BQ27320: Settings Gauge

Hello,

Step1) Correct, Battery Capacity stated in datasheet is the nominal capacity and the design Capacity. This parameter shouldn't be changed. It is a copy/paste nominal capacity from cell datasheet.

Step2) For full charge capacity it is a little bit more complex as it requires some charge discharge to determine the true FCC of your battery.

At first you want to keep FCC same as design capacity, but then this value will change after you have collected data (what we call IVT data) during charging and discharging.

G Cant said:

Will I'll be able to export those settings to other chips I have in my Devices or do I have to repeat the process of "learning" with all my Devices at first?

This is correct, you only need to go through the learning process once. Then, you will export what we call the golden image which will contain the configuration file.

Regards,

Jose Couso

Those are great answers, thank you Jose.

I am still doubtful about the "learning process".

Is this process done by the IC automatically? For example, I charge and discharge my battery as usual for a couple of times with the Gauge attached and it should learn it? 

Do I have to enter some "Learning Mode" and configure it first so the Gauge knows that it has to "start learning"?

Will this process also update the other parameters, such as Capacity remaining, minutes until full charge, etc, etc?

Thank you very much.

Hello Cant,

The bq27320 is a CEDV gauge, for these type of gauges there's no much that need to be configured for learning FCC in this case. Once, you have gone through the learning process (which I will guide you), the gauge will report Remaining Capacity, State of Charge, FCC, etc. The gauge does this automatically.

The main parameters that need to be configured before mass production are:
- Design Capacity (user gets the nominal capacity from cell datasheet)
- Terminate Voltage (user gets it from cell datasheet)
- EDV0, EDV1, EDV2. These parameter are called the End-of-Discharge Thresholds. The gauge references to these parameters for best accuracy when near to terminate voltage. The TRM talks about this in section 1.1.4.
     * The gauge offers two configurable options for EDV thresholds:
          1- EDV compensation. This is recommended as the gauge will compensate the End of Discharge based on temperature. For this, you'll use our                  GPCCEDV tool which I will discuss later.
          2- EDV fixed. This method is for when you don't care about temperature. User is responsible to manually calculate the EDV thresholds. This is why              it is recommended the compensated method.
- FCC, for learning purposes user can use Design Capacity. Then update this parameter after learning process is complete. Our GPC tool should output this value, but if it doesn't. Please send me the collected IVT data and I will provide the true FCC value.
- You will also need to configure the the Voltage (0%-100%) DOD table. if the GPC report does not provide this, you can use the collected IVT data in a different tool which will give you the closest chemistry you are using, then I can provide this DOD table for you.

For collecting IVT data for the GPC tool, you will only need to configure:
- Design Capacity
- Terminate Voltage
- EDV0 -> set it equal to Terminate Voltage
- the rest leave it as default.

Please follow the below link for IVT data collection.
https://www.ti.com/lit/ug/sluub45b/sluub45b.pdf?ts=1667489308199&ref_url=https%253A%252F%252Fwww.ti.com%252Ftool%252FGPCCEDV

To configure the DOD table, you will open OCV11 file from the report from the GPCCEDV tool, and copy this table in the data memory parameters. Please see below


Should you have any questions, please reach out.

Regards,
Jose Couso

Hello Jose, I completed the DOD table with values obtained from an external tool. I wrote down the values to the CEDV Profile 1. Is the Gauge configured to check that profile? Should I specifically configure which CEDV Profile look at?

Once I wrote those values I have to do a couple Discharge routines (from fully charged to fully discharged) so the registers update, isn't it?

Right now my "Full Charge Capacity" Register has a value of 1944mAh even though my battery is 3350mAh. Hope that after some discharge routines that value updates by itself...

Thank you for your help.

Hello Cant,

Which external tool did you use to determine the DOD table? This is very important as the gauge uses this value to know the exact voltage of the battery. Can you walk me to what you did?

G Cant said:

Is the Gauge configured to check that profile? Should I specifically configure which CEDV Profile look at?

The gauge responds based on the configurations the user inputs in the data memory parameters. 

If your FCC is much smaller than Design Capacity, chances are that:
1- Cell resistance might be too high
2- Load is very high (1.5 C and above)
3- DOD table is wrong and gauge does not know how discharged the cell is.

