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ISO5452: Is there any concern with 9V DESAT threshold voltage?

Part Number: ISO5452

Customer was concerned about 9V of the DESAT threshold voltage of ISO5452, since they are afraid the short circuit current might go up a lot until the voltage reaches up to 9V. I believed it should be okay if using a small capacitor to achieve a short capacitor charging time. Could you please help address why we designed 9V for the DESAT threshold voltage and how to address their concern? Thank you. 

  • Aki, 

    Is the customer driving SiC FETs?

    DESAT system and 9V threshold was originally intended for IGBT protection  as this is where the current knee is on most devices (where they leave saturation region and enter linear), though the threshold of detection can be very easily adjusted through passives. 

    I would not choose a blanking capacitor lower than ~100pF as you are then relying more on the parasitic cap and cap of the DESAT pins to charge and your estimate of blanking time will not be close to the actual value. If they need shorter detection time i highly suggest they stick with a larger cap (perhaps around 220pF) and instead increase the charging current with external resistor (see my FAQ below)

    If they are driving IGBTs, there should not be any problem with using DESAT system there as it is extremely well suited for IGBTs. If they are driving SiC, that is another story, and the following FAQs will be very important, as you will want a short blanking time (~100ns nominally) and ~5V effective detection threshold. 

    We actually have a couple FAQs on e2e that should perfectly address the customers question on how to tune DESAT whether for IGBTs or SIC, there are also downloadable PDF which you are welcome to share with the customer. 

    * How to Increase charging current with DESAT 

    * How to adjust DESAT threshold

    Please let me know if you have anymore questions, otherwise could you press the green button to mark this as resolved?

    Best

    Dimitri

  • Hi Dimitri,

    Thank you for the detailed guidance. Customer used IKW75N65EH5 and they thought it was still required to reduce the DESAT threshold. 

  • Aki, 

    The optimal desat threshold varies by device, they may need to adjust it. Once they put a DESAT diode and series resistor it will be somewhere areound 7V depending on how many HV blocking diodes they have used (1 or 2)

    If they are not going to use the "increase charging current method", they can use UCC217x DESAT threshold calulator to help guide the design, but note that the other pages will not work as the design values are different. 

    Please let me know if you have anymore questions, otherwise could you press the green button to mark this as resolved?

    Best

    Dimitri