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UCC25600: burst mode

kwnag woon Lee
Prodigy 170 points
Part Number: UCC25600
Other Parts Discussed in Thread: UCC256301, UCC256402

Hello, we are currently developing 2kW AC/DC Rectifier. The output voltage is 43 ~ 56V and I am using LLC Converter to configure UCC25600.

The frequency range of ucc25600 is 40 ~ 350kHz, can the above output voltage range be possible?

The main output voltage is 54V and I set it to enter burst mode around 1A. However, as the voltage drops to 43V, the current entering burst mode increases, resulting in a waveform with output ripple entering burst mode.

Is it possible for the burst mode to go below 3A within the ucc25600's frequency range? Or should  I change to an IC like ucc256301 with a wider frequency range?

Please review.

Thank you.

  • 0
    TI__Guru 66065 points

    Hello,

    Generally you can design an LLC with a fixed output voltage with a variation of the input variation of 2 to 1. 

    If you input voltage is fixed the UCC25600 should be able to handle the 43 to 56 V output.

    Is the input voltage fixed when the output is dropping?

    Does the design work up to full power?

    Have you checked your design with the excel design tools to see if you can accomplish this with your Lm, Lr and Ln?

    There is a new family of LLC controllers.  The UCC256402/3/4 devices with a very adjustable burst mode and you can even disable it if you like.

    The data sheet can be found at the following link.  

    Regards,

  • 0 in reply to Mike O'
    TI__Guru 66065 points

    Hello,

    If you decide to move forwarded with the new UCC25640x devices their is also and excel design tool that you can use to aid in the design process.  The following link will get you to the tool below.

    Regards,

    Mike

  • 0 in reply to Mike O'
    Prodigy 170 points

    Hello, Mike O'

    Thank you for your attention.

    The input voltage is fixed at 390V over the entire output range.

    Cr is larger than the result of the excel design tool. 3 times bigger.

    At full power, it's working fine now. Weak vibrations in some sections are currently improving.

    I am worried because the lower the output voltage is, the more burst mode section becomes. Is it okay to operate for a long time in burst mode?

    The ucc2560x series that you suggested are under review and have a capacity of 2kW but I can't use a drive transformer because of the HS pin.

    Best regards.

    Kwang Woon Lee