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TPS92410: TPS92410 Error in the datasheet - Over voltage protection - Rground calculation.

Miguel Camus
Prodigy 120 points
Part Number: TPS92410

Hi There!

I'm using the TPS92410 for a design working at 120VAC and I've found a problem in the over voltage protection section. It recommends to use Rground as 121K and then calculate the Rdrain using the equation. 121E3 * ((120-1.5)/1.5) = 9560000 (9M56) ] but in the suggested Figure 12. "Application schematic" the value is 2M!!

Is it wrong?

Kind regards,

Miguel

  • 0
    TI__Mastermind 28655 points

    Hello,

    The equation is correct, Vovp is not 120 VAC unless you want the OVP to trip when the average drain voltage is 120V.  The idea for OVP is to figure out what average voltage is on the drain of the MOSFET during high line operation.  One way is to measure it at the OVP pin with a chosen value, or increase the AC input until it trips.  Also make sure the DOV capacitor is large enough to prevent OVP from tripping during turn on.

    If the average drain voltage, worst case, was 30V average the equation would give you 2.3 Mohm.  30V average on the drain should be much higher than the average at 120V.

    A three channel design with 84V/42V/21V LED strings will have a total series voltage of 147V, the peak of the rectified AC is 169V at 120VAC.  The difference is 22V at the peak of the rectified AC.  The average voltage, due to the sinewave and TPS92411s switching will be quite a bit lower than this.

    Regards,

  • 0 in reply to Irwin Nederbragt
    Prodigy 120 points

    Thanks for your answer Irwin, I get it now!

    Kind regards,

    Miguel