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BQ76PL455EVM: Power supply and cell balancing

Alexander Hernandez
Prodigy 90 points
Part Number: BQ76PL455EVM

Hello, 

In regards to the power supply, what happens when there is excess power in the cells and the connected power supply(12V) isn't enough to store the excess power? Also what happens in a reverse situation where the power supply doesn't have enough energy to completely balance the cells? In the latter case do the cells get balanced to a lower capacity or are they left half balanced? Also If the boards are daisy chained does one board take priority over the others or do they all share the power supply equally in a limited power situation?

Thank you,

Alexander

  • 0
    TI__Genius 11480 points
    Hi Alexander,

    I'm afraid I'm having troubles understanding your scenario. Could you provide a diagram?

    The pl455 is powered from the cells it monitors. Balancing is also done passively - it turns on a MOSFET with the EQ pin, which dissipates energy through a resistor. There is no balance transferred.
  • 0 in reply to David Wiest Jr
    Prodigy 90 points
    Hello David,

    My apologies, I meant to reference a board with active balancing such as the TIDA-00817. My question is in regards to the external battery connected to the stack to charge and hold the excess charge of the cells. Where does the excess charge go if a charged 12V external battery is connected to a stack that is overcharged. Say all the cells are at 4.4V and their set max voltage is 4.2V. Will it send this energy to the already full external 12V connected to the stack? I hope this clears up the confusion.

    Thank you,

    Alexander Hernandez
  • 0 in reply to Alexander Hernandez
    TI__Genius 11480 points
    Hi Alex,

    Typically, I have not seen someone run into this situation. If this is the case, however, then either the cells or the 12V will need to be bled off a little to handle the balancing current.

    Typically (as is the case with TIDA-00817) there will be external OV/UV on the 12V battery that will halt the balancing as well, in which case no transfer will occur.