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TIDA-01606: Connect MCU GND with Power GND

Nam Trinh
Prodigy 20 points
Part Number: TIDA-01606

Tool/software:

Hi,

I am design and testing a three-phase inverter design based on TIDA-01606.

I have a question regarding the Power Ground Plane and MCU Ground plan:

In the TIDA-01606 design the MCU GND connect to Power GND by a ceramic cap 2200pF, what is the purpose of this connection? what if we isolate MCU GND and Power GND completely, no connection?

Why the designer do not use negative point of DC link voltage (DC-) as Power GND?

Can we select negative point of DC link voltage (DC-) as Power GND and connect with MCU GND directly?

Thank you.

  • +1
    TI__Expert 7855 points

    Nam,

    we are getting close to updating the 1606 design.  Please see attached for the latest E7 schematic.

    There are basically three common options when it comes to MCU ground reference: 

    1) DC Link midpoint (VDC_MID) - the voltage of this is close to the Neutral voltage of the 3P grid.  This midpoint voltage can vary if not properly regulated so the offset from the Neutral voltage can be high.  Thus, consider using an isolated aux power supply for the low voltage side.

    2) DC Link Negative (VDC-) - this is fine.  we see some people use this option but you will have to consider isolation

    3) Earth Ground

    For 1 & 2, you will have to consider using an isolated power auxiliary supply (e.g. 24V) as your 3P AC Source (e.g. chroma) might not be isolated from your bench aux supply.

    The point is to float your MCU onto either  VDMID or VDC-.  Without proper isolation, you might experience overvoltage stress on your low voltage rails.

    For option 3, since the power stage is isolated from earth already you don't need to have an isolated aux supply.  

    5153.TIDA-01606E7(001)_Sch.PDF

    -Kelvin

     

  • 0 in reply to Kelvin Le THS
    Prodigy 20 points

    Hi Kelvin,

    Thank you for your feedback.

    So in the latest design of TIDA-1606, TI will provide options for user to configure either VMID, VDC- or floating MCU GND.

    It will be direct wire connection, not through a Y cap anymore.

    Thank you.

  • +1 in reply to Nam Trinh
    TI__Expert 7855 points

    Nam,

    That's correct.  Technically, if you look at the emi filter stage, the Y caps provide isolation from the AC grid to earth ground.

    The point is, isolation needs to be respected.

    as i mentioned, the VMID, VDC- direct connection will require you have use isolated aux power supply.

    For direct connection, i would recommend using a ferrite in place of R10 resistor for emi reasons.

    -Kelvin