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BQ24650: USB-C battery charging compatibility

Ibrahim Qasim
Intellectual 680 points
Part Number: BQ24650
Other Parts Discussed in Thread: , TPS2121

Hello,

I just have an inquiry with regards to a possible addition of a USB-C port to charge my 4.2V Lipo battery at 5V. I followed the layout and schematic provided in the BQ24650EVM-639 with a few changes to match my solar panel's 6.3V MPPT voltage and and 4.2 V 1 cell battery. My issue is that I sometimes require a more stable voltage source during times of poor solar exposure.

I have noticed that Voltaic systems have designed their own version of a MPPT solar charger with the BQ24650 chip which includes a micro usb to charge at 5V by turning a knob potentiometer on the board itself to change the programmed MPPT voltage. Is it absolutely necessary to always make this change when connecting a 5V source to charge the battery? Also, with regards to the voltaic system's board, the USB should only be connected when the solar panel is disconnected and while that is fine, would there be a way for the chip to detect when charging from the USB source and switch to that instead of the solar panel voltage?

I have attached my schematic of the BQ24650 for the time being and was curious to see if there would be any issue if I connected a USB-C's voltage in pin at the Vin point between the D1 and TRS2 diodes found at the top of the schematic shown below.

Your feedback is greatly appreciated.

Thank you.

SolarCharger_Schematic_0-1_20200703.pdf

  • 0
    TI__Genius 10240 points

    Hi Ibrahim,

    The MPPT setting is input voltage DPM, which has to be lower than the input voltage for the charger to operate. The charge IC can't detect the input source. The other input can't be connected to Vin as the D1 is for reverse current blocking. Adding a power MUX is recommended.

  • 0 in reply to ezhao
    Intellectual 680 points

    Hello,

    Are you suggesting that I use a power MUX such as the TPS2121 to take as an input both my USB C output and solar panel output as they are and feed them into pin 1 (Vcc) of the BQ24650 chip?? If that is the case would my current supplementary circuitry in my schematic found at the Vsolar/Vin inputs be required at the input, output, or both of the TPS2121 chip?? I'm just confused as most battery charging chips I have worked with in the past contain a built in USB power pin that would switch the power sources internally.

    Thanks for your feedback!

    Ibrahim 

  • 0 in reply to Ibrahim Qasim
    TI__Genius 10240 points

    Hi Ibrahim,

    The charger you mentioned is likely to have a MUX integrated.

    A simple solution for this case is to add another Schottky diode with the second source and then connect to the Vin. The diode is needed to block the reverse current from the battery if the input terminal is accidently short to low impedance and it also serves as a MUX with D1. If the power loss or voltage drop on the diode is too high for the application, then an integrated MUX like TPS2121 is a good option. 

  • 0 in reply to ezhao
    Intellectual 680 points

    2235.SolarCharger_Schematic_0-1_20200703.pdfHello Eric,

    From my understanding, it seems that I should input my VBus voltage pin from my USB-C to the same point as my Vin after the D1 diode shown in the schematic below correct? In that case, would I be able to charge my battery simultaneously while my solar panel is connected to the system at periods of both low and high solar exposure? 

    It is important that a manual disconnection of the circuit is not needed in my application which is why I am adamant that my usb-c acts as my backup power supply when my solar panel is not performing.

    Would adding this extra source require me to readjust any of:my smoothing capacitors, Rsense, inductor, or MPPSET voltage dividers? 

    Thanks for your feedback!

    Ibrahim

  • 0 in reply to Ibrahim Qasim
    TI__Mastermind 24075 points

    Hi Ibrahim,

        The MPPSET divider is used to set to what the maximum powerpoint of your solar panel is. The risk in dual input situations for this device, is if the maximum powerpoint is higher than the secondary mains source. This is because when the mains is primary input, the input voltage regulation loop will try to regulate the charge current to push the input voltage above the MPPSET point, but as it is an adapter this is not possible and charge current would be 0.

  • 0 in reply to Kedar Manishankar
    Intellectual 680 points

    Hello Kedar,

    My mppset voltage is currently 6.29 V, so if I supply a 5 Volt usb input it will produce no charge current for the battery. Is there a way I can bypass this issue with the bq24650 chip, can i boost the voltage above the mppset point or is there a different chip i can use with the same features found in the bq24650 chip??

    Thank you 

  • 0 in reply to Ibrahim Qasim
    TI__Genius 10240 points

    Hi Ibrahim,

    The minimal operating voltage of the BQ24650 is 5V. Considering the voltage tolerance and cable voltage drop, this charger is not a good candidate for 5V USB input. Boost the voltage above the MPPT setting makes the solution complicated. We don't have standalone solution that can meet the requirements.