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BQ24650 with no battery

Craig Stephan65
Prodigy 30 points
Other Parts Discussed in Thread: BQ24650

1. Does the device require a battery to operate? Can I operate the circuit with just a single 6V panel and connect the PH output (through the suggested inductor and resistor) to the board's DC-DC regulators.

2. I have the PH output net (through the suggested inductor and resistor) tied to some downstream voltage DC-DC regulators. The charge circuit status does not indicate that I do not have a battery installed when I remove the Li-Ion battery. Is this normal, considering that there is still a load on the output of the charge controller?

  • 0
    TI__Expert 8690 points
    Hi Craig,

    The device needs a battery at SRN in order to work (battery detection). You can also trick the part into thinking there is a battery by connecting a 5mF cap at SRN.

    If you have the system connected at the SRN node, it will continue to draw current as long as the device has previously detected a battery. If you remove the battery but still have a load, the converter may not stop, this is the same behavior on the bench.

    Regards,
    Steven
  • 0 in reply to Steven Bangdiwala
    Prodigy 30 points
    I have the BQ24650 connected to a single Li-Ion cell. The input is connected to a 6V/2W solar panel. If I install a fully discharged battery and put the solar panel in direct sun, will the bq24650 turn on and charge the battery?
  • 0 in reply to Craig Stephan65
    TI__Expert 8690 points
    Craig,

    Yes, the device should be able to charge it, assuming you have set the correct resistor divider for MPPSET based on your panel datasheet.

    Regards,
    Steven
  • 0 in reply to Steven Bangdiwala
    Prodigy 30 points

    Steven,

    Thanks for the reply. I have a question about setting the resistor divider for the MPPSET input. Are there any negative implications for setting the resistor network so that the charger is on when the panel voltage is at 4.5V. For example, if I set the MPPSET to be equal to 1.2V when Vpanel equals 4.5V, would there be any harmful effects?

    Our current circuit has a resistor network of 82K and 330K to set the MPPSET input to 2.1V when the panel voltage is at 6.0V. Under load, the panel's voltage dips to 5.5V and below, and I would like to use this little wattage to charge the battery slowly. Our batteries are li-ion that charge at 4.2V.

    Thanks,

    Craig

  • 0 in reply to Craig Stephan65
    TI__Expert 8690 points
    Craig,

    It is better if you leave the solar panel regulation at the MPPT of its datasheet. If you lower MPPT to 4.5V, not only does your solar panel power output drop, the charger cannot operate at this condition. It has a sleep comparator where your VCC should be at least 650mV above VBAT. (VCC>SRN+650mV for guaranteed operation).

    Regards,
    Steven