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TIDA-00917: Calculate the CM inductance value

Intellectual 850 points

Replies: 6

Views: 99

Part Number: TIDA-00917

Hi Team,

 I have two questions:

 1. Can I have to know how to calculate the CM inductance value in this schematic? Based on what?

 2. I noted Infineon has been released a IGBT/MOSFET driver which is constant current type, the link as following. As documents mentioned, which have more benefits compare with voltage driver type. Could you have any comments for current type IGBT/SiC Mosfet driver? Advantage and disadvantage? Thanks. 

Notes:

https://www.infineon.com/cms/en/product/power/gate-driver-ics/1eds20i12sv/

https://www.infineon.com/dgdl/Infineon-Silicon-Carbide_(SiC)_MOSFETs_using_EiceDRIVER(TM)_Advanced_Gate_Drive_Options-ApplicationNotes-v01_01-EN.pdf?fileId=5546d4625b3ca4ec015b47c9ac35705b

https://www.infineon.com/dgdl/Infineon-Gate_Drivers_Boost_IGBT_Performance_Bodos_Power_Systems-ART-v01_00-EN.pdf?fileId=5546d46266f85d6301670826b055322b

https://www.infineon.com/dgdl/Infineon-PCIM_2015_Slew_rate_control_of_discrete_IGBT_and_CoolMOS_reaches_targets_far_beyond_the_gate_resistor_regime-Article-v01_00-EN.pdf?fileId=5546d46250cc1fdf0150d23a77d35e54

Thanks. 

BR,

Xiaobing (Eric) 

  • Dear Eric,

    Many thanks for your questions. I am in contact with the designer and will come back to you shortly.

    Best regards,

    Michael

  • In reply to Michael Seidl:

    Hi Michael,

     Thanks, Michael. 

    BR,

    Xiaobing (Eric)

  • In reply to Xiaobing (Eric):

    Hi Eric,

    Many thanks for your patience.

    For the first question – CM inductance is meant to equalize the gate voltage and hence equal collector current sharing. The impact is based on the module stray inductance, di/dt of the inverter, layout of the gate driver and power supply. Section 2.2.3 of the design guide explains the phenomenon but we don’t have any formula to calculate CM value. Roughly 5000 times of stray inductance could be a starting point to fine tune based on the system – and it depends on what level of current sharing is acceptable between IGBT’s.

    For the second question - Constant current drive can be beneficial under certain conditions. A constant current output driver would not need an external gate resistor which means the gate driver dissipates the power inside the driver which should be considered. A constant current output driver could be slightly more costly than a pure voltage driver due to different internal architecture. This specific IFX device has a lot of extra features, such as controlling the slew rate, and I cannot comment to what extend it will serve your needs for your application.  

    TI offers DRV835x three-phase motor driver with integrated smart drive technology which includes among several other features also a constant current drive capability. DRV835x is rated for up-to 100V. I am not sure if this would work for you. As said, constant current is not a bad thing and it is not unknown to TI. It is just a matter of having the right feature set at the right cost.

  • In reply to Michael Seidl:

    Hi Michael,

     Noted with thanks for your comments. 

     For 1st questions, personal I don't think the common (CM) inductance could equalize the gate voltage for parallel IGBTs, the common-mode choke works as inductor against a common-mode current for ITBTs. If purposes are equalized the gate voltage between different IGBT, a differential (DM) inductor should be populated between IGBTs or SiC-Mosfet, please see above diagram. How do you think or any-other method suggestion? Please correct me if anywhere is wrong. 

     Plus, thanks for your comments for CM inductance, I'm clear your purpose. 

    BR,

    Xiaobing (Eric)

  • In reply to Xiaobing (Eric):

    Hi Eric,

     

    I am glad to read that I could help clarifying the CM inductance’s purpose. I am not sure if we would mean the same when you call it working against a common-mode current for the IGBTs. I would have called it working against the circulation current in the IGBT’s emitter path. Either way, TI might not be the right company to answer such questions on the IGBT usage best. The purpose of the TIDA-00917 is to show the capability and performance of the TI gate driver product and that it can be enhanced to 15 Apk with external BJT buffer stage. In order to show that, real IGBTs were added in parallel and the designers used common design practices and optimization to assure good enough performance. For getting down to all the ‘tips and tricks’ of optimizing the IGBT performance to its maximum it would probably be best to contact the IGBT vendors themselves. I believe each vendor would have its own recommendations for using their products best, including the necessary simulation models and support. I am sorry for not being able of much further help on the IGBT sub-system itself.

     

    Best regards,

    Michael

  • In reply to Michael Seidl:

    Hi Michael,

     Thanks for your feedback,now we're stay on the same page.

     The parallel IGBT's ((SiC, not limit 2 pcs, 10pcs or more) emitter circulation current will be suppressed by CM choke. If the purpose is driver parallel IGBT's at same time, one way is try to used a differential choke. 

    BR,

    Xiaobing (Eric)

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