with out impacting its reliability? 

  • 0 in reply to Sandeep Varma
    TI__Guru 69997 points

    1) - See description in the datasheet.

    2) - The current in the gate loop is naturally limited by the gate driver Rdson and the FET internal gate resistance. There is no concern from that standpoint.