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Original question:

UCC39002: UCC39002

UCC39002: UCC39002

Waseem Akbar
Prodigy 60 points
Part Number: UCC39002
Other Parts Discussed in Thread: UCC29002

Hi, 

I'm utilizing the UCC39002 current share circuit to parallel two power modules and was wondering if there are any design examples mentioning how to use the device when there is a "trim" adjustment made to the output power modules like the example shown below. The trim simply means adjusting the output voltage of the power module by a certain percentage. This trim adjustment ties directly to the sense(+) pin of the power module which also feeds the "Radj" resistor of the UCC39002 application circuit as shown below. Are there any issues with utilizing the trim function when paralleling the modules as shown in the application circuit?

                  

  • 0
    TI__Mastermind 40070 points

    Hello Waseem, 

    Thank you for your interest in the UCC29002 Load-Share controller. 

    You raise a good question, and I am not aware of any design examples when using a module with a Trim pin function.  
    I think the answer to the question of issues depends on how the Trim function is implemented. 

    Your module is not identified, so I looked up a Synqor module with a trim pin. 
    Their datasheet implementation for Trim is not the same as your figure shows, but the basic concept is probably the same.  

    I assume that Trim is an optional function, but if your module's voltage must be trimmed away from nominal, then all modules should be trimmed the same.
    To provide current-sharing, the UCC29002 can only adjust a module's Vout upward.  It cannot adjust Vout down.  
    The ADJ pin current pulls the SENSE+ voltage down to do this.  In effect this is another "trim" operation, but a trim in a closed-loop control of output current in a multi-module system.   The Radj value is calculated to divert some of the available ADJ current away from the SENSE+ pin if the full ADJ current would trim Vout up too much for sharing.  

    I think the system design for current sharing is done the same way whether a Trim function on the module is used or not. 
    But if it is used, the main concern is to ensure that they are all Trimmed the same amount. 
    Also, be aware that the OVP threshold may be independent of Trim level, and the combination of maximum up-Trim plus maximum sharing adjustment may put Vout too close to the OVP threshold.   

    Regards,
    Ulrich