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BQ76930 - high current (2A) balancing circuit

Michal Radziwon0
Prodigy 145 points

I am designing 8 cell LiFePO 20Ah battery management system, where speed of charging is one of the major points.  Therefore, I am in need of pretty decent balancing current of at least 1-2A.

Devices suggested in datasheet for external cell balancing (such as DMN2004DWK, NTZD3154N, and Si1024X) are ll rated below 1A. Could I ask you for a support in choice of balancing FET for such system?

  • 0
    TI__Mastermind 23116 points
    Hello Michal,
    Most of your power dissipation will be in your resistor used to do balancing. Selecting a FET and resistor depends on a variety of things. The main consideration will be how you manage your power dissipation? Fan? Conductive cooling, natural convection, heat sink? what is your operating environment? You can use either an N-channel or P-channel fet to do balancing but most use N-channel. Calculate your power dissipated in the FET (I^2*Rdson at temp) and make sure the package can handle it given the operating environment. With such high balancing currents, have you considered active balancing? It is much more efficient and balances faster, though it is more complex and more expensive.
    -Francis Houde
  • 0 in reply to fhoude
    Prodigy 145 points
    Thanks a lot Francis.

    I do plan to have a passive cooling with heatsink. I especially appreciate suggestion about active balancing, however, as you have also mentioned, it starts to be pretty expensive.

    Close inspection of parts suggested by datasheet shows some extra protective diodes, and I would like to identify a transistors with the same functionality, just rated for higher current and higher power dissipation, maintaining a low threshold voltage (required to be ~1.5V for LiFePO cells). Could you throw some suggestions on me?