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UC3907: UC3907: circuit review,LOAD SHARE CONTROLLER

KIM Andy
Expert 2530 points
Part Number: UC3907
Other Parts Discussed in Thread: UCC39002

HI

requesting a circuit review for the UC3907.

When the output load current is 2.5A, when two SMPS are LOAD SHARE, each output current is measured as 1.35A, 1.15A.

How can reduce the two output current deviations?

Circuit configuration is as follows.

  • 0
    TI__Genius 9790 points
    Hi, Andy
    Thanks for your interest in TI here. I've contacted the appropriate product group. You should hear from them soon.

    Regards,
    Yunsheng
  • 0 in reply to Yunsheng Qu
    TI__Mastermind 34465 points
    Andy,
    You are getting a +/- 8% load sharing tolerance at a nominal 1.25A from a 27A power supply.
    That is a very good tolerance an you will most likely be unable to achieve a better result.
    The main reason for this is the 5mOhm sense resistor.
    At 1.25A the sense voltage is only 6.25mV so pcb layout and noise pickup is going to cause an imbalance.
    Load sharing is usually important only at max power. Is there some special reason you require a tight tolerance load share at very low power ?

    Regards
    John Griffin
  • 0 in reply to John Griffin1
    Expert 2530 points
    HI

    thank you for the reply.

    Output currents of 15.1A and 11.9A were confirmed under load conditions of 27A under the applicable circuit conditions.
    I want to improve it even at max power.
    Is it possible to reduce the deviation of the two current values by selecting different sense resistors?
    Which part of the noise should be improved?
  • 0 in reply to KIM Andy
    TI__Mastermind 34465 points
    Hi Andy,
    You should consider using the UCC39002 load share controller.
    It has a better than 1% load share accuracy compared to 1.25% for the UC3907.
    Its current amplifier can be set for high side or low side sensing and it has a better common mode rejection ratio.
    Also it is in an 8 pin package.
    Regards
    John