BQ27Z746: Query on learning cycle and chemical ID identification of LiPo battery

Hi Adrian,

We successfully calibrated the fuel gauge at a battery voltage of 3623 mV. However, when we attempted to update the OVP and UVP values to 4100 mV and 3300 mV, respectively, an autotrim failure occurred for the OVP. Currently, the charging toggles every second during the recovery time.

Could you please help us resolve this issue as soon as possible? We are in a critical situation, as the board needs to be delivered to the customer within four days following this learning cycle process.

Hi Adrian,

Please let me know what is meant by the Applied pack voltage specified in the calibration field?

Hi Adrian,

We have completed the process for the chemical ID and have received the log file. However, the GPC tool is continuously sending error messages while uploading the extracted file. Kindly verify the attached files and provide us with feedback.

3443.GPC_ChemID_Data.zip

Hello Gopika,

This is what the voltage and current graph First, there should be a constant current discharge, as you can see the current slowly start to increase as the discharge goes on. Also, at the end of discharge there is just weird charge pulse that occurs that should not happen.

Regards,

Adrian

Hi Adrian,

We have received the chemical ID 2589. However, this ID is not available in the battery chemistry options for programming via "Program Selected Chemistry." Therefore, we plan to program the chemical ID using the GPCRB file.

Could you please clarify what this file is and where I can obtain it? I’ve attached the files we received after submitting the log file from the REL-DIS-REL process for your reference.

Additionally, could you specify whether the battery needs to be fully charged at the initial state of the learning cycle, specifically during the initial discharging cycle?

We also attempted to change the update status to 00 by enabling the gauge and resetting it via toggling. Unfortunately, the update status is currently showing 01. Could you provide guidance on this as well?

Chemid-2-report.zip

Hello Gopika,

I can see the ChemID 2589 on my side. Make sure you update the chemistry version for BQStudio. https://www.ti.com/tool/GASGAUGECHEM-SW

The battery can be in any state for the initial discharge, does not need to be fully charged.

What command did you use to enable the gauge?

Regards,

Adrian

Hi Adrian,

We programmed the ChemID using 'Check for a newer chemistry update on ti.com' and now its fine. We toggled the 'GAUGE_EN ' in the 'Commands' bar (On the right side of BQStudio ) and enabled the GAUGE_EN bit in the Manufacturing status register, but the Update status 01.Please help us to resolve this at soon as possible because we need to complete the learning cycle on high priority.

Best Regards,

Nithya

Hello Nithya,

Can you send me a log file from the gauge of you sending the "GAUGE_EN" command. Can you also send me the gg file from the gauge before and after sending the "GAUGE_EN" command.

Regards,

Adrian

Hi Adrian,

Attached is the log file showing the start of the learning cycle process. The log begins with the 'GAUGE_EN' command, followed by a complete battery discharge to empty, a 14-hour and 36-minute relaxation period, and charging the battery to 4.17V(Dis-Relax-Charge).We will send the gg files as soon as possible.

log file.zip

Hi Adrian,

Please find the attached .gg file showing the gauge status before and after executing the 'GAUGE_EN' command. We tried multiple times to update the 'update status' in Gas gauging according to the guidelines outlined in the Achieving the Successful Learning Cycle document, but it didn't work properly as expected .

We would appreciate your prompt assistance in resolving this issue, as this task is a high priority for us.

We are also attaching a document detailing the procedure we followed for identifying the ChemID and completing the learning cycle . Kindly review it and help us to resolve the issue.

gg_file_and_process_flow_doc.zip

Best regards,

Nithya

Hello Nithya,

I see what happened now, for some reason bit 0 of the update status register was already set to begin the test. I would recommend restarting the learning cycle process. Before you restart, make sure to change bit 0 back to 0 (green). Update status can be found in the gas gauging section of data memory.

Regards,

Adrian

Hi Adrian,

We attempted to update the 'update status' bit by toggling bit 0, and it is now in a low state. Following this, we restarted the learning cycle process. However, after completing the full charge and entering the relaxation phase, the QMAX bit in the IT status is not updating to high as expected.

At this point:

• VOK and RDIS are both in low state.
• REST bit is in  high state.

We have attached the log file for your reference. Please assist us in resolving this issue.

4111.log_file.zip

Hi Adrian,

We have completed the learning cycle as outlined in the documents "Achieving The Successful Learning Cycle" and "Simple Guide to Chemical ID Selection Tool (GPC)" from TI. This process took three days to finalize.

Initially, we conducted the chemical ID test. Subsequently, the gauge was programmed with the obtained chemical ID 2589, and we completed the learning cycle. The steps involved in this process are detailed in the attached document, along with notes on results that did not meet our expectations.

Could you please advise on how we can ensure the accuracy of the golden image obtained from this process? PFA the srec file with this reply.

