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LM5116: Max. peak current for gate driver

df_spw
Prodigy 60 points
Part Number: LM5116

Tool/software:

Hello,

I am on the way to optimize the EMI behaviour of our buck converter circuit with the LM5116MH/NOPB controller. The Vin is something between 58V...80V and Vout=48V for Pout: 0W...550W. Unfortunately there is a problem with the external gate resistors we are using for the 1x low side and 2x high side MOSFETs. 

According to the LM5116 datasheet (page 9 & 10) we are allowed  to use the driver source current of  appr. 3.2A for LO and 1.8A for HO and the driver sink current fo 2.9A for HO and 6.8A for LO at the Vcc=12V. 

There is a need to switch off very fast and to switch on a little bit slower to avoid high ringing amplitudes during the switching process. We want to avoid the use of different external gate resistors like the typical application is showing that on page 21 in the datasheet but doesn't that mean, that you will always overdrive the LM5116 internal gate driver with the peak gate currents of Q1 & Q2 (Si7850) ?

Maybe there is an explanation for driving external switch MOSFETs without adding the gate resistors that I do not know?

 

Best regards

 

Dirk.

  • 0
    TI__Genius 13996 points

    Hello Dirk

    Even in typical application circuit MOSFETs are driven without gate resistors. It is absolutely to drive the FETs without gate resistors if application, layout and FETs allows that.  

    Hope this helps. Let me know if need any clarification or further help.

    Thank you

    Regards

    Onkar Bhakare

  • 0 in reply to Onkar Bhakare
    TI__Genius 13996 points

    Hello Dirk

    Let me know if need further help. Kindly close the thread if you feel your query has been resolved.

    Thank you

    Regards

    Onkar Bhakare

  • 0 in reply to Onkar Bhakare
    Prodigy 60 points

    Hello Onkar,

    thanks for your help. If I am going to choose the 0 Ohm gate resistors, I will surely overdrive the driver output for a short time due to the fact that there is a MOSFET gate capacitance with a small internal gate resistance of 1...2Ohm. That means at a Vcc=12V the driver has to deliver 6A...12A and this will be definitely out of spec or do you have a more detailed eplaination that issue ?

  • 0 in reply to df_spw
    TI__Genius 13996 points

    Hello Dirk

    Device would limit current mentioned in the following EC table. I would ensure, current would remain within this spec. So even if short Rg by 0 ohm peak current would be limited by device

    Hope this helps

    Thank you

    Regards

    Onkar Bhakare

  • +1 in reply to Onkar Bhakare
    Prodigy 60 points

    Hello Onkar,

    thank you. This was the information that I was looking for.

    Best regards

    Dirk.