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UCC28251: External synchronization and output parallel

user4657807
Prodigy 120 points
Part Number: UCC28251
Other Parts Discussed in Thread: UCC39002, , UCC29002, TPS2419

Hello,

thanks for handling this question.

question 1,

I saw on page 17 of the datasheet:

If the frequency source is from the gate outputs of another half bridge controller,interleaving can be achieved.

So, how do I achieve interleaving. Is it only necessary to connect the RT pins of the two controllers and set the RT resistance? Or is there a connection diagram for reference?


question 2, 

We want to design a 390 input 24V/1400W DC-DC converter. And use a planar magnetic core to meet the small size requirements. I chose four 350W converters in parallel to achieve. Each converter is designed by UCC28251, and the current sharing is realized by ucc39002. Is there a problem?
Thank you

Thank you！

  • 0
    TI__Mastermind 40580 points

    Hello User4657807,

    Thank you for your interest in the UCC28251 PWM controller.

    I will refer your questions to an expert for this part.  Please allow a day or two for a reply.

    Regards,
    Ulrich

  • 0 in reply to Ulrich Goerke
    TI__Mastermind 34465 points

    Hello User4657807,

    The data sheet is not clear on how to achieve interleaving and hopefully I can better explain the correct procedure for synchronising and interleaving.

    To synchronise two controllers you will need to set both controllers at the approximately same free running frequency with a resistor on RT
    Then you will require an external synchronising oscillator running at about 10% higher oscillator frequency.
    The external oscillator needs  A and B outputs where A and B are 180 degrees out of phase .
    A is applied to the RT input of one controller
    B is applied to RT input of the other controller.
    If you wish you can use the outputs of another half bridge controller to generate A and B signals.
    If you use this method then you will need the oscillator of the synchronising controller to run at twice the frequency of the other half bridge controllers.
    This is because the outputs A and B are running at half the oscillator frequency.

    In answer to your second question you will be able to achieve current sharing with the UCC29002 load share controller.

    Regards

    John 

  • 0 in reply to John Griffin1
    Prodigy 120 points

    Okay, thanks for replying to this question.

    Also, do I need to add oring mosfet in parallel to prevent reverse current? Is this necessary?

  • 0 in reply to user4657807
    TI__Mastermind 34465 points

    You will not need an ORing diode if all 4 of your power modules are always powered on and providing load current.
    If you wish to switch on and off any power module then you will need an ORing diode such as the TPS2419

  • 0 in reply to John Griffin1
    Prodigy 120 points

    Oye, all 4 of your power modules are always powered on.
    Does "providing load current" include no load and light load? Or it must be more than half a load.

    thanks