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BQ27426: BQ27426 reverse capacity and averaging GG

Katsuhiro Kanao
Intellectual 1710 points
Part Number: BQ27426

HI Team

My customer

 

  1. Reserve capacity.

My customer want some margin for GG.

For EX, set the system voltage 3.0V, reserve capacitance is 100mAH.

They hop SCO=0% at 100mAH.

Is it possible bq27426 ?

 

 

  1. SOC averaging.

Is it possible that controls the SOC update speed by control of GG?

They want to know if there are some command to control update timming ?

 

best regards K.Kanao

  • 0
    TI__Genius 10370 points
    K.Kanao,

    1) Yes the bq27426 does support reserve capacity. It is located at page 47 of the bq27426 TRM. It is important to note that reserve capacity is only used when Load Mode = 0 meaning the load is modeled as constant current mode.

    2) The gauge will update SOC at routine intervals. Typically this is done at 1Sec, but in sleep mode this is less frequent to save power. The host is able to read SOC and any interval they would like.

    Thanks,
    Eric Vos
  • 0 in reply to Vos
    TI__Intellectual 1710 points

    Hi team


    1 Improve GG accuracy
    Is it possible to imorove accuracy of GG by averaging the SOC result ?
    Do you have any idea to improbe GG accuracy ?


    2. Load mode = 0(current)  or 1(power)
    Would you please let me know the prop and corn for curren load and Power load.
    In TMD Page 44.
    Current mode Prop is descrived as This provides a better estimation of remaining run time,
    especially close to the end of discharge where current increases to compensate
    for decreasing battery voltage.
    What is is Prop of Power mode ?
    How to select current or power ?

    3. Wait time for I2C Standard command
    Is it necessary wait time between I2C Standard command ?
    For EX, after reading Voltage(), then reading State of Health().

    4. Opertaion range  of CC for peak system.
    System current changes 2.3mA to 1A.
    CC counet is delata sigma ADC. CC measumernt would be avereaged during Convertion.
    Do you have any restrict for peak current value and peak time ?
    By the way How much is delta sigma ADC clock ?

    5. GG accuracy
    This GG accuracy is about 5%.
    Customer is  afraind that  Battery cell reaches terminate voltage at SOC= 5%.
    Is this happen ?
    If it is, what is suggeston to avoid it.
    Is one of ides using Reverse cap (set 5% of desing cap) ?

    best regards K.Kanao

  • 0 in reply to Katsuhiro Kanao
    TI__Mastermind 42535 points
    Hi Kanao-san,

    1. No, it really will not improve accuracy. Your last cycle with an avg rate of dsg will be your best bet for the current capacity of the system.
    Accuracy can usually be improved by having a standard dsg at a fixed rate every so many cycles along with relaxation.

    2. Load mode 0 is better. These gauges don't have a simultaneous mesaurement of current and voltage, so in that delta time interval there's an error component in measurement. We suggest use load mode 0 for best results.

    3. We suggest not hammering the gauge continuously and allowing at least 250ms between command sets, meaning if you are reading all the registers, please read all of them once and then allow a 0.25s gap between the next read.

    4. This should be discussed in the DS, please check that.

    5. We allow a best case accuracy of 1% under nominal use conditions. You can set reserve capacity to mitigate for problems where the customer may need graceful shutdown.
  • 0 in reply to Batt
    TI__Intellectual 1710 points

    HI

     

    >Load mode 0 is better. These gauges don't have a simultaneous measurement of current and voltage, so in that delta time interval there's

    >an error component in measurement. We suggest use load mode 0 for best results.

     

    Why bq27426 has a option Load mode =1 as a default ?

    It is better to eliminate Load mode =1, this could prevent customer's confusing.

    Is there any reason to select Load mode =1 and why this is default ?

    best regards K.Kanao

     

  • 0 in reply to Katsuhiro Kanao
    TI__Guru* 76230 points
    A lot of applications are constant power applications hence the need for the load mode to b e set to 1. I don't see it being a source of issues if you load is a constant power load.
    Thanks
    Onyx