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BQ29209: BQ29209 cell balance circuit doubts

Part Number: BQ29209
Other Parts Discussed in Thread: , BQ25882

Hi,

first of all, I'm sorry for my poor experience about battery management  circuits.

I have to put in series two Li-ion batteries (3,7 to 4,2) in order to get more voltage from them. I focused on the BQ29209-Q1 but I have some doubts about it  I hope you can clarify:

  • Is the Bq29209 also a battery charger or just a device which takes care of unbalancing issues ? If not , is any battery charger suitable? 
  • From the datasheet I see that there is an external network to do if the automatic confguration cant make its job. How can I Know  if I have to design the external network or keep the automatic configuration ? 
  • From the datasheet , the recommended VDD is 10V. Can I use 12Volt coming from another big battery on its input?  If not could you suggest an LDO in order to get 10V on output (current rating) ?

Hope you can help.

Thanks in advance for your support.

Nico

  • Hello Nico,

    bq29209 is not a charger device, it is a 2S battery secondary protection IC with cell balancing. To charging the 2S battery, what's your input voltage and what your charging current required ?

    The recommended range of VDD from 4~10V. Generally, the device is powered by the the cells that connected to the device.

    For your secondary question, do you mean the how to make automatic balancing with external balancing circuit for higher current or the external circuit to control the CB_EN pin.

    Thank you,
  • Hi Jessica,

    thanks for quick reply. I'm a bit confused, sorry.

    I have understood now that the bq29209 is just for balancing issues.

    I also understood the dvice is directly powerd from the voltage serie (for me about 8 volt). Is this a problem? 

    I have to charge these 2 batteries : https://it.rs-online.com/web/p/batterie-al-litio-ricaricabili/1445691/  so the voltage serie never gets 10V reccomended.

    From what I see on google I should  design a circuit which charges these 2 batteries  in parallel and then switch to a serie configuration when they are charged (may be by using a physical switch to pass from parallel mode to serie mode ). Am I right ?

    Then, when the circuit switches to serie mode I have to include the balancer bq29209 . Right ?

    The other question is : do I have to use the external configuration (like in figure 12 of the datasheet) or just using the normal configuration (Figure 10) is good ?

    Hope you can help,

    thanks again.

    Nico

  • Hello Nico

    It's okay to power device with your battery.

    For the circuit design, it depends on your required balancing current. If you need the balancing current above 15mA, need use the circuit like figure 12. Higher balancing current could reduce the balancing time, but it also introduce extra thermal in the circuit.

    I would suggest you keep the device in series for charging and discharging, the system will be more simple.

    For the charger selection, you could check for the 2S charger solution on ti.com. Generally, if input voltage is 5V, boost charger bq25882 can be used. if the input voltage is always higher than the battery voltage, you could select the buck charger based on your charging current requirement.
  • Hi Jessica.
    Thanks a lot for the support.
    It's clear now.