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Original question:

TIDA-00917: Calculate the CM inductance value

TIDA-00917: IGBT Gate driver - CM choke sizing and current rating

Ye Zhao
Prodigy 180 points
Part Number: TIDA-00917
Other Parts Discussed in Thread: UCC21732

hi, TI support

The reference design TIDA-00917 seems to be very helpful.

May I ask the following questions:

1) how to size the CM choke used for IGBT gate drivers to drive multiple IGBTs in parallel?

2) How to choose the current rating of the CM choke?

3) R34 and R35 are for Desat for top and bottom Driver IC, correct? Any rule of thumb to pick the resistance?

Any good reference would be very helpful.

Thanks

YZ

www.ti.com/.../TIDA-00917

  • 0
    TI__Expert 3580 points

    Dear YZ,

    thank you for your interest in TIDA-00917.

    Regarding your question on how to size the CM choke, could you check the following E2E post?

    We've had a similar question on the calculation of the common mode choke, which was addressed here.https://e2e.ti.com/support/tools/simulation-hardware-system-design-tools-group/sim-hw-system-design/f/simulation-hardware-system-design-tools-forum/927251/tida-00917-calculate-the-cm-inductance-value

    If this E2E post does not answer your question, please let me know. 

    Regarding your question on how to size R34 and R35, we will check with the designer and get back to you.

    Regards,
    Martin Staebler

  • 0 in reply to Martin Staebler
    Prodigy 180 points

    Thanks. I found this thread as well. It mentioned about the CM inductance.

    Two other questions are not answered directly.

    2) How to choose the current rating of the CM choke?

    3) R34 and R35 are for Desat for top and bottom Driver IC, correct? Any rule of thumb to pick the resistance?

    Thanks

    YZ

  • 0 in reply to Ye Zhao
    TI__Expert 3580 points

    Dear YZ,

    thank you for your quick feedback. I'll check both questions (size of R34 and R35 and CM choke rating current) with the designer and get back to you latest by Friday 11/17 on the status of the analysis.

    By they way, in the mean time we have an isolated IGBT gate driver UCC21732 with a +/-10A sink/source current. https://www.ti.com/product/UCC21732, in case your application does not required more than +/-10A.

    Regards,
    Martin Staebler

  • 0 in reply to Martin Staebler
    TI__Expert 3580 points

    Dear YZ,

    we've consulted the designer. 

    Question: How to choose the current rating of the CM choke?

    Answer: The a    verage current value is used rather than the peak current value. Peak current ratings are ~8A and inductors rated this value are going to be large in size and cost. For a given PWM cycle most of this peak current is close to rise and fall edges, once gate capacitor is charged current is almost null.

    For example: The TIDA-00917 was designed for up to 10uC gate charge. Assuming a 8kHz PWM, the average CM chock current would be ~ +/-160mA (average turn on/turn off current). The 250mA rating of the DC choke would add margin here. 
    In any case we recommend that you validate the DC current rating of the CM choke and tune as required for your specific design. 

    Question: R34 and R35 are for Desat for top and bottom Driver IC, correct? Any rule of thumb to pick the resistance? 

    Answer: Yes, the resistor R34 and R35 offers a low impedance / short circuit path across the winding of the CM choke for the short circuit transients to be detected by DESAT circuit. We don't have a formula to calculate these resistors. A 10mOhm resistor was used and gave reasonable results as shown in the TIDA-00917 design guide section 4.7 Short-Circuit Test. We recommend you validate and tune with your specific design.

    Regards,
    Martin Staebler

     

  • 0 in reply to Martin Staebler
    Prodigy 180 points

    Thank you very much.