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LMG3410R070: LMG in Series

Sam Ref
Expert 1610 points
Part Number: LMG3410R070

Hello

We have a power inverter application that requires over 750VDC. Is there any constraint imposed by LMG3410 that would stop us using 2 LMG3410 in series to raise their voltage blocking capability? In that case a 3-phase inverter would use 12 LMGs (4 per leg) rather than 6 LMGs. Please see the attached pictures minus the FWDs. Please note that in our application we do NOT intend to use 3-level inverter. It is a normal two-level inverter. The picture attached is only there to  show the power switches configuration where the power switches are connected in series.

Regards

Sam

  • 0
    TI__Expert 3225 points
    Hello Sam,

    Thank you for the question. To give you a short answer, the simple series connection cannot guarantee the good voltage balance between two FETs but some active voltage balance is required.

    There will be some variation on device prasitics so that the Cds and Cgd will all be different. Plus for each of the FET in the circuit, its associated parasitic inductance will be different. This can result in one FET turning off faster than the other. Therefore, the voltage division between the two FETs will finally run apart. Some literatures show some gate drive technique to balance the voltage, but it would need extra components in the circuit.

    Hope this helps.

    Thanks and regards,
    Lixing
  • 0 in reply to Lixing Fu
    Expert 1610 points

    Hi Lixing

    Thanks for your answer.

    Do you have a reference to that gate drive technique to balance the voltage?

    Does TI have any reference design for that extra components in the circuit?

    Would you know whether the three-level configuration provide that voltage balance?

    Regards

    Sam

  • 0 in reply to Sam Ref
    TI__Expert 3225 points

    Hi Sam,

    Thanks for your interest. Yes, there is a paper from Virginia Tech talking about this. "Active Gate-Driver With dv/dt Controller for Dynamic Voltage Balancing in Series-Connected SiC MOSFETs". Please go to IEEE website to find it. Unfortunately there is no reference design from us to demonstrate this application. 

    For sure a three-level design will automatically balance this since the capacitor soft-charge or neutral clamp mechanism will help with the voltage balance. People have done this already with our GaN. Please look into the link below for more information.

    training.ti.com/ti-siemens-taking-gan-grid

  • 0 in reply to Lixing Fu
    Expert 1610 points
    Thank you Lixing
  • 0 in reply to Sam Ref
    Expert 1610 points
    Thank you