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TPS40195EVM-001 20V to 3.3V MOSFETs warning about gate charge

akircan
Intellectual 350 points
Other Parts Discussed in Thread: TPS40195EVM-001, SWITCHERPRO, TPS40195

When I use the "TPS40195EVM-001 20V to 3.3V" as design and change the MOSFETs(Q1 and Q2)  to other MOSFETs and then change it back to the original values I get a warning:

IRF7821 for Q1:
Maximum qty recommended to keep from exceeding gate charge spec = 3

IRF7832 for Q2:
This MosFET's Gate Charge (34nC)  exceeds the recommended value for this position. The recommended value for this position is 30nC.

I started a new design and I also get this warnings, if I use these MOSFETs.

Why are these MOSFETs used in the EVM ? Is the warning ignored for the EVM? Or is the effect on the conduction losses negligible ?

Andreas

  • 0
    TI__Expert 3875 points

    Hi Akircan,

    I recently saw your post. This EVM was developed before this device was integrated into SwitcherPro. So, this design did not originate in SwitcherPro.

    As far as I can tell, the data sheet does not specify a maximum allowed gate charge for the TPS40195. So, SwitcherPro is using a know good conservative safe default value.

    In this particular case, SwitcherPro is more conservative than the EVM. But, these FETs work fine in this EVM. So, they should be safe to use.

    Regards,
    Michael