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BQ51050B: Details on whether / what must change for 2020-era 15mm RX receive coil can work to charge small mAh coin cell batteries

Phil Liang
Prodigy 35 points
Part Number: BQ51050B
Other Parts Discussed in Thread: TIDA-00318, BQ25100

Reply back regarding TI details for changes to this Old 7+ Yr design to :

Details on whether / what must change for 2020-era 15mm RX receive coil can work to charge small mAh coin cell batteries

  • 0
    TI__Guru* 75656 points

    Hello

    The BQ51050B is optimized for 1A charging and will not work well at low current typically used for a coin cell.  Current regulation and termination accuracy are reduced.

    The TIDA-00318 is a better solution for low current charging applications.  This design is also compatible with parts and devices on the market in 2020.

  • 0 in reply to Bill Johns
    Prodigy 35 points

    Hello,

    Thanks for your reply but I need some advice on no more than 4.2V and 15mm RX coil (14.9 uH +/- 10% inductance, 1 ohm +/- 20%, Q=8.5 +/- 30%, # Turns = 30) for LIR 8mAh small cells.  What caps, resistors, and/or thermistor (if any) values to use?  Also, unlike Semtech NonQi ref design, is Vbat- (neg) = GND, here for TIDA-318 ref design schematic and Gerbers, while still providing Vbat+ (up to 4.2V if that charger is used, which one pre-charge or LED indicator), and SYSOUT (is this limited to a value (such as 3.3V in Semtech NonQi design)?).  thanks for your help

  • 0 in reply to Phil Liang
    TI__Guru* 75656 points

    Hello

    " I need some advice on no more than 4.2V and 15mm RX coil (14.9 uH +/- 10% inductance, 1 ohm +/- 20%, Q=8.5 +/- 30%, # Turns = 30)" --- Have you selected a coil and this is the specfications?  15mm is small and I recommend a larger coil and higher L value.

    "LIR 8mAh small cells" -- this is a small cell and will need charger configuration from TIDA-00318.

    "What caps, resistors, and/or thermistor (if any) values to use?" -- See TIDA-00318

    "Also, unlike Semtech NonQi ref design, is Vbat- (neg) = GND" --- Yes

    " TIDA-318 ref design schematic and Gerbers, while still providing Vbat+ (up to 4.2V if that charger is used, which one pre-charge or LED indicator), and SYSOUT (is this limited to a value (such as 3.3V in Semtech NonQi design)?). ---- The Charger output voltage will be up to 4.2V and current will be set by the ISET resistor.

  • 0 in reply to Bill Johns
    Prodigy 35 points
    Hello Thanks for reply with addtl info. have thoroughly studied BQ25100/1 charger series, and believe 25100 gives more prog term current given I don't need output digital active low to indicate In Charging state to MCU. But I Do Need 100% confirmation that the charger can stable provide Vbat (LIR small cell 8mAh) charging, while I simultaneously can Also use that same voltage to power and operate MCU rest of PCB. Pls confirm. 2. For my small cells, should I set current limit to smallest setting 10mA (fast charge), or can I possibly push it to 20mA (so 2.5X (capacity 8mAh))? Not sure what charge rate 0.5C, 0.2C, 1C mean in battery charge discharge specs (C is capacity?). I will plan for precharge in 25100 of 4mA and term of 2mA (specifying as % of Fast charge). So will set resistor values appropriately, and use 10kohm to GND to disable where thermistor in certain battery types might apply. For this signal, if you pull it directly down to GND, instead of through 10kohm resistor, does this Disable whole charging IC (so if anything goes wrong, I could force PCB to not waste batt quiescent current on the entire TIDA00318 system if not in a Qi field)? I also want to ask why the TIDA00318 schematic shows an input cap at 0.1uF C9, when spec description says between 1-10 uF (maybe affected by wireless IC side's caps?)? Haven't studied wireless Qi IC side yet, but pls advise on FOD and ILIM resistors, and any other config required for my Fixed 15mm diam RX receive coil whose inductance and other characteristics were stated. If you are able to contact me via direct email, please speak with Thomas Li who I am emailing. Thanks
  • 0 in reply to Phil Liang
    TI__Guru* 75656 points

    I am in contact with you and will work the question using PM feature of forum.