UCC27282: Role of input capacitors in the UCC operation

Part Number: UCC27282

Hello,

How to select the HI and LI capacitance values. i observed the response with10nf capacitance and without capacitance. I observed that without any capacitance the input and output pins are oscillating during high mode (LI and LO). with 10nf capacitor i am getting stable signal. Please give me the role of this capacitor in the UCC operation. 

and i also observed that there is voltage fall down in short period at input and output pins (LI and LO). what causes this voltage fall down. 

  • Hey,

    Thank you for reaching out to TI regarding your questions about the UCC27282.

    The capacitance that we recommend in HI/LI is a part of an RC filter because we also recommend a resistor in series with HI/LI to form that RC filter. This RC filter will help with any noise from your controller signal so that the gate driver receives a clean signal. Typical values we see for this RC filter are 0-100ohms and 10-100pF.

    For this waveform you are seeing the voltage dip on, is that with or without the 10nF capacitor?

    Let me know if you have any questions.

    Thank you,

    William Moore

  • Thank you for your reply. i know that the capacitor (RC filter) to filter the noise. i want to know, what is its role in terms UCC operation. otherwise give, what is maximum current that the input pin can draw when it is enable. how this capacitor helping to reduce the spike. the above fig is with 10nf. i have observed results with and without capacitor, so, without capacitor the driver output will not get properly. (it is fluctuating). 

  • Hey,

    For the gate driver, if there is excessive noise on the inputs, the driver can propagate unexpected outputs by seeing the ringing as another rising or falling edge. Providing a clean square wave to the driver helps to ensure expected operation. The 10nF capacitor is larger than typical.

    Can you try 100pF and take waveform captures to see that?

    What input resistor are you using for the RC filter?

    Let me know your responses to these questions and if you have any further questions.

    Thank you,

    William Moore

  • Hey,

    Have you been able to resolve this? If so, what was your solution? If not, can you please provide an update on the status and what you have tried to do to resolve it.

    Thank you,

    William Moore

  • Hey,

    I am going to close this thread. If this has not been resolved, please respond and reopen this thread and update with the status of it and any questions that you have. If it has been resolved, please let me know what the resolution that you found was.

    Thank you,

    William Moore