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BQ3050: bq3050 Internal Balancing

Sabrina Boeser
Prodigy 150 points
Part Number: BQ3050
Other Parts Discussed in Thread: BQ4050, BQ40Z50-R2

Hi,

we use bq3050 with Murata US18650VTC4 Cells in 3S1P pack.

For the balancing we only use the internal version that balances mupltiple cells at the same time, not with additional external FETs.

From our understanding measurements of cell imbalance are taken if Current is below Cell Imbalance Current (5mA) for Battery Rest Time (1800s)  and all Cell Voltages > Min CIM-check voltage (3000mV). It also sais that the measurements are taken "at rest". The balancing itself is then run during charging when Cell Voltage is higher than Cell Balance Threshold (3900mV).

Does this mean, if the battery is inserted in the host/application and is discharging while being used, that the imbalance measurements won't be taken?

So it could happen that during discharge the cells become imbalanced? But in this case if the imbalance measurements are not taken during discharge, could it happen that the packs are discharged down to 9,5V e.g. with cells showing 3,3V, 3,1V and 3,0V ?

We have Cell Imbalance Fail Voltage Threshold with only 300mV -> so we get a permanent fail in this case (difference > 300mV).

We were wondering if the imbalance permanent fail (VSHUT + CIM) coudl have actually occured during the application being used (discharging) ? Or if these PF would occur only during the time the pack is not used and "lying around (in relax mode), as the current is < 5mA then ?

Would be very helpful to hear from you.

Thank you very much in advance!

Sabrina

  • 0
    TI__Guru 52115 points

    Hi Sabrina,

    First of all,  bq3050 is a bit old device and I recommend you not use it for new designs and take a look at bq4050, which is the replacement for bq3050.

    Regarding your question,  we will take a look and get back to you.

    Andy 

  • 0 in reply to Andy Liu (BMS)
    Prodigy 150 points

    Hi Andy,

    thanks for your fast reply.

    My questions comes from an application that is already released and on the market since 2017, it uses bq3050. At that moment, when we developed this product, bq4050 was not completely released.
    So my question regards an issue coming from an already released product and hence, older design.

    That's why it would be great if you could still look into it and help us.

    For a new design that we started, we will use bq40z50-R2 with Impedance Track.

    Thanks,

    Sabrina

  • 0 in reply to Sabrina Boeser
    TI__Genius 10370 points

    Sabrina,

    Cell imbalance PF is only checked when the device is in "Relax" mode and the Min cell is above a specific voltage. Relax mode only occurs when you have minimal current on the battery (less than quit current). Since voltages vary a lot for minimal capacity different near empty it is recommended this "Check Threshold" should be at least 3.7V or higher. If you check at lower voltage you might get a premature tripping. 

    Thanks,

    Eric Vos