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Original question:

BQ34Z100-G1: What DataFlash parameters affect state estimation at power-up/chip reset?

BQ34Z100-G1: Which DataFlash parameters control when SoC gets re-measured based on OCV (etc.)?

Kevin Banks
Prodigy 235 points
Part Number: BQ34Z100-G1
Other Parts Discussed in Thread: BQ34Z100

In other words, which parameters control when the chip STOPS updating SoC based solely on coulomb counting and instead updates it based on other measurements?

Example - over the course of a charging cycle the battery reaches the fully charged voltage level, but the SoC only makes it up to 72%.

If I reset the chip, it changes it's SoC estimate to 100%.

Which DF parameters would cause that sort of "reassessment" to take place automatically/without having to restart the chip?

Note - I have been readings the docs regarding parameters like "taper current" but they are unclear.

Perhaps someone can point me to a document focusing on Taper Current, Current Taper Window, Cell Taper Voltage, etc.

  • 0
    TI__Genius 10370 points

    Kevin,

    In the example you gave the "Reset" is causing the gauge to do a voltage lookup and establish the SOC based on voltage only. This is not ideal because your voltage is inflated due to the charge current which will report an overly high SOC. 

    If the gauge is only reaching 72% when you charge you need to a make sure the gauge is getting a VCT(valid charge termination event). At a VCT event the gauge learns this point as the new "Full Charged" point and the capacity simulation is run from there. Then on the next cycle you should reach 100% at the correct time. 

    Thanks,

    Eric Vos

  • 0 in reply to Vos
    Prodigy 235 points

    I don't think the voltage is inflated at reset due to charging current (the charger is off in the scenario I am describing).

    I think the 100% determined there is correct.

    I do think you are on the right track with your comment regarding VCT Events. My original question could probably be rephrased "What DataFlash settings control generation of VCT events?"

    This might clarify the scenario some more - the actual charging is under the control of a TI BQ24650RVAR Battery Charger chip.

    We are just having trouble getting the BQ34Z100 to "follow along".

    1. What DataFlash settings control generation of VCT events?

    2. When a VCT Event is generated, and a new capacity simulation is run, why doesn't the SoC update then? (Why does it not just up to 100% then?)

  • 0 in reply to Kevin Banks
    TI__Genius 10370 points

    Kevin,

    The section you will want to get to is on page 30 of the technical reference manual. 

    https://www.ti.com/lit/ug/sluubw5/sluubw5.pdf?ts=1621287335099&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FBQ34Z100-G1 

    When a VCT event does occur SOC is jumped to 100%, this is one of the rules. Since you dont see 100% it makes me believe you have not gotten this VCT.

    Let me know if you are not able to find the right information. 

    Thanks,

    Eric Vos

  • 0 in reply to Vos
    Prodigy 235 points

    I do see section 3.7 in the TRM, and in my original post I said that this was unclear to me, and that I was looking for any other documentation on the same topic.

    Can you point me towards a worked-out example, or an application note, or a different manual?

    When section 3.7 - A - 2 says "accumulated change in capacity > 0.25 mAh" do they mean "since charging began"? Or during "two consecutive periods of Current Taper Window"?

    When the first sentence in section 3.7 references "Cell Charging Voltage", do they mean these three fields?

    Configuration,Data,Cell Charge Voltage T1-T2,3600,mV
    Configuration,Data,Cell Charge Voltage T2-T3,3600,mV
    Configuration,Data,Cell Charge Voltage T3-T4,3600,mV

    Or do they mean this field?

    "Configuration","Charge Termination","Cell Taper Voltage","100","mVolt"

    You also said "When a VCT event does occur SOC is jumped to 100%, this is one of the rules."

    Is this regardless of the setting of the RMFCC bit?

  • 0 in reply to Kevin Banks
    TI__Genius 10370 points

    Kevin,

    That is the best description. I can address your questions though

    1) the 0.25mAh is over the single 40sec window. it is just to make sure you have actual charge current flowing and not at 0. this is not satfsified if you tape WAY down to like 5mA/10mA

    2) Your voltage needs to be within [Cell taper Voltage]*NUMCells of [Cell Charge Voltage]*NUMCells to start looking for VCT. Yes the voltages you note are the correct ones. although the ones you list are very small. i expect these values to be 4.1V-4.4V unless you are using a different chemistry. if you are using NMH cells the charge taper is 100% different. 

    3) RMFCC needs to be set, i assumed it was since i dont know of a valid case to have this cleared

    If you are not getting VCT most likely your voltage is not coming within the range

    Thanks,

    Eric Vos

  • 0 in reply to Vos
    Prodigy 235 points

    So for example if I have charging voltage and/or taper voltage set too low, by the time we get to that point in the charging cycle the current may be too low to meet the 0.25mAh requirement, thus preventing VCT detection?

    As for RMFCC, I "inherited" this golden image file and don't know why the previous engineer did not have this bit set. I did try a test yesterday with setting this bit, and this change ALONE was not enough to detect the end of the charging cycle (SoC did NOT jump up to 100%). However, I think with your other comments we are on the right path to correcting this.

    For "accumulated change in capacity > 0.25 mAh per CurrentTaperWindow", is that 0.25 mAh value fixed, or is it configurable?

    If it is configurable, is this what the MinTaperCapacity field is for?