ChemID_and_Learning_Cycle_Procedure_for_BQ27Z746_REVB_14OCT2024.pdf

ChemID_Data.zip

Hello Gopika and Nithya,

I looked over the log file and see something very concerning.

As you can see, the voltage rapidly jumps about 300 mV without a change in current. This is mostly the cause of why the learning cycle is failing to complete. Battery voltage should not be jumping like this

Regards,

Adrian

Hi Adrian ,

The charging process completed without any physical disturbances in the surroundings, but we will check this . If possible, could you suggest why this behavior might be occurring?

Regarding the learning cycle, we reconfigured some threshold values (e.g., UVP, OVP) in the golden image obtained from the previous learning cycle. We need a new golden image. Could you please confirm whether we need to restart the learning cycle with the new configuration, or if it’s sufficient to take the new golden image directly from the 'Golden image' menu after reconfiguration?

Regards,

Nithya

Hi Adrian,

We used the fuel gauge BQ27Z746YAHR and performed learning cycle again to generate the golden image. But during the process we didn't get some of the bits  correctly as mentioned in the reference document of TI for performing learning cycle. 

Initially we set the Update status to "00" and after toggling the GAUGE_EN command in BQ-Studio the Update Status changed to "04".

After that we started discharging and completed the next relaxation, including initial charging. Until this the bits are changed as per the expectation.

But during the relaxation after charging, the Update Status didn't changed to "05" and QMAX bit didn't toggled to indicate QMAX update. 

In order to proceed further, we manually edited the Update status to "05". Then continued with discharging of the fully charged battery(4.1V Lipo battery).

After completing the discharging we started the relaxation state. But the REST bit didn't get high even after we waited for more than 10 Hours. The update status was supposed to be "06" or "0E" by this time. As this doesn't happened, we manually wrote the Update Status to "06" and waited few hours to check whether will it be get automatically updated to "0E". But this also didn't worked. So, we performed one more Charge-Relaxation-Discharge cycle as mentioned in the reference document. But that also didn't give any expected results.

So after keeping the battery in 1 hour relaxation we manually edited the Update status to "0E". We kept the battery in that state for half an hour and completed the learning cycle by generating the Golden Image.

Could you please help us to identify why we didn't get the proper bit updates in BQ-Studio and to find out if there are any errors happened during the process?

Please note that the discharging is started at 300mA load current for fully charged battery. Later this load current is reduced to 20mA at 3.2V as the battery should be discharged to the termination voltage (3140mV) and the low battery voltage was not able to drive higher load. Do the above mentioned method is correct for discharging or can you please let us know which is the correct method for discharging?

Please find the attached Log file generated during the entire learning cycle and gg file generated after completing the learning cycle for reference

The Chem ID used in the process is : 3759

Battery Details : 3.7V, 1500mAh, Li-Po Battery

The reference document used is : SLU903 ( Achieving the Successful Learning Cycle ) by TI.

0333.FUEL_GAUGE_LEARNING_CYCLE_01NOV2024.gg.csv

0333.LOG_FILE.zip

Hello Gopika,

Thank you for the data, give me some time to look through the data and root cause your issue.

Regards,

Adrian

Hello Gopika,

Please do not manually change the update status register, this should update automatically. I will need you to manually change update status back to 0x04. Can you reattempt the learning cycling but this time discharge all the way down to 2.5V and make sure to relax for 5 hours. Then charge to all the way up to 4.2V.

Regards,

Adrian

Hello Adrain,

We waited hours to change the update status automatically. Unfortunately this doesn't happened. Currently we have discharged the battery to 3140mV. Now  as per your suggestion we need to discharge the battery to 2.5V so we have to remove the BMS protections. But as per the datasheet of LiPo battery used the discharge cut off voltage is 2.75V. Can this been done? Please comment. Hereby attaching the datasheet of battery with this.

7215.SDS 503450.pdf

Hello Gopika,

Yes, only discharge down to 2.75V.

Regards,

Adrian

Hi Adrian,

We have some queries regarding the updating of data memory related to the 'term voltage' which is explained below . Could you please provide clarification on this, 

1. If set the term voltage to 2750mV as suggested , there are chances that the battery voltage will directly drop to 0V before reaching to the term voltage and the fuel gauge will not detect the battery after that for further steps. Because in earlier ,when we fully discharged  the battery individually with an electonic load having constant load current of 300mA ,  observed that battery voltage dropped to 0V when reaching 2.953V at battery voltage ,but the expected cut-off voltage was 2.75V according to the discharging rate mentioned in the data sheet.
2. If  reducing the discharging current after the battery voltage reaches 3.3V and expected that the the cut-off of the battery might occur slightly below 2.953V.
So can we proceeds to update the data memory using the below values? is it okay to set the Term voltage as 2.9V?

