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UCC28070: Unbalanced current values supplied to A and B channels

Kaji@PAN
Mastermind 7330 points
Part Number: UCC28070

Hi,

I would like to ask a question about the UCC28070 device.
I am creating a board and checking the operation of the board.
The measurement waveform is attached.
It operates normally with a load of 4A, but if the load current value is lowered to 1A, the current value of the B side channel decreases.
When the output current decreases, does the current value supplied to the A and B channels become uneven?
Is this behavior normal?

Best regards,

  • 0
    TI__Mastermind 34465 points

    Hello Kaji,
    The phase currents in your scope shot for 1A load are:

    Do these current look unbalanced ?

    The scale is set at 5A/div. 
    You could change to 1A/div and measure the peak to peak values for A and then for B

    Regards

    John

  • 0 in reply to John Griffin1
    Mastermind 7330 points

    Thank you for your reply.
    The image you extracted is at 4A load.
    The image of 1A load is as follows.
    There is almost no inductor current flowing and the GDB pulse width is narrow.
    Does this situation occur as normal operation when the load is reduced?

    Best regards,

  • 0 in reply to Kaji@PAN
    TI__Mastermind 34465 points

    Hello Kaji,

    This is not normal and it shows that the current is not being shared between CH A and CH B.
    What is the maximum load current the pfc designed for ?

    The CSA,CSB signals are the inputs to the current amplifiers and you should compare these..
    CSA and CSB should be the same switching pattern and magnitude for the operating range of load current
    Check that the correct load resistor is used on the current transformers.
    Use the Excel calculator .
    If the load resistor is too small the measured signal will be small and difficult to measure accurately.
    This might cause an unbalance in the A and B channels.

    Regards

    John