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Charging 13V Lithium Iron Phosphate with 12VDC source

Khoi Nguyen83
Expert 1180 points
Other Parts Discussed in Thread: BQ24650, TPS55340, BQ24616, BQ24610, BQ24620, BQ24773, BQ24630

I have used BQ24650 charging 13V LiFePO4 (Lithium Iron Phosphate) with solar power at Vmpp 17V on one design.

If I have 12VDC source power supply, is it possible to find similar charger or booster circuit to charge the same type of battery?

Or if we need crank the power supply to higher voltage like 14-17VDC to charge this battery.

I'm also looking at something like TPS55340 to boost 12VDC to 17V roughly for 2A charging current then drive the BQ24650.

This is only for charging the battery, and we will need to design the separate power path to drive load from primary 12VDC, with battery as backup.

  • 0
    TI__Genius 11480 points
    Hi Khoi,


    For this arrangement, I think you will need to boost the voltage first, and then use the bq24650 normally as you suggest. We currently do not have any buck-boost or boost chargers, like you would require for this application.

    Let me know if you need anything else!
  • 0 in reply to David Wiest Jr
    Expert 1180 points

    is the TPS55340 suitable for the 2A booster?

    Also do you have any application notes on power path to select primary 12VDC source then switch over battery as backup, then back to 12VDC when the primary source returns. We are driving a DC motor load of 15A continuous for few minutes, 30A peak <1s.

  • 0 in reply to Khoi Nguyen83
    TI__Genius 11480 points

    Hi Khoi,

    I think the TPS55340 will be suitable for this application. It seems to favor simplicity, low BOM, and has high enough current rating.

    Have you looked at the bq24610 or bq24616? These devices are in the same family as bq24650, and have similar functionality. They are a more "general purpose" charger with power path (the 616 is JEITA compliant, the 610 is not). These devices will do what you are asking automatically.

    However, these are the app notes that I found:

    http://www.ti.com/lit/an/slua400/slua400.pdf

    www.ti.com/.../slua376.pdf

  • 0 in reply to David Wiest Jr
    Expert 1180 points

    We are using LiFePO4 battery. Is there an equivalent charger for it with power path control?

    maybe BQ24620, BQ24630 or even BQ24773 since we have I2C capabilty as well?

    Ideally, if we could just re-use the BQ24650 since we have that working, that would be great and add the option for 12V booster in front.

    That way we can use the same board with stuffing option for both solar application and 12VDC source .

    The power path design might need more work, but doable looking at your appnote links.

  • 0 in reply to Khoi Nguyen83
    TI__Genius 11480 points
    You are correct, the bq24620 and 630 are the same core as the bq24650, and is what you would want.

    If you want to stick with the bq24650, there are some workarounds. If you look at the bq24650 EVM, they actually make a "Pseudo powerpath" by using a schottky diode to separate battery and the system load. Your efficiency will be slightly less because of the diode drop, though. You can also modify the feedback resistor divider, since the bq24650 has an adjustable output voltage. You use the equation:

    Vout(reg) = 2.1*(1+ Rtop/Rbottom) , with Rtop being the resistor from Vout to Vfb, and Rbottom being the resistor from Vfb to ground
  • 0 in reply to David Wiest Jr
    Expert 1180 points

    Also for future proof, can we tune the BQ24650 or 620/630 to charge small gel cell battery?

    like MK battery AGM or Gel Cell battery

    MK_SmallSealed_v4r7.pdf

  • 0 in reply to Khoi Nguyen83
    TI__Genius 11480 points

    Hi Khoi,

    It looks  like those are lead acid batteries? If so, the bq24650 is definitely  capable of charging them. This app note explains how to do it: http://www.ti.com/lit/an/slva437a/slva437a.pdf