BQ40Z50-R2: High DOD Deviation (10%+) in LFP Chem ID Matching for BQ40Z50 (Using GPCCHEM)

Hello,

I am currently trying to find the best Chemical ID (Chem ID) for a Lithium Iron Phosphate (LFP) battery pack, which is managed by the BQ40Z50 gas gauge. I am using the TI GPCCHEM tool to analyze my relaxation log data, but I am consistently encountering very high maximum Depth of Discharge (DOD) errors.

After several attempts, my best Chem ID matches all show a maximum DOD error over 10%.

The search results summary (filtered for max DOD deviation below 15%) is as follows:    

Questions Specific to LFP and BQ40Z50:

1. Is it common for LFP cells to have maximum DOD deviations this high when using the BQ40Z50 GPCCHEM tool, especially given the cell's very flat Open Circuit Voltage (OCV) profile?

2. I understand that a DOD error of 3% or less is usually recommended for accurate State-of-Charge (SOC) gauging. Have other customers using the BQ40Z50 encountered similar issues where the best match is significantly above this 3% target?

3. What are the most critical factors or potential pitfalls I should pay attention to during the charge/discharge logging cycle to improve the results for LFP and the BQ40Z50? (e.g., specific relaxation times, current rates, temperature stability, or initial Qmax setup)

   • (Revised) My data collection followed the LFP procedure (Charge to full $\rightarrow$ Relax $\rightarrow$ Discharge to terminate $\rightarrow$ Relax). I ensured the relaxation periods were more than 5 hours (following TI's LFP recommendation), but I am still seeing high errors. Should the relaxation time be even longer for this cell's specific OCV characteristics?

Any advice on troubleshooting this high deviation or determining the necessity of generating a custom Chem ID (Alt ID) for the BQ40Z50 would be greatly appreciated.

Thank you!