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UCC21750-Q1: How to design the blanking series resistor in the DESAT circuit??

Srijeeth J
Prodigy 30 points
Part Number: UCC21750-Q1

Hello TI,

The DESAT function requires the 3 external components, R, C_BLK, D_HV. 

Could you please share knowledge on the design requirement for the series resistor (R - shown in the figure below) ? What is the recommended value? What are the factors affecting the selection of this resistor?

  • 0
    TI__Expert 6930 points

    Current limiting resistor R is used to limit the current pulled out of DESAT pin esp due to parasitic capacitance of the HV blocking diode. Its recommended to plan ~500ohms to 1 Kohms, Ensure that the voltage drop across the resistor is as needed to fulfill the DESAT threshold requirement of the power module.

    Gate driver threshold = voltage drop across Rlimit + HV blocking diode voltage+ voltage across the power module.

    Please refer the following FAQ about DESAT Threshold adjustment : [E2E FAQ] Adjusting DESAT Threshold. Hope it helps.

    Thanks

    Sasi

  • 0 in reply to Sasikala Thangam
    Prodigy 30 points

    Thanks you for the valuable information. I got some understanding of the use of the resistor, but could you please help me with some equations to design the optimum value of resistor. How should I think to arrive at a value for the resistor instead of using general thumb rule??

  • 0 in reply to Srijeeth J
    TI__Expert 6930 points

    Hi Srijeeth,

    Please plan at minimum > 500 Ohms and then any value higher will be to adjust the threshold needed for the power module in the system. Also please check the following calculator to adjust the capacitance for timing and resistor value for the threshold calculation.

    UCC217xx XL Calculator Tool