• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 64 subscribers
  • Views 535 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

BQ33100 capacitance measurement

lu chenghu
Prodigy 20 points
Other Parts Discussed in Thread: BQ33100

To anyone who may concern,

I am using BQ33100 for capacitance measurement. I found the results were different from time to time on the same capacitor.

If I send learn command to BQ33100 immediately after power on, I found the capcitor would charge and stabilize to a certain point which the charging current was no more than 40mA and it would start learning there. The result learned in this way is always smaller than the result learned when the charging current is less than 10mA after a long period of charge.

The capacitor measured is 10F in theory, if I charge it quite a long time then send learn command, the result is 8.8F; but if I send learn command immediately after power on, it is about 8.5F.

Any suggests on how to make it more accurate?

Besides, is there any source code in C available for evaluation?

        Regards

Lu

  • 0
    TI__Guru* 76230 points

    it is preferable to start learning close to what your Vnominal is and not immediately after power on. You can reduce your learn load current, for improved capacitance measurement but the trade off will be in the ESR measurement. ESR measurement is improved with a stronger load.

    -Onyx

  • 0 in reply to Onyx Ahiakwo
    Prodigy 20 points

    Thank you for your valuable answer,

    As you mentioned that learn load current plays a big role in capacitance and ESR measurement.

    Here are my questions,

    1, How can I adjust learn load current, do you mean change the value of R27, R28 (page 50 of bq33100 spec)?

    2, I used Nesscap ESHSR-0010C0-002R7 in my design, its nominal capacitance is 10F, rated voltage is 2.7V. We made a capacitor array with 9 of them (3X3, serialized 3 group of paralleled capacitors with 3 ones for each group), each single capacitor in the array works at 2.4V. From the capacitance distribution chart provided by our supplier, a single capacitor is expected to be 10.2F; but the value we measured by TI EVM was 8.91F, we also build a board using the bq33100 solution, our board returned the same result.

    Here is the super capacitor’s supplier's test method,

    The capacitance is calculated from discharge using 100mA, from 80% rated voltage to 40%, after 5 min of voltage clamp at rated voltage. 

    So, why it is 8.91F measured by bq33100 since it is expected to be 10.2F?