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TPS2491: oscillation with low total charge FET

Lutz Naumann
Expert 6450 points
Part Number: TPS2491

Dear team,

we were experiencing oscillations on the Gate pin with a low total charge MOSFET. Putting a 1nF cap across Gate/Source already solved the problem at room temp. We are planning a 10nF cap to be on the safe side over temp and process variation. The 10nF was tested at room temp also. 

I would like to know, if we had any data that confirm what capacitance is needed to cover all corner cases? What is your experience and recommendation?

many thanks

Lutz 

  • 0
    TI__Expert 5940 points
    Lutz, duplicate to you email inquiry:

    The oscillation is possibly caused by the particular FET you are using may have a high transconductance (delta Iout/delta Vgs) combined with low Ciss. Make sure you use a gate resistor (10ohm to 30ohm recommended) along with added Cgs and it should stabilize. The exact values needed are FET dependent. If you found 1nF worked, a 10:1 safety margin should do the job. I would find the lower end, maybe less than 1nF to solve for your own knowledge purposes. If you don’t already have a gate resistor, add it. In some cases we see this solves by itself but I would still add some Cgs.

    Brian