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UCC39002: How many PSU can I implement parallel in a system?

Muhsiu Wei36
Intellectual 340 points
Part Number: UCC39002
Other Parts Discussed in Thread: UCC29002, UC3902

Hi Team,

Do you have any experiments or experience of parallel PSU using UCC39002?

What's the maximum PSU unit can we parallel in a system? if we would like to parallel more than 10 PSU units. Do you have any suggestion on this?

Meanwhile, I noticed there was another current sharing controller called UCC3902 which biggest difference between UCC39002 is differential current sharing signal. 

It seems to me, the differential current sharing bus(UCC3902) has better noise immunity than the single-end current(UCC39002) sharing bus. 

Is UCC3902 more suitable for our requirements? 

Thank you.

Muhsiu.

Noise immunity
  • 0
    TI__Mastermind 34465 points
    Hello Muhsiu,
    The upper limit to the number of modules is set by the output current capability of the of the current sense amp.
    This value is given in equation 1 of the data sheet.
    There have been reference designs built with up to 16 channels that use the UCC29002 load share controller and in practice you will probabbly find it difficult to use more than this number because of layout issues and accuracy associated with sensing such a large number of power modules.

    The UCC39002 is actually a better current sharing controller than the UC3902 because it has lower offset voltages and generally better defined parameters for its current amplifier. The UCC39002 has a differential current sense input so it can be used on the high side or low side.
    The UC3902 has a single ended input so it need to be placed on the return side of the load.
    Regards
    John
  • 0 in reply to John Griffin1
    Intellectual 340 points
    Hi John,

    Thanks for your reply. I have found PMP1099 reference design that using UCC29002 built up 8 channels.

    According to equation 1 of UCC39002 datasheet, assume VLs,FULL_SCALE is 7V. The number of modules will be (100K x 1mA)/7 = 14. Am I right?

    BTW, what's the maximum routing distance of LS signal?

    Muhsiu.
  • 0 in reply to Muhsiu Wei36
    TI__Mastermind 34465 points
    Hello Muhsiu,
    Yes. In your example 14 is the max number of load sharing modules.
    The routing distance is not specified for the LS pcb trace.
    As in all power supplies noise pickup should be avoided by routing the trace away from any external noise source.
    The outputs of the load sharing modules are DC signals so noise pickup is usually not a problem.
    Regards
    John