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BQ24105 Solar Charging

Kevin Stevens
Intellectual 350 points
Other Parts Discussed in Thread: BQ24105, BQ24650

I have a BQ24105 soldered into a PCB I designed according to the attached schematic. For the most part the charger seems to work fine when using a 12V battery as a supply (other than some charge termination concerns [see my other post for more details on that http://e2e.ti.com/support/power_management/battery_management/f/179/p/274388/1028282.aspx#1028282]).

However, when I connect a solar panel (~10V during testing) to the supply input, Stat1 and Stat2 are both high indicating a fault. If I put a multimeter on the nPG pin I see that the voltage is generally low, but it jumps around and seems to go high for short periods of time.

Measuring the current shows that only about 8mA of current is being drawn from the panel, so it is clear the charger is in a fault state and not charging.

What would cause this behavior? The solar panel has a Iid of 290mA and a Isc of 360mA. Having measured the current from the battery I do notice that there is about 500mA being drawn during charging. Is the fact that the solar panel is not able to produce this much current causing the chip to shutdown? I assumed I would just receive a slower charge if the input current was limited.

Is there any way around this, because I need to be able to charge from a solar panel?

02.Power.pdf
  • 0
    TI__Mastermind 31120 points

    I would try and use the bq24650 with a solar panel.

    One has to have some form of MPPT to pull the correct amount of power from the solar panel.

    a switcher typically pulls more input current as the input voltage collapses so once the solar panel is loaded beyond its MPP the solar source would collapse followed by the charger dropping out.

  • 0 in reply to Charles Mauney
    Intellectual 350 points

    Thanks for the suggestion. Two follow up questions though:

    1) Is there a way to do the MPPT tracking external to the charger chip so I can use what I already have in place?

    2) How would the bq24650 work with a non-solar input? What we need is a regulator that can handle input from a 5V USB source as well as a solar panel. Would the bq24650 be able to do both?

  • 0 in reply to Kevin Stevens
    TI__Mastermind 31120 points

    A1) Not sure what you have exteranally, but if your input to MPPT drops in voltage as the solar panel is loaded and once the solar panel reaches MPP the input signal to the MPPT drops to 1.2V.

     

    A2) The MPPT input is just a input voltage loop that once the input voltage drops to the reference voltage the duty cycle is held there keeping any further increase in output power (load).  If the input source is a low impedance device that can supply the needed load then the VinDPM loop does not kick in to regulate the duty cycle, the CC or CV loop is active regulating the output, deliverning all the required power to the load.