BQ40Z50-R1: BQ40Z50-R1 current calibration incorrect after power cycle.

Hello Sidney,

You shouldn't need to run another calibration after a power cycle, the bq40z50 is a flash based gauge so all the values are saved.

Can you share a log of the incorrect current values? How long are the current values incorrect after a POR, and have you ruled out any communication errors?

Sincerely,

Wyatt Keller

Hi Wyatt,

Thank you for your reply. We notice this issue around NOV-2020, and the report from production there are 150~200ma different after current calibration during the post-testing. We have our own software (Labview) to run the calibration, and we did read the calibrated value after calibration, and the results are all correct (Voltage, temperature and current).

We have been used this method (Labview) for over two years and we haven't seen anything like this. Also, I read the CC and Capacity gain from the BQ studio for fail calibration fuel gauge pcba, and both values are 3.2xx (mOhm), and the good calibration fuel gauge reads 3.0xx (mOhm).

Our process for post-assembly and testing could be with an hour or day after the fuel gauge calibrated.

Thanks,

Hi Wyatt,

We use the same method to calibrate over 20,000 Fuel gauge PCBA assembly without the problem until recently. But we only see 1% of the fuel gauge has this issue amount the 200 fuel gauge assembly. Also, we have multiple stations for the fuel gauge, and it randomly happening at different stations. All stations are individual.

Here is a step for our current calibration. 

1. Read constant resistance current from the DMM, and making sure the reading is -1500ma

2. Read the fuel gauge current reading

3. Calculate the cc gain and capacity gain

4. Send a calculated gain value to the fuel gauge

5. wait for few seconds

6. Read the  DAStatus1 (current section)

7. Compare with our tolerance.

Thanks,

Sidney

Hi Wyatt,

If I re-calibrate the gauge with the entire assembly (cell-attached) by BQ, I don't see any problem at all.

I was looking at the technical reference document, the default CC gain was set on the 3.58422 on Revised January 2018, and our gauge is set on 1.036 (new version gg file from our customer). I am wondering if this value should close to the current sense resistor on the fuel gauge or doesn't matter at all?

Thank you.

Sidney

Hi Wyatt,

I did some test, before i read the cc gain and capacity gain back, I cycle the power for the fuel gauge, and I finally found one of 200 fuel gauge the calibration value jump from 3.0xx mohm to 3.2xx mohm. Not sure if this makes any sense to you.

Also, how did I convert the cc gain to mohm? I found some articles from E2E but I am not able to figure the result. can you explain a bit more detail for me?

what exactly this "x   where x is the value in the CC Gain flash" mean? 

CC Gain (mOhms) = 8.4391 / x   where x is the value in the CC Gain flash. The default value in this register is 0x84070275 which represents 8.4381 in Xemics floating point. 

Thanks,

Sidney

Hi Wyatt,

Thank you for the answer regarding the mOhm conversion. Also, is any chance you may let me know, how long will take the fuel gauge (DAStatus1) to update the new cc/ cap gain after the new value is written.

I believe we are narrow down the issue we have encounter right now, but we still try to understand when we read the current value from DAStatus1, it reports correct reading (example -1500mv), but after cycle the power, we actually read again, it returns1380ma only.

Again, Thank you for your help, this helps us lots to deal with our current issue.

Sidney

Hello Sidney,

Does this issue occur when you use bqStudio to calibrate? After you write the values they should be stored in the gauges flash after a POR. Is the current you're reading from DAStatus1 different than the Current() reading?

After a power cycle did the calibration data change?

Sincerely,

Wyatt Keller

Hi Wyatt,

First, to answer your question, I did not see any problem if I use BQ studio to do the calibration, only notice on our own test system. Also, I believe we found a issue today, but I am not sure if this is cause by our test system reading or gauge responding time.

Before we calibrate the current; we read currents 5 times from the gauge to get average current before we run the calibration. Most pre-calibrate currents value from the gauge is reading approximate 1250 ma, but we found one fuel gauge today it reads 1349 ma 5 times. That is why the calibration goes wrong because we use that pre-calibrate value to calculate the CC gain. That also explain when we reading back without the problem before power cycle.Not sure if that make sense to you.

We did wait for 5 seconds after we enable the constant resistance load (5 ohm), and 300 ms between each read, does that 5 seconds is enough time for gauge response the correct value? 

Thanks,

Sidney,

Hi Wyatt,

Yes, we are following the slua734a document, but we did not check "0" current on cc and board offset before we calibrate. I am not sure if this may cause the problem or not.

Both cc and board offset default set at "0", and that is why we did not check before we calibrate. Look like sometimes there are some currents or just fuel gauge faulty reading when fuel gauge power-up. 

Thanks,

Sidney