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UC3907: load sharing

switch
Genius 3710 points
Part Number: UC3907
Other Parts Discussed in Thread: UCC29002

Tool/software:

Hi ti team，

For the new project, we intend to use the UC3907 for load sharing, and design two 24V/3A POE power supplies to power a 24V/6A load.

Could you please advise on how to ensure that each of the two POE supplies delivers an average current of 3A? Are there any reference circuits available? (As shown in the block diagram below

  • 0
    TI__Mastermind 40120 points

    Hello Switch, 

    Thank you for your interest in load-sharing controller by TI. 

    The UC3907 is an old device made entirely in bipolar technology, and contains reference and feedback circuitry to be used for regulating the power supply. 
    If you plan on designing each POE supply discretely, then this device can work for you. 

    Limited technical support documentation can be found here: https://www.ti.com/product/UC3907#tech-docs 

    If you already have two previously-designed POE modules that you want to share the load with, then I recommend to use the UCC29002 controller, which is much simpler and newer.  It is made in BiCMOS technology for lower cost. 

    Extensive technical support documentation for this part can be found here: https://www.ti.com/product/UCC29002#tech-docs 

    Regards,
    Ulrich

  • 0 in reply to Ulrich Goerke
    Genius 3710 points

    Hi  Ulrich，

    The VDD voltage of the UCC29002 does not support 24V, and its maximum voltage is 15V. May I ask if we should use a voltage divider resistor to reduce the VDD voltage to within 15V?

  • 0 in reply to switch
    TI__Mastermind 40120 points

    Hello Switch, 

    The UCC29002 can accomodate sharing voltages higher than 15V by using its internal clamp (~13.5V).

    A single resistor is all that is needed to drop the ~10V needed between 24V output and 14V VDD level. 

    This Excel-based Calculator Tool can help select the appropriate resistor value, as well as the overall design: https://www.ti.com/tool/download/SLUC684 

    Regards,
    Ulrich