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Thread: 6EDL04N06PT - High Side MOSFET Switch Off Issue / Phase Voltage

  1. #1
    New Member New Member SafetyLok is on a distinguished road
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    6EDL04N06PT - High Side MOSFET Switch Off Issue / Phase Voltage

    Hi,

    I have a 6EDL04N06PT connected to 6x STF10N60DM2 MOSFETS, the design is used in a BLDC Inverter. I have the PWM operating in an open loop mode and I'm using this to qualify the MOSFET switching times.
    I have a resistor load from the phase to GND, which is 820R for this test. The VDC bus is 30V (although it will be used at 100V) and my VCC is 16V.
    I have removed all gate resistors so there is some slight ringing.
    I have 100nF of boot strap capacitor.


    The diagram below shows my setup, with the scope channel colours circled.
    Click image for larger version

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    The scope capture below shows the following:
    D0 and D1 are the PWM 1H / PWM 1L Inputs
    Yellow is the gate voltage at the Lower FET
    Purple is the gate voltage at the Upper FET
    Blue is the phase voltage.
    White is the Upper FET Vgs (math)

    Click image for larger version

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    I can clearly see that the phase voltage remains at VDC and decays through the load resistor when the High side MOSFET is switched off. There is a significant amount of energy in this system, and during the low side switch-on (yellow) the remaining energy in the phase drops to zero creating a significant transient.

    I feel that the upper MOSFET is actually switched off (based on the Vgs < Vth of 4.0V) and there is no capacitance or inductance anywhere in my circuit that would cause this type of issue.


    My questions are:

    1. Is the gate driver actually turning the upper FET off?

    2. Is there something in the bootstrap circuit that would store sufficient energy to cause this problem?

    Thanks
    SafetyLok

  2. #2
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    Infineon Employee
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    IrisLi is on a distinguished road
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    Please firstly try to measure the VBS voltage (between VB1 pin and VS1 pin) with a differential probe to see if this voltage is lower than UVLO level, if yes, then it trigger UVLO protection, the high side will be off.
    The views expressed here are my personal opinions, have not been reviewed or authorized by Infineon and do not necessarily represent the views of Infineon.

  3. #3
    New Member New Member SafetyLok is on a distinguished road
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    Thanks,

    I have checked the VB-VS and its well above the UVLO voltage at all times.

    Can you advise me if the 6EDL04N06PT is able to be used with 3 current shunt resistors? (i.e. the COM pin and VSS pin joined).

    Thanks.

  4. #4

    Infineon Employee
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    Srivatsa is on a distinguished road
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    Yes, the COM pin and VSS pin can be joined together.

    The 6EDL04N06PT can be used with 3 current shunt resistors.

    In this case the ITRIP pin of 6EDL04N06PT can be used to detect current from one current shunt resistor only.
    The views expressed here are my personal opinions, have not been reviewed or authorized by Infineon and do not necessarily represent the views of Infineon.

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