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BQ24075: Possible Batteries as well as Fast Charge current MIN

Anthony Shilly
Prodigy 40 points
Part Number: BQ24075
Other Parts Discussed in Thread: BQ25120A

Hello,

I was wondering what type of batteries are typically used with this chip.  Is it possible to use this chip with small Li-Ion batteries for example ML1220 (17 mAh Capacity) (Standard charge is 1.2 mA)?  Like would it be possible to lower the Iset current lower than 100mA to reach this value ?  Or is this chip only designed to be used with bigger applications?  We are trying to use it in a wearable device Application.

Thanks in advanced.

Anthony Shilly

  • 0
    TI__Genius 11850 points
    Hi Anthony,

    As you said, the minimum fast charge current for the bq24075 is 100 mA.
    I would recommend looking into the bq25120A instead. It is a good choice for low current, wearable applications. The fast charge current range is 5-300 mA, and it also includes features found on the bq24075, such as power path, Vindpm, and temperature monitoring.
    Would that work for your application?

    Best Regards,
    Angelo Zhang
    Applications Engineer | Battery Charging Products
  • 0 in reply to Angelo Zhang87
    Prodigy 40 points

    Awesome that helped out a lot, we're actually going to go ahead and use that chip you suggested.  I had two more questions if you don't mind addressing.

    1. What is a good fuel gauge chip to go along with the chip you mentioned for battery charging?

    2.  Also do you know what type of batteries would best go with those chips for a wearable application? Ex Smart watch. (low profile)

    Thanks in advanced,

    Anthony Shilly

  • 0 in reply to Anthony Shilly
    TI__Genius 11850 points

    Hi Anthony,

    Glad to hear that you can use the bq25120A in your design!

    In regard to your other questions, here's a thread which may be helpful to you. There's a link to a TI reference design for a smartwatch in that thread which combines the bq25120A charger with the bq27421 fuel gauge.
    e2e.ti.com/.../471607

    Section 1.6 in the design guide from the above link also discusses the best choice of battery for this application. To summarize, any rechargeable Li-ion battery cell can be used, but since the bq25120A's max charge current is 300mA, it's better to choose a battery with a cell capacity of about 300 mAh (this is typical for wearable device applications). Here's a quick Mouser search to get you started:
    www.mouser.com/.../N-5gbk

    Best Regards,
    Angelo Zhang
    Applications Engineer | Battery Charging Products

  • 0 in reply to Angelo Zhang87
    Prodigy 40 points

    Hello again I have one more additional question regarding the bq27421 fuel gauge you recommended.

    Is this fuel gauge limited to battery capacity?  For example we are planning on using a 15mAh battery and we weren't sure if that specific fuel gauge chip can only give accurate measurements for a certain specific range of Capacities.  Is there a capacity limit? and if so how are you able to know that?  We looked through the datasheet to see if there was some specific parameter that shows this limitation (if there is one).

    Thanks,

    Anthony Shilly

  • 0 in reply to Anthony Shilly
    TI__Genius 11850 points
    Hi Anthony,

    The battery capacity range for the bq27421 gauge is 100-8000 mAh. This can be found in the parametrics table on the product page: www.ti.com/.../BQ27421-G1

    You can also use the search tool here to filter out gauges based on their minimum battery capacity. Unfortunately, the lowest minimum battery capacity for TI's Li-ion battery fuel gauges is 100 mAh.
    www.ti.com/.../products.html

    Is the 15 mAh requirement flexible?

    Best Regards,
    Angelo Zhang
    Applications Engineer | Battery Charging Products