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LM3150 gate drive capabilities

Geovid Kali
Intellectual 1245 points
Other Parts Discussed in Thread: CSD18502Q5B, LM3150

Hi,

I did a webench design with the LM3150 and noticed that the FETs were only rated at 30V.  My design requires up to 36V.  Can the LM3150 drive higher voltage fets such as the CSD18502Q5B.  Is the 30V a restriction of webench or of the controller?  It also looks like the current never actually goes through the controller.  Does this mean that I can use it in higher current applications (assuming I use the correct FETS and inductors)?  Assuming I can drive larger FETs for higher voltage/current applications, would switching effects become an issue?

Thanks,

Geovid Kali

  • 0
    TI__Expert 3950 points

    Hello Kali,

    you are right about the fact that the current never goes through the controller therefore you can use it for higher current and voltage.

    Anyway the driver capability really depends on the gate charge of the MOSFET you are using and the switching frequency and it does not depends on the rated voltage of the FETs.

    In any case webench should generate a proper design, could you please share it so we can take a look at it and fix the problem?

    Thank you,

    Giuseppe

  • 0 in reply to Giuseppe Pinto
    TI__Intellectual 1245 points

    Hi Giuseppe,

    Thank you for the quick response. 

    Webench only allows for a max of 30V FETs for this device.  I spoke with someone from the webench team and they said that not all of the new FETs are integrated into webench yet.  My questions more relates to the fact that the bigger the FET gets the higher the gate charge, usually.  I am worried that the LM3150 may not be able to drive some of these larger FETs.  I consulted the data sheet for the LM3150 but am having trouble discerning its maximum gate drive capability. Will the LM3150 be able to drive something like this?

    Here is the FET recommended by Webench:  http://www.ti.com/product/csd17306q5a

    The 40V FET has a higher gate charge threshold than the 30V one recommended by Webench.

    Thanks,

    Geovid

  • 0 in reply to Geovid Kali
    TI__Expert 3950 points

    Hello Geovid,

    I have generated a webench design with 60V FETs (see attached).

    1832.WebenchReportsServlet.pdf

    Could you please share your webench design?

    For what concerns the driver capability please take a look at page 4 of the datasheet.

    You will find  VCC current limit with a note saying "VCC provides self bias for the internal gate drive and control circuits [...]" of  65mA.

    The input current operating value is 5mA therefore there will be 60mA left. You can roughly calculate the maximum allowed switching frequency fsw = 60mA/(gate charge).

    This is something that webench does automatically and I think you can the 40V mosfet you mentioned.

    In any case we would like to take a look at your webench design since it is supposed to generate higher voltage mosfet.

    Regards,

    Giuseppe

  • 0 in reply to Giuseppe Pinto
    TI__Intellectual 2930 points

    Hi Geovid,

    Akshay mentioned you were looking for TI FETs in particular for these designs. The reason they are not showing up for your design is that WEBENCH wants more of a buffer between 36V-40V so it wont pick the 40V FETs, and the 60V FETs have not been added to our database yet (except for 1). I will request these get added.

    Best regards,
    Tommy Jewell 

  • 0 in reply to Tommy Jewell - WEBENCH Design Center
    TI__Intellectual 1245 points

    Hi,

    I was able to get webench to generate the higher voltage FETs when I lower my current requirement however, when I up the current to 12A I get no results.  I think this is because the AOS FETs are maxed out at 10A.  I am not sure what you want me to share since my design does not compile.  I am sure this issue will be resolved when the new 60V FETs are added as some of those are rated for extremely high currnt.

    Thanks for all the help,

    Geovid Kali