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BQ24650: Vbat, Vmppset and other questions

SAB
Intellectual 950 points
Part Number: BQ24650

I am using a 12.8V LiFePO4 battery.  I see that "For maximum cycle life, the end-of-charge Voltage threshold could be lower to 4.1V/cell".  How do you set the end-of-charge Voltage threshold?  I am assuming that the Vbat (charge Voltage) should be 4.2 * 4 = 16.8. Vmppset = ?????  It also appears that Iprecharge and Iterm is the same thing?  Suggestions?  Thanks.

  • 0
    TI__Guru**** 166626 points
    The 4.2V/cell is assuming the charger is charging a LiIon battery. LiFePO4 is 3.6V/cell. With 3 cells, you will set VFB resistors for 12.8V battery regulation voltage.

    The BQ24650 is intended to be used with high output impedance source, like a solar panel. Solar panels have a maximum power point (MPP) that is usually ~80% of their open circuit voltage. The MPP feature of this charger allows you to configure the charger that it pulls current for its source only until the sensed input voltage through the MPPSET resistors is at the desired MPP point. IPRECHARGE and ITERM are 10% of the ICHRG setpoint.

    Below is a link to a spreadsheet that will help you size the components. Be sure to select the correct tab at the bottom for the BQ24650.

    www.ti.com/.../sluc175
  • 0 in reply to Jeff F
    Intellectual 950 points
    The spreadsheet really helps me understand the data sheet a lot better. I am using a solar panel but am confused on how to find the "desired MPP point"?
  • 0 in reply to SAB
    TI__Guru**** 166626 points
    Your solar panel has a VOC and ISC rating. MPP is typically ~80% of VOC. The solar panel datasheet should provide some info. If not, you may need to characterize the solar panel.
  • 0 in reply to Jeff F
    Intellectual 950 points
    That answers all my questions as right now. Thanks.