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Original question:

ISO5852S-Q1: Whether we can add a external voltage source to the Desat pin to speed up the charging of the blanking capacitor...

ISO5852S-Q1: ISO5852S-Q1

Adrian Ocampo
Prodigy 60 points
Part Number: ISO5852S-Q1

We completely removed the DESAT blanking capacitor, but the voltage on the DESAT pin is still ramping and takes about 7uSec to reach 7V.  We also removed the Schottky diode that's was in parallel with the Capacitor but it did not make a difference with the timing.  Finally, we verified the capacitance to be <5pF and still no difference.  Is this an inherent function of the device?  We are also thinking of using a pull-up resistor to speed up the timing. 

  • 0
    TI__Guru**** 189399 points

    Hi, Adrian,

    We have a pretty weak current source charging that node (500 uA). Looking at plots 15-18, I would assume you'd be faster than 7 us. With a 220 pF blanking cap, we see 4-5 us for it to charge to the threshold level. I think you have some excess capacitance/leakage somewhere on your board.

    Maybe it's the junction capacitance of your HV blocking diode slowing it down?

    If you speed it up with a resistor, of course the trade-off is you might experience false trips due to ringing on the collector.

  • 0 in reply to Don Dapkus
    Prodigy 60 points

    Thank you for the quick response.  I will look into the HV blocking diode.