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LM5145: Estimation of maximum gate resistance

Atsushi Hirai
Expert 4870 points
Part Number: LM5145

Tool/software:

Hi team,

Customer is going to use LM5145 with Toshiba's FET TK8R2E06PL. They want to switch the FET as soft as possible.

Could you estimate the maximum gate resistance for this combination?

https://toshiba.semicon-storage.com/info/docget.jsp?did=55709&prodName=TK8R2E06PL

Best Regards,

  • 0
    TI__Guru 58171 points

    Hello Atsushi 

    You have to increase the gate resistor gradually while monitoring the MOSFET temperature. It is hard to estimate the maximum gate resistor value by calculation. In general, ~ 1-5 ohm gate resistor is used in parallel with a gate diode. 

    -EL  

  • 0 in reply to EricLee
    TI__Expert 4870 points

    Eric-san,

    Customer increased the gate resistor gradually and, the overshoot and ringing were gone by 10ohm.

    If there is no issue about MOSFET temperature, they can go with 10ohm? Or, should they reduce it less than 5ohm and add a series resistor at Cbst, or so?

    BTW, they should not add the gate resistor for low side FET, right?

    Regards,

  • 0 in reply to Atsushi Hirai
    TI__Expert 4870 points

    Eric-san,

    I confirmed their circuitry little more.

    He put 10ohm for both High side and Low side and, put 2.2ohm as Rbst.

    The package of TK8R2E06PL is TO-220 so, he doesn't have thermal issue.

    Is there any concern?

    Regards,

  • +1 in reply to Atsushi Hirai
    TI__Guru 58171 points

    Hello Atsushi

    • If there is no issue about MOSFET temperature, they can go with 10ohm? ==>You also have to check if the dead-time is enough or not. 
    • Should they reduce it less than 5ohm and add a series resistor at Cbst, ==> Nope, gate resistor is better than the BST resistor. 
    • They should not add the gate resistor for low side FET, right ==> You don't need the gate resistor on the low-side if the HO-off to LO- on dead-time is enough. 

    -EL