Termination voltage : 2900mV
CUV : 2850mV
UVP : 2870mV
UVP Recovery : 2880mV
CUV Recovery : 2860mV
FD Set threshold : 2910mV

Please help us to provide clarity on this.

Regards,

Nithya

Hello Nithya,

This should hopefully be fine. We will see if this allows the update status to change to 0x05. Please start another learning cycle attempt with these settings.

Regards,

Adrian

Hi Adrian ,

Thank you! We'll perform the learning cycle and update you with the results as soon as possible.

Regards

Nithya

Sounds good, I will be awaiting to hear from you.

Regards,

Adrian

Hi Adrian,

We began the learning cycle by updating the data memory values as previously discussed, setting the term voltage to 2900mV. Initial discharging began with a constant load current of 300mA. At around 3.2V, we reduced the load current to 150mA and continued discharging. When BQStudio detected a voltage of 2953mV, the battery voltage drained to 0V. so we were unable to drain the battery voltage down to the term voltage.

Can we able to decrease the load current below 150mA for discharging ? or need to use constant discharging current during entire process?

In the reference document, it is stated that the final discharging current can be as low as C/10 but in the initial discharging not specified about load current. For our battery, C is 1500 mAh. However, in terms of new term voltage value, we cannot discharge to meet the term voltage because this would drain the battery to 0V.

Please specify about the discharging load current in detail way in both initial and final discharging steps

Please provide clarity on this ,your support on this would be appreciated.

Regards,

Nithya

Hello Nithya,

You will need to use a constant current when discharging. I would recommend using a rate of C/7 and don't step down this current. Discharge down close to the point where any protections will trip.

Regards,

Adrian

Hi Adrian,

Good news ! 

Thankyou for your support.

We reattempted the learning cycle with a constant load current of 150 mA during discharge . Currently, the process is progressing as expected, with the update status bit now showing 05. Currently second discharging is ongoing.

However, we have a concern regarding the golden image exporting  process. In the reference document, we noticed a sentence in the conclusion page which shown below, we need to do this before exporting the golden image file? Please provide clarity on this.

Hello,

The team is currently out of office today. We will get back to you next week.

Regards,

BMS Apps Team

Hi Adrian,

Thank you for the information. 

We have a Good news, and thank you for your continued support!  

During the final relaxation stage of the learning cycle, we observed the Update Status bit transition from 05 to 06. However, it did not change from 06 to 0E in the final relaxation.  

As per the reference document, we are now performing another Charge-Relaxation-Discharge cycle. During the relaxation phase after charging, we were able to observe the Update Status change from 06 to 0E. The remaining discharging cycle still needs to be completed.

That said, we have a few concerns regarding the next steps in the learning cycle, and we would appreciate your guidance on the following:

• Is it acceptable to take the golden image during the relaxation phase after charging (since the Update Status is 0E), or should we complete the discharging phase, as mentioned in the reference document, before capturing the golden image?  

• If discharging is necessary, can we take the golden image immediately after the discharging phase, or should we wait for the REST bit to go HIGH to ensure proper relaxation?  

• The reference document states that before saving the golden image, we must set the Update Status to 02 to disable IT gauging, reset the Qmax Cycle Count to 0, and set the Cycle Count to 0. Is this step required, or can we proceed with taking the golden image once the Update Status is 0E?  

We would greatly appreciate your insights and suggestions on these points.  

Regards,

Devika 

Hi Adrian,

Thank you for the information.

As discussed, since we have not observed the transition of the Update Status from 06 to 0E, we conducted another Charging - Relaxation - Discharge cycle as described in the reference document. Due to uncertainty about when to generate the golden image, we created three different golden image files throughout the process after getting the Update status to 0E , as outlined below:

1. The first golden image was generated when the Update Status changed to 0E during the relaxation phase after charging, without altering the Update Status, QMAX Cycle Count, or Cycle Count. At that time, the values were 0E, 2, and 2, respectively.

2. The second golden image was generated after completing the final discharge in the Charge - Relaxation - Discharge process, as outlined in the reference document, without changing the Update Status, QMAX Cycle Count, or Cycle Count. The values remained 0E, 2, and 2, respectively.

3. The third golden image was generated after completing the final discharge, but this time, we updated the Update Status, QMAX Cycle Count, and Cycle Count to 02, 0, and 0, respectively.

Could you please advise which of these golden images would be most appropriate, or if we should make adjustments to any of them to better align with your specifications? We didn’t generate the golden image in the exact manner you described (with Update Status 0E, QMAX Cycle Count 0, and Cycle Count 0).

We would greatly appreciate your insights and recommendations on this matter.

Regards,

Devika

Hi Adrian,

Thank you for the information, as well as for your continuous technical support and dedication, which have been essential in helping us overcome the challenges encountered during the learning cycle of the fuel gauge.

Regards,

Devika

Hello Devika,

Your welcome, glad I was able to help!

Regards,

Adrian