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TIDA-01606: UCC5320S schematic question

Howard Zou
Genius 12365 points
Part Number: TIDA-01606
Other Parts Discussed in Thread: UCC5320

Hi,

I have several questions for the schematic below:

1. why need 10ohm(R33) for the primary side 3V3, but not needed at the secondary side 12V and -5V? And why R33 is chosen to be 10ohm?

2. R10 and R50 are both 0ohm, I guess only one will be soldered in the final board, right?

If we solder R50, then there will be no negative power  supply at VEE2. Then do we still need C42, C43?

3. Why R36 and R39 are 3.3ohm? Is it chosen by calculation or by trying different value on the real board?

4. In this board we are driving IGBT with UCC5320. Are there anything different need to pay attention if we are driving SICFET? From both schematic and PCB layout point of view.

  • 0
    TI__Expert 3355 points

    Hi Howard,

    I work on the applications team in the high power drivers group and can help you with your question.

    1. The R33 10 Ohm resistor provides filtering for the 3.3V rail. This helps limit inrush current at start-up, and helps prevent switching noise from entering the 3.3V rail through the common mode path during operation. 10 Ohms was probably chosen to limit inrush current due to the large amount of capacitance being charged by the 3.3V rail.
    2. According to the PDF schematic, R50 is marked as DNP. Correct, if you do include R50, there will be no negative power supply, and C42, C43 are not needed. You would also not need the Zener regulator circuit.
    3. These values were chosen for a variety of reasons. In general, gate resistors are chosen to limit ringing due to parasitic inductance in the drive loop, which helps mitigate EMI. Please see UCC5320 datasheet, section 11.2.2.2: Gate-Driver Output Resistor, to learn more about the gate driver output resistor calculations. Also see this tech note to learn more about fine tuning the value for your circuit. http://www.tij.co.jp/jp/lit/an/slla385/slla385.pdf
    4. Generally, I’ve seen SiCFETs require +15V/-5V, so that’s one thing to consider. SiCFETs generally switch faster than IGBTs and more care will need to be taken in the layout process to ensure inputs stay well filtered, and outputs have lowest inductance loop as possible. Please read through this application note on the importance of layout in isolated driver circuits. http://www.ti.com/lit/an/slua897/slua897.pdf

    If this answered your question, could you please press the green button? If not, feel free to keep asking questions.

    Thanks and best regards,

    John