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Original question:

UCC28711: 400- to 690-V AC Input 50-W Flyback Isolated Power Supply Reference Design for Motor Drives

UCC28711: UCC28711:

seungpyo kang
Prodigy 100 points
Part Number: UCC28711
Other Parts Discussed in Thread: TIDA-010000, TIDA-00173, UCC28740

Tool/software:

Thank you very much for your help. Thanks to you, I am fully engaged in the development of SMPS as recommended by TI.

To use SiC MOSFETs (before i asked to here and i recommand upper document), the recommended documents suggest using push-pull circuits.

Reference document : 

1. TIDA-010000

2. TIDA-00173

Questions:

1. Do you select the gate drive circuit based on the MOSFET's Coss value? If so, I am curious if there are specific criteria or calculations for Coss.

2. I would also like to know the criteria for selecting R48, R19, D24, and R50. If there are any reference documents, please let me know.

3. Additionally, some documents show a resistor at the TP12 position, while others do not. I am curious about this as well.

<TIDA-00173>

<TIDA-010000>

  • 0
    TI__Mastermind 25755 points

    Answers to each question below:

    1. Do you select the gate drive circuit based on the MOSFET's Coss value? If so, I am curious if there are specific criteria or calculations for Coss.

    Gate drive bias power is determined by P=Q*V*F and gate drive current is estimated by Q=I*t and the gate charge, Q is found in the SiC data sheet, I is the gate driver peak source/sink current and t is the resulting rise (or fall) time. Q is also equal to C*V but I prefer to use Q instead of Coss because Coss is very non-linear and has a strong dependance on VDS. 

    2. I would also like to know the criteria for selecting R48, R19, D24, and R50. If there are any reference documents, please let me know.

    R19, R48 and D24 make up a circuit used to control/limit the turn on/off, source/sink gate drive current independently. D24 should be a low Vf Schottky diode, R48 and R19 are placeholders and the values are tuned on the bench to give the VGS desired speed and control/dampen any gate drive ringing. I prefer to place R48 in series with D24 but either method is acceptable and popular. R50 is imply a pull down resistor used to make sure VGS of the SiC is never floating. 4.87kΩ is ok but more common to use 10kΩ.

    3. Additionally, some documents show a resistor at the TP12 position, while others do not. I am curious about this as well.

    Be careful - if R18 is installed in the circuit you are showing, you would short the Vbe junction of each bipolar. I'm not sure what the intent is but maybe to bypass the external npn/pnp totem pole driver and drive the SiC directly from the UCC28740? R18 is not a typical component placement. the fundamental circuit should look something like below but you can also add R48, R19, D24 and R50 as discussed in (2) above.

    For more detailed knowledge about everything related to gate drive, please refer to Fundamentals of MOSFET and IGBT Gate Driver Circuits.

    Regards,

    Steve