BQ27520-G4: Incorrect SOC & SOH Readings

Stephanie Hiszpanski

Part Number: BQ27520-G4

Hello,

I was able to successfully generate a Chem ID and updated Ra tables for our BQ27520 using this TI app note. Unfortunately we have noticed a few discrepancies in our readings -

1. State of Charge:

With a fully discharged battery this value jumps from 0 to 100 in ~2minutes after charging begins. Same with fully charged and discharging (100 to 0 in ~2mins). This does not seem right?

2. State of Health:

This value never changes from 48% when testing on a new cell. This seems low? How often should this update?

Below are the Chem ID results and I have attached the .gg file with our Ra values. Can you please let me know if anything looks incorrect for our 2000mAhr 4.2V Lithium-ion Polymer (LIP) cell?

Best chemical ID : 256 Best chemical ID max. deviation, % : 2.88

Summary of all IDs with max. DOD deviation below 3%

Chem ID max DOD error, % Max R deviation, ratio

256 2.88 0.59

BQ27520_20221025.gg.csv

over 1 year ago

0 Shirish over 1 year ago

TI__Guru 57747 points

Hello Stephanie,

Can you elaborate on whether you had a successful learning cycle for Ra Table updates?

The bq27520 has slightly different parameters and this is the correct reference for it.

0 Stephanie Hiszpanski over 1 year ago in reply to Shirish

Prodigy 20 points

Hello,

Yes, I believe it had a successful learning cycle as the values in Ra0 Table updated (though this took me about 5-6 cycles before I was able to get it to update). I then copied those values to all other Raxx fields as shown in the .gg file I attached.

Ra0 Default
Ra1 Default
Ra0 Table <-- This is the only one that updated during the learning cycle
Ra1 Table
Ra0x Table
Ra1x Table

I was using the application note you referenced but someone else on this forum told me to use slua777 instead.

0 Shirish over 1 year ago in reply to Stephanie Hiszpanski

TI__Guru 57747 points

Hello Stephanie,

It is ok to use other documents for reference as there is more detail there. The goal is to have successful learning. I don't see Update status reflecting the learning, that is why i asked.

Also a new cell must show 100% SOH as it is the one used for learning.

0 Stephanie Hiszpanski over 1 year ago in reply to Shirish

Prodigy 20 points

Thank you. It sounds like the Ra Tables did not update correctly then if the Update Status does not reflect this. I will try to do the charge/discharge cycles again. When the Ra Table updates correctly, will the Update Status of the BQ27520 change to 02 and then persist?

0 Shirish over 1 year ago in reply to Stephanie Hiszpanski

TI__Guru 57747 points

Hello Stephanie,

Yes, once update status changes to 02, read out the image(similar process to reading golden image) so that you have a good reference point for comparison.

Power management

Power management forum

BQ27520-G4: Incorrect SOC & SOH Readings