• State TI Thinks Resolved
  • Locked Locked
  • Replies 9 replies
  • Answers 5 answers
  • Subscribers 64 subscribers
  • Views 412 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

Li-SOCI2 battery fuel gauge

BQ35100: BQ35100

Dawei
Intellectual 280 points
Part Number: BQ35100

Hi,

BQ35100 is designed to gauge non-rechargeable primary battery, Li-SOCI2 battery is used in my project, after reading datasheet of BQ35100, questions below need your help.

1, What's the temperature stability requirements of sense resistor between SRP & SRN during the overall operating temperature range?

2, In EOS mode, impedance tracking of primary battery is used to predict end-of-service status, so is it still needed to enable BQ35100 when major load pulse current is coming? If it is, the I2C port of BQ35100 should be connected to system controller which knows when major pulse load current come, and BQ35100 can not be configured to operate with a fixed period (24hours) no matter what load current.

3, BQ35100 has internal temperature sensor, is it used in EOS mode default?

Thanks.

Regards,

Ma Dawei

  • 0
    TI__Guru* 76230 points

    Hi Ma

    1. The gauge current ADC is very  stable. You need to make sure to use a sense with better than 75ppm to ensure that there is little drift over temperature.

    2. You need to periodically enable the gauge when your load gets enabled so it measures the changing resistance as the cell is discharged to empty. Your host should have to know when the load is to be enabled to know to enable the gauge before the load gets active.

    3. The gauge can be configured to use the internal temp sensor or the external thermistor. Pls see the technical reference manual on how to do this.

    thanks

    Onyx

  • 0 in reply to Onyx Ahiakwo
    Intellectual 280 points

    Hi Onyx,

    1, Any preferred current sense resistor value recommended or required? 0.1ohm is starting value which is specified in data sheet.

    We have a super cap to smooth our main supply rail, so a bigger current sense resistor maybe needed, is 25ohms OK?

    2, In EOS mode, no reliable remaining battery capacity can be reported by BQ35100, if needed, we ourselves could use measured voltage, current, and temperature to calculate, is it right? By this way, some firmware efforts is needed for us.

    Thanks!

    Regards,

    Ma Dawei

  • 0 in reply to Dawei
    TI__Guru* 76230 points

    Hi MA

    How large is your load current? If it is within a range that the default sense can support, then i suggest sticking with that.

     If your cell is characterised and you get a chem id for it, then the SOC provided by the gauge in EOS mode would be fairly accurate.

    thanks

    Onyx

  • 0 in reply to Onyx Ahiakwo
    Intellectual 280 points

    Onyx,

    1, Our product has two typical load current profiles, one is the measurement activated, about less than 6mA (One super Cap used to smooth main supply rail), the other one is charge circuits enabled, less than 20mA charge current targeted by design (charge current is limited to less than 20mA in order to allow the rechargeable battery to be charged over the overall product operating temperature range, -20 ~ 60C), a secondary rechargeable battery is charged by primary non-rechargeable battery periodically. So at least a several ohms sense resistor will be used? If we want to use 6mA to gauge the primary battery, a bigger than 25ohms sense resistor will be used.

    2, How to characterize our primary battery and get the chem ID? ER34615 (Li-SOCL2) will be used.

    Regards,

    Ma Dawei

  • 0 in reply to Dawei
    TI__Guru* 76230 points

    Hi Ma

    1. 6 mA which is the smaller value is something which the default sense resistor can handle.

    2. The process takes about 6-8 weeks to create a lithium primary id. I have send you a friend request with the details for sending the cell.

    thanks

    Onyx

  • 0 in reply to Onyx Ahiakwo
    Intellectual 280 points

    Onyx,

    For your answer #1 in previous message, I don't follow exactly, do you mean 0.1ohm sense resistor is OK to handle 6mA load current?

    Also, I got your message about the address to delivering our battery samples, thanks.

    Regards,

    Ma Dawei

  • 0 in reply to Dawei
    TI__Mastermind 24870 points

    Hello Ma,

    I would not recommend using a 100 mOhm sense resistor for the bq35100, you are amplifying the noise ratio.

  • 0 in reply to Kang Kang
    Intellectual 280 points

    Hi Kang Kang,

    What's your recommendation for the value of sense resistor of BQ35100 to 6mA load current?

    Regards,

    Ma Dawei

  • 0 in reply to Dawei
    TI__Guru 52115 points

    Hello Dawei,

    Can you try using a 5 mOhm sense resistor?

    I suggest looking at Qpass as well and not the instant current readings. Perform a test where Qpass is at 0, then discharge at 6 mA for 5 hours. Stop the discharge. Qpass should be at 30 mA in this case.

    I believe our EVM uses 10 mOhm sense, you could try that as well.