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

Srijeeth J

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?

3 months ago

0 Sasikala Thangam 3 months ago

TI__Expert 5530 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 Srijeeth J 3 months ago 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 Sasikala Thangam 3 months ago in reply to Srijeeth J

TI__Expert 5530 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

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