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Battery Charger

Ray Vincent Aranzaso
Mastermind 18180 points
Other Parts Discussed in Thread: BQ25570

Hi,

Good Day.

The customer is looking to charge a small battery with a standard current of 5mA. Is this possible with any of our ICs? Are they configurable or is it possible to adjust them using external circuitry?

The application is to harvest a piezo or magnetic energy harvester to charge a small solid-state battery.

Please advise. Thank you very much.

Best Regards,

Ray Vincent

  • 0
    TI__Guru**** 166896 points

    Hi Ray,

    The piezo or magnetic harvester has a high impedance output and most likely rectification.  So, you will need a charger with VINDPM (MPP).  What  the MPP and open circuit voltages as wells max output current expected at MPP?  

    Regards,

    Jeff

  • 0 in reply to Jeff F
    TI__Mastermind 18180 points

    Hi Jeff,

    Good Day. Please see below the response of our customer to your reply. Thank you very much.

    From the piezo at our maximum excitement, we have seen 180uW, current 27uA, and 6.3 volts.

    To charge the batteries, we need 4/5mA at 2.6V.

    We are limited to what level we can characterize atm in terms of rotation speed.

    Best Regards,

    Ray Vincent

  • 0 in reply to Ray Vincent Aranzaso
    TI__Guru**** 166896 points

    Hi Ray,

    If the 6.3 V is the MPP of the piezo after rectification, then we don't have a good solution.  

    If not, after rectification to a dc voltage, a piezo source typically has MPP = 40-50% of VOC or MPP~=3.15V.    The only option we have is the BQ25570 boost based charger with integrated buck converter.  Since its input voltage, VINDC, has abs max of 5.5V, a zener clamp of 5.5V on VINDC is required.  The regulated output of the boost converter, VBAT_OV, needs to be set slightly higher than MPP=3.15V for the boost converter.  The storage element needs to be connected to the output the BQ25570 buck converter, VOUT, set to 2.6V instead of VBAT.

    Regards,

    Jeff