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UCC27511: Problem with gate driver reference in PWM

Maria Aguilar6
Prodigy 30 points
Part Number: UCC27511

Hi,

I am using the model for LTSPice of the UCC27511 gate driver and I have some problems with them, probably because of the ground reference. I am simulating the ANPC topology as you can see in the attached picture with isolated gate drivers where the ground reference is in the middle point. Vdd is 7.2 V with respect the ground of each gate driver that is connected to the respective source of the transistors. However, the PWM pattern is created as shown in the las picture, and they are signals that go from 0V to 5V. If these signals are connected to the input of the respective driver the model does not work. Is there any problem with the PWM reference?

Thank you in advance.

Best regards,

Maria.

  • 0
    TI__Genius 12990 points
    Hi Maria,

    Welcome to e2e! thanks for asking about UCC27511, Im an apps engineer supporting this device.
    Whats your application? You mention an isolated gate driver. UCC27511 is not isolated, do you require an isolated gate driver?

    Is the GND pin voltage on UCC27511 0V or below 0V? If the GND is not 0V, and the PWM is going from 0V to 5V then the IN pin may not reach the input high threshold. In this case we will need a level shifter to properly reference the input PWM to the gate driver GND.

    Using a PNP transistor and a couple of resistors the input signal can be level shifted to the ground of the gate driver and by grounding the base the 5V PWM can turn on the transistor from the emitter while the collector sits on driver ground.

    Thanks,
  • 0 in reply to Jeffrey Mueller
    Prodigy 30 points
    Hi Jeff,

    That is exactly what happens. As you can see in the pictures, the gate driver are isolated so every ground is connected to their respective source (of each inverter that is gating). So the three bottom transistors have their sources connected to 350 V approximately while my PWM is going from 0 to 5V. Could you show me how I could solve this with a level shifter?

    I really appreciate your help.

    Thank you very much for all.

    Best regards,

    Maria.
  • 0 in reply to Maria Aguilar6
    TI__Genius 12990 points
    Hi Maria,

    Thanks for your update, sounds like quite an interesting simulation. I wanted to show you a couple of app notes that will help you out.

    First check out figure 2 in this app note on how the level shifter should be implemented. www.ti.com/lit/an/slua169/slua169.pdf
    Next check out how to drive the highside with a lowside driver in this app note. www.ti.com/lit/an/slua669a/slua669a.pdf

    Please let me know if you have any more questions!
    Thanks,