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BQ25756: Using 2 Charger in parallel

Silvan Sommer
Intellectual 320 points
Part Number: BQ25756
Other Parts Discussed in Thread: , TCA9543A

Tool/software:

Hello

Ones someone told me in this forum, that you can easily connect 2 of these BQ25756 Battery chargers in parallel to the batterypack to split up the charging current/load to both chips.

But now i was thinking wait a minute... This IC is just controlling a buck/boost converter to charge the batterys. But as i know now, it is not recommended to connect 2 different buck/boost converter together at the output? Because of voltage diffrences etc. 

So is this really a good idea to connect 2 Battery charger board at the output together and connect them to the batterypack to charge it? 

Thanks for your answer:) 

SIlvan 

  • 0
    TI__Expert 5445 points

    Hi,

    Two BQ25756 ICs can operate in parallel with themselves without communicating between each other. During fast charge, the BQ25756 acts as a current source, and current sources will add together in parallel. One BQ25756 should be set to a lower termination voltage than the other IC. This will let both BQ25756 ICs cleanly terminate charging the battery.

    Best,
    Michael

  • 0 in reply to Michael Bradbourne
    Intellectual 320 points

    hello

    Thank for the info.

    But why we have the problem by "normal" buck boost converter? ive read everywhere that you shouldn't connect 2 buck/boost's together at the output?

    And is there a way to change the I2C address of the chip so I can communicate with both at same bus? Or do I need a multiplexer?

    Thanks

    Silvan

  • 0 in reply to Silvan Sommer
    TI__Expert 5445 points

    Hi,

    Normal buck-boost converters will usually regulate to a voltage only. The BQ25756 is a battery charger that, for the most part, regulates current. This current regulation means that the charger is a current source, which can operate in parallel. When we intentionally set the termination voltage of one of the BQ25756 lower than the other, it will reach the CV mode of charge first. The lower termination IC will regulate the voltage while the other IC is regulating current. The lower termination IC current will decrease until it reaches termination where it will stop switching and turn off. This allows the other IC to raise the voltage to its termination voltage until its current decreases and charge terminates.

    There is no way to change the I2C address of the chip. The BQ25756E has a different I2C address, but it is a lower voltage device.

    Best,
    Michael

  • 0 in reply to Michael Bradbourne
    Intellectual 320 points

    Hello 

    Can I take the: TCA9543A from TI, to have separate buses? Then I can talk to each BQ25756 individually right? 

    My master is the OpenCR1.0 on which I wanna install Arduino software and control the I2C bus via Arduino libraries.

    Thanks

    Silvan

  • +1 in reply to Silvan Sommer
    TI__Expert 5445 points

    Hi,

    I am not an expert on the TCA9543A, but from reading the datasheet, this device seems to enable talking to each BQ25756 individually.

    Best,
    Michael