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BQ25750: As a solar battery charger

Teun Noordkamp
Prodigy 50 points
Part Number: BQ25750

Tool/software:

Hello there,

I am currently designing a circuit that will use the BQ25750 as a solar battery charger. If I am using the typical circuit from the datasheet (page 62) and made the Vin window as big as possible, lets say 4.5V-30V, this would result in the problem that the system voltage could be the same as the same as Vin. Thuss Vsys could get 4.5V.
I figured to overcome this problem I should remove the BATFET and get the Vsys directly from the battery (read battery side of BATFET).

According to the datasheet the sys pin is only an input pin and will measure the system voltage to control the BATFET or it will control the buck-boost circuit in reverse mode.

So my questions are:

  • Is my thinking of the circuit correct? (Yeah I know that a solar panel could be seen as a current source so, the voltage would get high very quickly. So I could made my Vin window smaller, but I measured a voltage of around 7V on a cloudy day with no load attached using a 30Wp solar panel)
  • Do I still need to connect the sys pin of the BQ25750 in this case?
  • If I need to connect this pin to what, do I need to connect it?
  • Should I connect it to ground, to my Vsys from the battery or behind Rac just as in the typical circuit?

I hope someone could help me further?

Kind regards,

Teun

  • +1
    TI__Mastermind 30745 points

    Hello Teun,

    1. Yes, I think this setup is good. With the system load in parallel with the battery, you won't have to worry about the solar panel's output power being overloaded.

    2. Yes, you still need to connect the SYS pin.

    3 and 4. Connect the SYS pin behind Rac like the typical circuit.

    Let me know if this makes sense and let me know if you have any more questions.

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Prodigy 50 points

    Hi Ethan,

    Thank you very much for you quick response, you answer helped me a lot.

    Kind regards,

    Teun Noordkamp