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Battery charger for solid state lithium thin film batteries

John Griffith
Mastermind 21768 points
Other Parts Discussed in Thread: BQ25155, BQ21061

ST Micro - EnFilm efl700a39.pdf

Hello,

Are there any specific chargers that would be better for solid state lithium thin film battery like the EFL700A39 that I have attached? I have never worked with these batteries and am trying to understand if there are any things I need to be aware of for these applications. 

Thanks!

John

  • 0
    TI__Mastermind 19195 points

    Hi John,

    This cell follows 3V-4.2V CC/CV charging like li-ion but at a much lower charge current, from the spec looks like Ichg = 1mA and termination at 100uA. Our closest charger for this would be BQ21061/BQ25155 which supports down to 1.25mA Ichg / 500uA Iterm.

    Best regards,

    Nick

  • 0 in reply to Nick Brylski
    TI__Mastermind 21768 points

    Hi Nick,

    Thanks for the quick response! I agree, the taper current looks to be 100µA, but the datasheet does say:

    Battery can be charged from a 4.2 V ±0.05 V constant voltage source with or without current limit. More than 90% of the total capacity is recharged when the charge current falls below 0.1 mA.

    This seems to imply the 1mA isn't a hard requirement and it also seems to state that the typical constant current, followed by constant voltage that standard lithium ion batteries use isn't necessarily needed, right? Will our devices automatically switch between charging CC and CV modes? 

    John

  • +1 in reply to John Griffith
    TI__Mastermind 19195 points

    Hi John,

    Yes they don't list a max charge current limit so likely could charge higher than 1mA and be fine. With just CC charging you could get 80% of max capacity, 90% with a CV taper to 100uA. 

    Best regards,

    Nick

  • 0 in reply to Nick Brylski
    TI__Mastermind 21768 points

    Hi Nick,

    Thanks! That helps, and it sounds like the charger will shut off after the current drops under 100µA which means the last 10% will never get charged. I am all set on this for now. 

    Thanks again,

    John