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UCC27211A-Q1: TIDUCB6

Part Number: UCC27211A-Q1

Hi,

Thank you for the wonderful analysis and documentation of 48-VDC Battery Powered Inverter Power Stage Reference Design for 5-kW Forklift AC Traction Motor.

I have some queries on this design guide: 

1. How R2 and R20 has been selected in figure 6.

2. Can I remove 0.5 from equation 8 & 9 if i am not using soft switching?

3. Apart from conduction & switching losses, there are other losses mentioned in MOSFET power losses and how they affect power-supply efficiency (ti.com).

    But they do not comply with the existing design TIDUCB6, if i could help on the equation derived for losses other than conduction and switching losses with respect to this design, it would be helpful.

Thank you.

  • Hi Samant,

    Thanks for feedback for our documentation.

    Our expert is out of office right now and he will get back to you on Tuesday. Monday is a US holiday.

    Best Regards,
    Ethan Galloway

  • Hi Samant,

    Thank you for reaching out, and I'm glad you found the power stage reference design article useful!

    In response to your questions:

    1. R2 and R20 are split external gate drive resistors meant to optimize switching frequency and EMI performance. TI offers a TechNote that explains how to start with a 0-Ohm resistor and calculate a new external gate driver value using ring frequency, source inductance, and input conductance. The TechNote for choosing the external gate driver value can be found here: Link.

    2. Yes, the 0.5 scaling factor accounts for the device soft-switching half the time. Since you are not soft-switching, you should be able to remove the 0.5 scaling factor from equations 8 and 9.

    3. For clarification, are you asking which losses need to be considered outside of conduction and switching losses for the MOSFET and how to calculate them? Can we assume that the system is similar to the 48VDC Inverter Power Stage Reference Design?

    Best,

    Alex Weaver

  • Hi Alex,

    Thank you for reverting back. Yes, system is similar to 48VDC Inverter Power Stage Reference Design.

    Thank you

  • Hi Samant, thank you for the clarification!

    All images, figures, and equations are taken from the MOSFET losses article. The image above is a basic switching circuit (shown in Figure 4) where Q1 is the high side MOSFET and Q2 is the low-side rectifier MOSFET. In Q1, we will be concerned with conduction losses, switching losses, and gate losses (shown in Figure 8). The equation for gate loss in the MOSFET is shown in Equation 5.

    In addition to the gate losses on the MOSFET Q1, there will also be gate drive losses due to the internal resistance of the gate driver. The formula to calculate the total gate drive losses is shown in Equation 6. This same equation can be used to calculate the gate losses in Q2.

    Figure 11 shows all the losses we will need to calculate for Q2. The only power losses specific to Q2 outside of conduction losses and gate losses will be body diode losses. Equations 9a through 9e show how to find the body-diode current and Equation 10 will allow you to use the calculated current to find the body-diode power loss.

    I hope this answers your question!

    Best,

    Alex Weaver