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BQ24765: BQ24765 to charge supercap

Emmanuel Roble
Intellectual 405 points
Part Number: BQ24765
Other Parts Discussed in Thread: BQ25713, BQ24130, BQ25710

I would like to ask why BQ24765 is not listed as supercap charger?

  • 0
    TI__Mastermind 25800 points

    Hey Emmanuel,

    While the BQ24765 can be used to charge supercapacitors, we don't recommend using this particular device to do so.

    There are several limits/clamps placed in the device that were designed specifically around Li-ion that are not ideal for high-current, super capacitor charging.

    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Intellectual 405 points

    Hi Joel,

    What alternative do you recomend then for 3s 7.5V total supercap with I2C/SMBUS control? We need to set the voltage via uC at will. The internal FETS also solves our footprint requirement.

    Can you give example of limits/clamps that can affect supercap charging? We only need to charge at around 3Amps max.

    Thanks,

    Emman

  • 0 in reply to Emmanuel Roble
    TI__Mastermind 25800 points

    Hey Emman,

    As an alternative, I would recommend the BQ25713 buck-boost charge controller. However as a controller it will require external FETs. What is your input voltage range?

    I was also informed you were considering using the BQ24130, which is a viable option as it's current limits are set a lower voltage setpoints.

    The limits I describe for the BQ24765 are the following as found in the EC table of the datasheet:

    1) VFB BATSHORT COMPARATOR. Below this threshold, the charging current is clamped to 220mA. 

    2) VFB BATLOWV COMPARATOR. Below this threshold, the maximum charging current is clamped to 3A. However, based on your comments, this would be acceptable for your application. 

    Usually, the biggest design constraint with supercaps is the ability fast charge them. A current clamp like the above will increase the charge time for the region where the supercap voltage is below the BATSHORT Comparator threshold.

    Re-evaluating your requirements, I believe either the BQ24130, BQ24765, or BQ25713 will work for you.

    Regards,

    Joel H


    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Intellectual 405 points

    Hi Joel,

    Regarding those limits, I read that those clamps are present also on both 25713 and 24130.

    Are those limits the only concerns? Because if my application wont let the capacitor voltage below 3V, I believe there is no more issues using BQ24765

    Regards,

    Emman

  • 0 in reply to Emmanuel Roble
    TI__Mastermind 25800 points

    Hey Emman,

    If your application won't let them the capacitors drop below 3V, then any of the above chargers will work fine.

    The other condition to consider is the first time charger, and even a scenario whether the capacitor is heavily depleted without an input source to charge. This would cause the capacitor voltage to drop below 3V. But if this is not a concern for your end use case, then again, any of the above chargers will work.

    One thing I would ask you to check is the input voltage range. If the charger must buck and boost the input voltage to charge the supercaps, I would recommend using the BQ25713.

    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Intellectual 405 points

    Hi Joel,

    Yes the application wont let it go below 3V. That is for the 3 capacitors in series. The initial charger is noted. Would you recommend a part for this purpose? My backup is to use digital potentiometer because selection of i2c/smbus enabled controllers is not that much.

    Thanks,

    Emman

  • 0 in reply to Emmanuel Roble
    TI__Mastermind 25800 points

    Hey Emman,

    Here I would say there is still not a great option as our chargers will have a clamp at these lower voltages.

    I would mention the BQ25710/BQ25713 again as an option as it is possible to place the capacitor directly at the system output of the converter (rather than at the battery connection). However, I have only tried this method as a proof of concept rather than a fully validated solution. 

    You are free to try it and validate the efficacy yourself; just let me know and I can provide some steps I used to implement it.

    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Intellectual 405 points

    Hi Joel,

    I would like to seek assistance again in my application. I now have a supposed to be working board of BQ24765 charger. My supercapacitor is precharged up to 6.5Vdc and trying to charge it to 7.5Vdc. The charger input voltage is set at 10V. Using the BQ24765 software with EV2300, the charge voltage is set to 7296mV, charging current to 896mA and input current limit to 2048mA. When im trying to charge the supercap, the BQ24765 charger input current suddenly increases to 2.5A+ then down to 180mA and the cycle repeats continuously at around 5sec interval.

    Do you  have a clue about my test results?

    Thanks,

    Emman

    C:\Users\Emman\Desktop\Act-20R (ATtiny 92519)\Act-20R (efm8 052819)

  • 0 in reply to Emmanuel Roble
    TI__Mastermind 25800 points

    Hey Emmanuel,

    Can you please post this as a new question specifically about the BQ24765 issue you are having? 

    It seems we resolved the product selection, so for tracking purposes we would like to close this issue out and open a new one regarding your most recent question. 

    We will link the new question post to this thread.

    Also, you document did not attach correctly.


    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Intellectual 405 points

    Hi Joel,

    Its ok, I just missed a connection.

    Thanks,

    Emman