Regards,
Jose Couso

I used some approximate values that I've got from experimenting with the battery. I want to make a rough respond not exact, as I am just testing the Gauge. Making the discharge curves with different temperature conditions is a bit overkill for this stage of my development.

The FCC is now within a correct range.

Now that I have the Gauge behaving as I want, how do I export the settings? How can I add the settings to my microcontroller's firmware? Is there an available header file for this Gauge that I can add?

Thank you for your help Jose

I made a mistake with the "Design Capacity", is there a way for resetting this value? Once I reset the value and do another Full Discharge Test, will it update?

Thank you

Hello Cant,

After configuring the gauge, you can export the golden image and upload the golden image file  to your microcontroller. 

Please reference to this app note where it is discussed how to communicate to the the gauge using an MCU. Just remember you are using a ROM gauge when reading the document, there are differences in golden image file format between ROM and Flash gauges.

https://www.ti.com/lit/an/slua801/slua801.pdf?ts=1668094536352&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FBQ27320

As for the design capacity parameter, if you are using the bqStudio GUI, simply navigate to data memory tab and under gas gauging change Design Capacity value. Please ensure the gauge is in unsealed mode.

If using an MCU, you will need to reference to Section 3 Data Flash Interface in TRM.

Also, design capacity does not change. Once you enter the value, the gauge uses it and does not update Design Capacity. This value serves as reference to the gauge to update FCC, RM, SOC, etc.

Regards,
Jose Couso

descarga_load_simm.log

Hello Jose, here is my log for a discharge test I did yesterday. I noticed two problems with the file:

1) The Design Capacity on top of the File is not the Design Capacity I am using in Data Memory (2695 mAh)

2) The log values seems okay but I detected some big jumps in SOC between 1445 and 1446, 3991 and 3992, 4144 and 4145, 4297 and 4298, 4449 and 4450, 4602 and 4603, 4821 and 4822. It goes from a % value to suddenly a lower % value, e.g. from 16% to 0%, or from 58% to 46%.

How can I make the Gauge to not give those big jumps in SOC?

I stablished my DOD values based on another criteria, maybe that is messing with the SOC. Could you give me the real DOD values for my battery based on the log file I gave you? I don't care about a precise respond for the full temperature range, just a close-to-precise in my ambient temperature.

Thank you for your help. 

Please take into account that the first 40 values are mistaken, you can see that the voltage starts lower than the voltage at row 40. 4.1V is my 100% threshold, and 3.3V is my 0% threshold.

Hello Cant,

1- Chances are that even though you entered a new Design Capacity, it wasn't written in data memory of the gauge. This could be due to not unsealing the gauge first. To double check you have the right Design Capacity value, please read back the value.

Also, check below



2- The DOD table plays a big role here along with EDV2, EDV1, and EDV0. In your log file I see Remaining Capacity not smooth as EDV is reaching.

Please attach your configuration gg file to further investigate this scenario. 

G Cant said:

How can I make the Gauge to not give those big jumps in SOC?

I can't say for certain, but most likely it's the DOD table along with EDV2,1,0. I have to check your configuration.

G Cant said:

I stablished my DOD values based on another criteria, maybe that is messing with the SOC. Could you give me the real DOD values for my battery based on the log file I gave you? I don't care about a precise respond for the full temperature range, just a close-to-precise in my ambient temperature.

If temperature is not a concern, then I suggest you configure the EDV threshold with the fixed method. 

I can provide a DOD table if I know the Chemistry ID you are using, and I can match it to one in our database. For this, what is typically done is the user collects Current, Voltage, Temperature - IVT data, and uses our GPCCHEM tool. This tool will give you the most close matching Chemical ID to your cell. With this information, I can provide a DOD table for you. 

Please see below our GPCCHEM tool link. There's a simple guide for this as well.
https://www.ti.com/tool/GPCCHEM

https://www.ti.com/lit/an/slva725a/slva725a.pdf?ts=1668184512812&ref_url=https%253A%252F%252Fwww.ti.com%252Ftool%252FGPCCHEM


Regards,
Jose Couso