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Integrated Wireless Charger receiver for 0.35mA/4.2V Li battery

Kim Ash
Prodigy 100 points
Other Parts Discussed in Thread: BQ51051B, BQ51050B, BQ25100, BQ51003, TIDA-00318, BQ25120

Hi,

I am looking forward to charge a Li battery with constant current 0.35mA and constant voltage 4.2V. I found BQ51051B as a potential integrated charger. It supports a Charging Current up to 1.5 A. However value of KILIM is not mentioned for current 0.35mA. May I know what value shall I use for that. Or is there a better integrated wireless charger receiver for the battery.

Thanks 

Kim

  • 0
    TI__Genius 14890 points

    Kim,

    The bq51051B has a Charge Regulation voltage of 4.35V. The bq51050B is set to 4.2V.

    At 350mA, the KILIM distribution will be a bit wider than the 303-321 shown in the datasheet.  But, the equation is still the same. 

    For 350mA, set the resistance (RILIM) to 314/0.35 = 900 ohms.  That includes the resistance between ILIM and FOD plus FOD to ground. 

    As you evaluate your design, you may see the actual current vary a bit more than 3.5%.  Functionality is still solid.

    Regards,

    Dick

  • 0 in reply to Dick Stacey
    Prodigy 100 points

    Dear Dick,

    Thanks for the reply. There was a typo. The battery is meant to br operated at 35mAh.

    Can you update me with the values in this range.

    Thanks

    Kim

  • 0 in reply to Kim Ash
    TI__Genius 14890 points

    Kim,

    If you are going to charge at 35mA, I would suggest a combination of the bq51003 plus the bq25100.  Please look at the TI Design TIDA-00318.  It is an implementation of that solution.  

    The key to the bq25100 is its very accurate charge termination at low currents.  The bq51050B is targeted towards higher current solutions so it is optimized for that 4 to 5W area.  The termination accuracy for the bq51050B is not as precise as the bq25100.

    Regards,

    Dick

  • 0 in reply to Dick Stacey
    TI__Expert 4600 points

    Depending on your system requirements, you may want to consider a more integrated charger such as the bq25120.  This device has a very programmable linear charger, plus low-Iq DC/DC converter, plus LDO, plus push-button controller with reset function.  There are two reference designs with low power wireless charging and the bq25120:

    http://www.ti.com/tool/PMP11311  and http://www.ti.com/tool/TIDA-00712

    Regards,

    Steve

  • 0 in reply to Steve Schnier
    Prodigy 100 points

    Dear Steve and Dick,

    Thanks! I did consider both the designs but I am looking for an integrated wireless charger+receiver for the given specifications.

    Regards

    Kim

  • 0 in reply to Kim Ash
    TI__Genius 14890 points

    Kim,

    What can you tell me about the volumes of this design?  If it is a limited quantity, then using the bq51050B would work as you could evaluate each system.  On a large build, you should expect to see wide variation of the termination current.

    Regards,

    Dick

  • 0 in reply to Dick Stacey
    Prodigy 100 points
    DearDick,
    I am looking to limit the design area in 20-25mm range. I checked bq5105b, the value of KILIM is not specified for 35mA range. But t does say it works till 1.5A. What value should I be considering to operate at 35mA.

    Thanks
    Kim
  • 0 in reply to Kim Ash
    TI__Genius 14890 points

    Kim,

    The formula is still the same:

    ILIM = KILIM / RILIM or RILIM = KILIM / ILIM

    To set at 25mA, use:

    RILIM = 314 / 0.025 = 12,560 ohms.

    As noted in a previous reply, the charge current and termination current will vary from part to part beyond the range for 500mA - 1500mA.

    If you are doing a large quantity, the bq51050B is not a good solution.

    Regards,

    Dick

  • 0 in reply to Dick Stacey
    Prodigy 100 points

    Hi,

    Can you please verify my design for charging 35mA battery at 4.2V using BQ51051B.

    Thanks

    Kim

  • 0 in reply to Kim Ash
    TI__Genius 14890 points

    Kim,

    The capacitor on COM1 shows 0.0022uF and it should be 0.022uF (as in COM2).

    Charge Current is set to 35mA as you desired.

    Termination current is set to 3.5% of charger current, or 1.2mA. Please see the "Termination Calculations" section for other options.

    As noted in previous posts, this solution will not be consistent over a large build.  Charge current and termination current will vary.

    Also, the bq51050B has a regulation voltage of 4.2V while the bq51051B has a regulation voltage of 4.35V.

    Regards,

    Dick

  • 0 in reply to Dick Stacey
    Prodigy 100 points

    Dear Dick,

    Thanks for verification and suggestion. I will take them into account. Also is there any software where I can simulate and test the battery performance with the charger and receiver.

    Thanks

    Kim

  • 0 in reply to Kim Ash
    TI__Genius 14890 points

    Kim,

    We do not have any software for battery and charger emulation.

    Regards,

    Dick

  • 0
    Prodigy 100 points
    Dear Dick,

    I am working on BQ25100 and BQ51003. However while designing the prototype I am having problem with the package. I am using EagleCAD for layout. I am using the minimum via size as 0.2mm and track width of 0.127mm. It is becoming impossible for me to route pins in the centre of the IC. Can you suggest me an alternative.

    Thanks
    Kim
  • 0 in reply to Kim Ash
    TI__Genius 12475 points

    Kim,

    It is almost impossible to route through the center balls to cover all the pins. I highly recommend to use VIA fill on the BQ51003. 

    You are looking at a 10mil via with a 6mil hole on it. The vias will have to be plated shut and planarized as well. On the BQ25100 you shouldnt have issues. 

    Regards,

    Gautham.

  • 0 in reply to Gautham
    Prodigy 100 points

    Dear Gautham,

    Thanks for replying. I couldn't really get what you meant by via fill. Could you elaborate that please? I am having issues only with BQ51003. It would be really helpful if you could suggest some links or references related to that.

    Thanks

    Kimwireless charger1.pdf