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BQ33100: Questions for Capacitance Learning feature

Randy Chen
Intellectual 2295 points
Part Number: BQ33100

Hi,

Customer is testing BQ33100 and got below questions.

1. As described in the section 8.3.1.1 of the datasheet. For the learning process 1 and 3, is it charge to full? Is the discharge time fixed for the learning process 2 and 4? If the discharge time is not fixed, how BQ33100 determined discharge done?

2. After we gave the Learn command and wait for around 1 minute, we can see the supercap started the discharge for 6 seconds and stop and wait 1 more minute and discharge another 1 second then showed "Learn completed successfully" and the supercap status messages. See below captured pictures. Does it mean complete a learn cycle?

3. In the failed board, we can see the first time supercap discharge spent more than 20 seconds and then keep in Learn in progress till relearn timed out. We would like to know what kind of error may caused it been hold in Learn in progress and failed to complete the Learn cycle? 

Best regards,

Randy Chen

  • 0
    TI__Mastermind 25955 points
    Hi Randy,

    To determine what caused the learning cycle failure, a more complete log showing current, stack voltage, and other device parameters.

    For example, monitor [CL] and [LPASS] to determine when a qualified capacitance learning cycle begins. [LPASS] in Operation Status will set when a qualified learn has occurred.

    During the learning process there are specific timeouts to protect from over charge or over discharge of the super capacitor array. At the beginning of each phase of charge and discharge a timer is started. If the timer exceeds Max Discharge Time during the discharging phase then Operation Status [LDTO] is set if the timer exceeds Max Charge Time for the charging phase then Operation Status [LCTO] is set. the flags are cleared upon the beginning of the next learning cycle.

    Please check to see if [LDTO] is asserted at the end of the cycle, this would indicate that the Max Discharge Time was exceeded. Similarly, check assertion of [LCTO] to determine if Max Charge Time was exceeded.

    If time is exceeded, the learning load may not be sized for your application. To learn more about sizing the learning load, please refer to section 7 of this app note: www.ti.com/.../slua751.pdf

    Sincerely,
    Bryan Kahler
  • 0 in reply to Bryan Kahler
    Prodigy 60 points

    Hi Bryan

    About this question, I think root cause is supercap discharge rate too slow ,
    because failed board's Q8 Rds(on) is too high and affecting the discharge rate.

    I use oscilloscope to observe "learn process" ,when the bq33100's LLEN is high will start to discharge ,
    ‘’pass board’’ just use 6s but ‘’failed board’’ use over then 25s ,so causing timed out.
    After continuous timed out alilog will show "Battery has failed and cannot support date retention lease replace the battery".
    So I would like to know ,when learn process start to discharge(step2) ,what discharged level (80%, 60%, 40% or 20%) does it require during step2, so it can move on to next step?

  • 0 in reply to user5793901
    TI__Mastermind 25955 points

    Hi Randy,

    Please make sure the learning load allows for a measurement of at least one second.  Learning current should be high enough to provide at least a 25 mV drop.  A larger drop will result in more accuracy.  An excerpt from the recommended solution above:

    Sincerely,

    Bryan Kahler

  • 0 in reply to Bryan Kahler
    Prodigy 60 points

    Hi Bryan

    1.When learn process start to discharge, supercap volt will from 13.6V to 10.4V, volt drop is more than 25mV, why is it still not finished discharge(step2) and move on next step?

    2. I would like to know, if follow bq33100’s SPEC design, and use 6.5 F supercap, how much learning load do we need? 100 mΩ ESR is mean ESR of discharge path? Ideal learning load is mean discharge current?

    thanks

    Iven

  • 0 in reply to user5793901
    TI__Mastermind 25955 points
    Hi Iven,

    1. Please ensure that the values in data flash are properly set with respect to section 8.3.1.4 Qualified Capacitance Learning of the datasheet. For example, LEarning Config> Learning Frequency, Measurement Margin %, Max Chg Time, Max Dsg Time, Learn Delta Voltage, Cap Start Time. A log file monitoring all flags of the device would be helpful here. A learn cycle may fail if the device is under load or the load changes during the learn cycle.

    2. Please use the formula above to determine the drop required for your application. Please make sure the learning load drop occurs over a time period greater than 1 second and voltage drop in excess of 25 mV.

    Sincerely,
    Bryan Kahler