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BQ27750EVM-837: Configuration/ Steps for beginners

Eugene Grobbelaar
Prodigy 135 points
Part Number: BQ27750EVM-837
Other Parts Discussed in Thread: BQSTUDIO

Hi Guys

I have gone through the following excellent topic thoroughly "https://training.ti.com/gauge-programming-fundamentals"

Unfortunately the gauge parameters required for configuring there are slightly different. Nevertheless...

I have attached my battery to the EVM, fired up bqStudio and configured the following (under Data Memory -> Gas Gauging):

(*) - Design - Design Capacity mAh (850 mAh)

(*) - Design - Design Voltage (3700 mV)

 - FC - Set Voltage Threshold (4200 mV -> my battery requires this as the CV voltage for charging)

 - FC - Clear Voltage Threshold (4100 mV -> following suite of the default parameters)

- State - Qmax Cell 1 (850 mHh -> even though I change design capacity, this still keeps default of 5359 mAh, which would logically appear to be wrong IMHO)

- State - Qmax Pack (same as Cell 1)

(*) - IT Cfg - Term Voltage (2800 mV -> I guess this should maybe be a bit higher than the manufacture specs, as at that point of discharge one starts to damage the battery, but so far no discharge)

Question 1 :

What are the the minimum parameters that need to be changed to make it work for my system? (*) denotes the parameters that I can find that match those mentioned in your guide in the link, but the others I can not find (i.e. 'Taper Voltage' and 'Taper Rate')

Question 2 :

Based on my configuration, bqStudio says that my battery is at 25% SOC. I am assuming that this is because it has already charged my battery to max capacity with the incorrect parameters first, and now that it may have the correct capacity, it has incorrect book-keeping...so how do I restart this? Do I need to discharge the battery?

Question 3 :

The device I am working on will be a compact device, and will house the battery inside (non-removable), with the bq27750 on a PCB connected via I2C to a microcontroller. As such, I dont beleive it will be possible to use the bqStudio 'Golden Image' for pre-production configuration...is my beleif correct? Is it standard practive for devices to program the gauge upon start up first time, with battery connected, if parameters are not right?

Thanks for your time.

Regards,

Eugene

  • 0
    TI__Genius 10370 points
    Eugene,

    Thanks for Reaching out so that we can assist you. let me answer your direct questions first.

    Q1: Here is a list of the minimum parameters recommended to be changed.
    1) Calibration. Our gauge rely's on accurate voltage and current measurements so it is very important calibration is done on the device. it is more
    important on your system board as the EVM calibration should be close by default but still recommended.
    2) Protections/Permanent Fail. It is imported to set the thresholds and recovery's correctly so that your testing and learning in not interrupted. COV
    and CUV are the big ones. For COV we recommend 50mV greater than your CV point of the cell.
    3) Advanced Charge Algorithm. This is where you will find "Taper Rate" = "Charge Term Taper Current" and "Taper Voltage" = "Charge Term
    Voltage" . This is what the gauge will think is fully charged. you need to set the Voltage parameters under the [Low, Standard, High, and Rec]
    sections to be the correct CV point. when you battery voltage gets within Charge term Voltage of charging voltage it will start looking for your
    current to be less than "Taper current"
    4) Gas Gauging. This is the guts of the gauge and starting off we want the gauge to think it is already as close to the real application as possible. to do
    so please set the following.
    Design Capacity mAh = 850
    Design Capacity mWh = 314
    Design Voltage = 3700
    Terminate Voltage = Where you want your system to think it is 0% normally this value is 3000mV for most Li-ion cells
    Qmax Cell 1 = 850 *this need to be update since it is not pulled from Design capacity. it isnt pulled because over the life of the cell as it ages
    this parameter will change
    QMax Pack = 850 * Should be the same as Qmax cell 1. This parameter is normally used for mutlicell applications
    Cell 1 Chg Voltage at EOC = Set this slightly below (10mV) your CV mark. 4190mV
    5) Chemistry: The gauge will work and function without updating this but for the best accuracy a correct chem ID is needed. you can use the
    chemistry plug-in to search for your cell or you can run cycles on your own to find a match. for more info on this let me know

    Q2: Once you have set all the above parameters correctly and you battery supply voltage is stable; stable being the cell is rested or a power supply is used. All you need to do is issue a reset command (0xAA, 0x00, 0x0041). once the device is running resets are not recommend to be used since our gauge learns certain things in RAM while running, but for initial setup it is good to get a good starting point.

    Q3: There are a few normal flows for production. since this product is designed to be a pack side gauge normally it is programmed outside the system then the pack is inserted into the system. it is possible to use your host micro to do the programming . info can be found here training.ti.com/gauge-programming-fundamentals

    Not all of this is needed to get a basic test is the gauge working, but i feel it is worth the time to setup. If you would like to have a short call and we can do a working session please let me know and we can get one setup

    thanks,
    Eric Vos
  • 0 in reply to Vos
    Prodigy 135 points

    Hello Eric

    Many thanks for your detailed reply.

    Before I received your reply, I was trying to download a 'golden device image' from bqStudio (I heard, in the 'programming fundamentals' that one of those files has all the commands necessary to reinstate flash memory). Part-way through, bqStudio crashed, and was never able to recognise my EVM again.

    I have since then gotten a freshly installed laptop (thats also quite new) and reinstalled bqStudio as well as the EVM drivers.

    But still it can not recognise my EVM.

    There is no 'unknown device' in the windows Device Manager.

    Until I can get this working, I can't go through your details.

    Best regards,

    Eugene

  • 0 in reply to Eugene Grobbelaar
    TI__Genius 10370 points

    Eugene,

    I am sorry to hear about that. Can you give more detail about which screen and procedure you followed when it crashed? Unfortunately if it crashed when the device was in ROM mode exporting a golden image it could have corrupted something. Let me work with you offline to see if we can recover it.

    Thanks,

    Eric Vos

  • 0 in reply to Vos
    TI__Mastermind 25955 points
    Hi Eugene,

    Quite some time has passed - If your issue still isn't resolved, please provide the information requested by Eric above.

    Sincerely,
    Bryan Kahler
  • 0 in reply to Vos
    Prodigy 135 points
    Thanks for the fantastic support Eric.