BQ27541: Updating of RA Tables

Ryan McCracken

Part Number: BQ27541

Hello, I am working with the BQ27541 fuel gauge, and I was looking at the data memory for several of some battery modules which utilize this chip, and all of them had recorded either having undergone 0 or 1 charging cycles, but having take anywhere from 86 to 518 samples of the batteries OCV and other chemical and current characteristics of the cells, the RA tables for all but one of them looked identical to what I believe was originally flashed into the memory for the tables during initial manufacture, My question is when does the impedance tracking algorithm update the RA tables, does the updating algorithm depend on a successful charge cycle or on just a resting period after discharge or if there is significant difference to the values in the tables.

over 2 years ago

0 Shirish over 2 years ago

TI__Guru 57697 points

Hello Ryan,

The Ra tables are updated at fixed grid points during discharge. Each battery will have slightly different values for Ra once it is put into use.

0 Ryan McCracken over 2 years ago in reply to Shirish

Prodigy 10 points

So charging cycles don't impact the updating of the RA table, just the discharge during usage. Then why do the tables remain identical to each other after field usage of anywhere from 3 months to 3 years.

0 Ryan McCracken over 2 years ago in reply to Shirish

Prodigy 10 points

Also, where are these grid points located that cause these updates, how many cycles must the fuel gauge experience before it updates.

0 Shirish over 2 years ago in reply to Ryan McCracken

TI__Guru 57697 points

Hello Ryan,

Did you enable IT and complete a successful learning cycle on the pack?

0 Ryan McCracken over 2 years ago in reply to Shirish

Prodigy 10 points

I was not the one who did the initial learning of the batteries, but according to the Update status it's set to 6 to enable the IT for the RA table Updates

0 Ryan McCracken over 2 years ago in reply to Ryan McCracken

Prodigy 10 points

Does Chem ID affect the calculation for the RA tables, say if the battery ID it had was for a more energy dense battery, but the actual battery was a lower capacity battery, would that cause the IT to tabulate negative values for the RA table.

0 Shirish over 2 years ago in reply to Ryan McCracken

TI__Guru 57697 points

Hello Ryan,

There are many checks to prevent negative Ra values in the gauge. The battery capacity and chemistry must match for accurate gauging.

Ra values are stored in Ra and Rax tables. Writes to these table are delayed and grouped to avoid flash wearout. I recommend that you run a full charge discharge to check the accuracy rather than looking for RA changes

0 Ryan McCracken over 2 years ago in reply to Shirish

Prodigy 10 points

I was able to charge and discharge several times and the tables updated their values and they were very different from the initial values at lower charge levels. I know the users weren't properly cycling them to track the RA Tables. I think that the batteries were exposed to high heat levels prior to assembly and that it is reducing their capacity and increasing the resistance.

0 Shirish over 2 years ago in reply to Ryan McCracken

TI__Guru 57697 points

Hello Ryan,

High heat conditions can result in larger change of Ra values. I think the gauge is working fine and would encourage you to check if the battery provides the power that it says the battery can deliver.

0 Ryan McCracken over 2 years ago in reply to Shirish

Prodigy 10 points

The Batteries aren't delivering what they are rated to, this has helped me to sort out the issue with them.

0 Ryan McCracken over 2 years ago in reply to Shirish

Prodigy 10 points

There was an issue with the batteries not delivering what they are supposed to, and this helped confirm a diagnosis, thanks again.

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BQ27541: Updating of RA Tables