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TI UCC27714EVM-551

Emil Rosenzweig
Prodigy 30 points
Other Parts Discussed in Thread: UCC27714EVM-551, UCC28950

Can not get more than 40A output current from UCC27714EVM-551 (rated Vout 12VDC, Iout 50ADC).
With load gradually increasing output voltage drops down 30 mV, output current does not increase above 40A. Further load increase activates hick up mode.

  • 0
    TI__Genius 9130 points
    Emil

    Can you confirm the input voltage that you are using? This should be in the range 370-410 V dc.

    I will ask the engineer who designed the EVM to take a look at this post.


    Thanks,
    Bernard
  • 0 in reply to Bernard Keogh
    Prodigy 30 points
    Hello Bernard,
    Input voltage is 400VDC. The source is PFC rated for 1500W. Voltage is stable without 120 Hz AC component.
    Best regards,
    Emil
  • 0 in reply to Bernard Keogh
    TI__Intellectual 2061 points
    Hello Bernard,

    1. Would you please help confirm the input is still 400V when the PSFB enters hiccup mode?
    2. Would you please help measure the voltage at CS with minimized measurement loop? this pin has a internal 30ns filter to filte the noise. If possible, would you please send us a CS-GND waveform when hiccup mode happens, we would be able to provide you whether we need a filter and what is the filtering capacitance would be?

    Wei
  • 0 in reply to Wei Zhang
    Prodigy 30 points
    Gentlemen,

    How can I send you waveforms? Input voltage is still above 370V when hick up cycle starts. Output current is less than 40A. To get 40A I needed to reduce CS resistor value.


    Best regards,
    Emil
  • 0 in reply to Emil Rosenzweig
    TI__Mastermind 25570 points

    Hello Emil

    The EVMs are tested at full load (resistive) before shipping -

    I tried my own EVM here in the lab and with Rcs = 220 Ohms the current limit came in at 16A and the peak voltage at the CS pin of the UCC28950 was 2V - as expected.

    With Rcs = 110 Ohms the current limit went to 32A.

    With Rcs = 48 Ohms the current limit should be above 70A - but I don't have equipment at hand to allow me to load the EVM at 70A - which is why I've been using it with a higher value CS resistor.

    I'd double check a couple of simple things - has the CS resistor been damaged - is it still 48 Ohms.

    Are you sure that your load is not power limiting ?


     It depends of course on what you want to achieve from the EVM, but the Rcs is just a scaling factor and has no affect on the UCC28950 behaviour. One subtlety to be careful of though is that if you use a large value of Rcs the current limit point will come down. The output inductor ripple current will increase in proportion as you reduce the current limit point. For example, let's say you have 10A of ripple, that's 20% at Iout = 50A but 40% at Iout = 25A.

    Anyhow. please let me know how you get on.

    Regards

    Colin

     

  • 0 in reply to Emil Rosenzweig
    TI__Mastermind 40580 points
    Hello Emil,

    To include a file (such as waveforms, pdf, jpg, xls, etc.) with your posting, please click on the "Use rich formatting" roll-over button at the bottom-right of the text entry box. This will enable a formatting header to appear which contains a paperclip icon. Clicking on the paperclip will allow you to embed a file at the point where the text cursor is located.

    Regards,
    Ulrich