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BQ4050: Updating MaxError and FCC

Laurence Symonds
Intellectual 545 points
Part Number: BQ4050
Other Parts Discussed in Thread: GPCCEDV, BQ25703A, BQSTUDIO

Hi

I have run the GPC cycle and am trying to update the FCC. I charge the device up until VCT is high. I then discharge the batteries until max. I am using 18650 cells that have an internal protection circuit that cuts out at 2.8V. I am discharging the batteries down until they cut out. This is causing the device to reset. Am I right in thinking for the MaxError to update, I need to stop the discharge before the protection circuit cuts out?

Also, I ran the GPC cycle discharging from about 4.15V per cell. For the device, we want to extend the battery life, so want to charge to 4.1V and discharge to 3.3V. I want the SoC to go from 0% to 100% between those cell voltages.

Can I run a discharge to update the FCC, then enter that value into the Design capacity? I will also update the charging voltage values for all temperatures in advanced gauging algorithm. Are there any other registers I need to set to adjust SoC limits?

Thanks

  • 0
    TI__Guru 52115 points

    I will take a look tomorrow and then get back to you.

  • 0 in reply to Andy Liu (BMS)
    Intellectual 545 points

    Hi

    Sorry but I have some more questions.

    I've noticed that I am running into the protection limits at the extent of charging and discharging and this may be effecting the FCC learning.

    When I discharge the battery down, without manually stopping the discharge myself I have noticed that if I reach the CUV condition, I get an XDCHG event but then also the EVM I am using will stop responding. I am guessing this is causing either a reset or is cutting power somehow. I looked at the schematic and VCC of BQ4050 is connected the battery side of the DCHG FET, so even if it gets switched off, the BQ4050 should still get power right? This unresponsiveness happens at whatever voltage I set the CUV at. If I set it high at 3.5V, it still causes the BQ4050 to go offline. I can get it back by providing a charging current. Is this an expected condition?

    Secondly, what is the recommended value for overcharge (OC) threshold? The default is set to 300mAh. The FCC I currently have is 1992mAh, which is less than then actual capacity and as mentioned before, it is not updating. Because of this, I enter the OC condition well under the full charging voltage. I am just wondering, should I be setting the OC threshold to around my design capacity, so it is a protection that is further down the protections priority list or should it stay low so that if RemainingCapacity > FullyChargedCapacity, it will always get triggered?

    Thirdly, If I am in the OC condition and I send a reset, The RemainingCapacity drops right down. As I understand it, the RM is calculated based on the coulomb counter, but on reset, how is this value calculated then?

    Thanks

  • 0 in reply to Laurence Symonds
    TI__Genius 10370 points

    Laurence,

    If you are discharging the device until it is powering off then you will be unable to successfully learn. This will cause the gauge to reset and learning will be canceled. 

    bq4050 is a CEDV gauge. You need to collect 6 log file (3 temps, 2 Dsg rates) and feed them into our CEDV parameter calculator online. Once you have the updated parameters a learning is as simple as a single discharge from full to empty. You will specify the termination voltage you want in the upload

    http://www.ti.com/tool/GPCCEDV 

    OC threshold is very application specific. This is a value you want to protect your end device from. We cannot really recommend a value here. 

    Thanks,

    Eric Vos

  • 0 in reply to Vos
    Intellectual 545 points

    Hi Eric

    Thanks for the response.

    So for the termination voltage that is in the config.txt file submitted with the GPCCEDV calculator, I used the value of 2800, which is the voltage that the internal protection circuit in the 18650's will disconnect at. I want to discharge the batteries so a discharge to 0% is roughly 3300mV in the rested state. Should i resubmit my log files with 3300mV as the termination voltage? All the log files log readings going below 3300mV, but will the calculator ignore these values after the termination voltage?

    As for the OC value, could you at least give me some pointers as to which factors are important when trying to correctly set the threshold value? When you say it is application specific, could you give some example applications where one value or another would be chosen? Not sure if it's relevant, but the charger I am using is the BQ25703A. I guess I will set the OC threshold to the design capacity for now and see how it works out.

    Thanks

  • 0 in reply to Laurence Symonds
    TI__Genius 10370 points

    Laurence,

    Yes you should re-submit with 3.3V. From there the tool will calculate the correct gauge settings to report 0% at 3.3V. 

    For the protection are you asking about OC (Over Charge) or OCC (Over Charge Current). I was referencing OCC which is a Max value your PCB/Batteries can handle. If you are asking about OC, this value should be left default (300mA) This is an amount of charge you need to apply AFTER Remcap=FCC. Setting this equal to designcapacity means you will need to pump in 2X the true capacity before the protection will trip. Once the gauge is setup correctly a value of 10%-20% should be good. 

    Thanks,

    Eric Vos 

  • 0 in reply to Vos
    Intellectual 545 points

    Hi Eric

    Thanks for the reply.

    I will try out the new EDV values with 3.3 termV and let you know.

    I was previously referring to OC, not OCC. From the TRM, I understand the description to mean that when both remcap>=FCC and charge counter >=OC conditions are true, it will trip. I didn't realised it was when remcap>=FCC+OC it will trip.

    On my EVM device, with BQStudio, the OC trip flag was being raised, but the FCC isn't getting set properly, so that could be the issue.

    Thanks