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Original question:

BQ24650: BQ24650RVAT: Maximum Charge Current

BQ24650: charge current 30A

tony gima
Prodigy 20 points
Part Number: BQ24650

Hi,

I am designing a solar charger for 1s 18650 lithium battery for a gateway sensor. The calculated current for the batteries to be charged within 3.1 hrs of sunlight, autonomy of 7 days is around 30A. The nominal voltage for the battery is 3.7V and I need 30 batteries in parallel for it to supply voltage to the sensor. Is bq24650 is capable of supplying the current and can be used to charge the batteries for this design?

Tony

  • 0
    TI__Mastermind 24075 points

    Hi Tony,

    1.  30A charge current is very high for BQ24650. The reason we spec it for 10A even though it is a charge controller, is due to the limitations of the internal gate drive strength that is used to drive the switching FETs. For 30A the FET required should be larger to account for the increased current which results in a higher Qg of the FET. As these FET are driven at the 600kHz switching frequency, this would result in large gate drive losses which are not feasible. 
    2. ACP-ACN and SRP-SRN max differential voltage is 100mV, normally 10mOhm for 10A max, 5mOhm can support 20A max etc.
    3. The issue with paralleling multiple BQ24650 to achieve 30A, is during termination, as the Constant Voltage loop of the different BQ24650 IC will try to regulate the same output.
    4. For 30A layout is extremely critical as well.

    One possible solution is to use an external gate driver to boost the internal gate drive strength and reduce gate driver losses, provided the input voltage is within recommended operating conditions of BQ24650. We do not have a reference design for such a system, and have not evaluated this solution so support is limited.

  • 0 in reply to Kedar Manishankar
    Prodigy 20 points

    Hi Kedar, 

    Thank you for the feedback. I am planning to parallel bq24650 and reduce the current to 20A, based on what you said, I will still have an issue with constant voltage loop trying regulate the current. With your suggestion of adding an external gate driver? is there any similar designs that I can have a look at to give me some ideas on how to implement it in my design? I was thinking of just changing the Rsr resistor to get the 30A should be ok for what i'm doing.

    Thank you again, hope to hear from you soon.

    Regards,

    Tony

  • 0 in reply to tony gima
    TI__Mastermind 24075 points

    Hi Tony,

       Unfortunately we do not have any reference designs for such a system as mentioned above. You can evaluate with just changing the resistor, however the main issue is the power dissipation, as careful consideration has to be given regarding layout. The EVM most likely cannot just have its RSR changed to achieve this 30A charging.