BQ27421-G1: bq27421-G1 Gauging Parameter Calculator

Hello Wyatt Keller,

I’m aware that BQ27421-G1B does not have FLASH memory. The fuel gauge is always connected to the battery(whole device lifetime), and all the configuration data is stored in the ROM of the IC, unless the battery gets disconnected by the protection circuitry for some reason. If reset is detected - the host device provides configuration data to the IC immediately.

The main problem is - when the device is exposed to low temperatures(anything below 0°С - -5°С) the fuel gauge starts to show percentage drop/swing after some time (check the logs in my previous post: https://e2e.ti.com/support/power-management/f/196/t/973208). Usually the workflow is like this: when some significant amount of current is drained from the battery(around 0,2-0,3 Amperes) for 10 seconds usually, and up to 60 seconds, there is a voltage drop(up to 0,5 Volts). As a result the battery voltage recovers to the previous magnitude, but the percentage value on the fuel gauge IC is kept near the lowest reading. 

For example: the environment temperature is -5°С, the battery is at 50% (3,8 Volts), then for 30 seconds 0,25 Amperes is drained by the system, and the voltage drops from 3,8 Volts to 3,3 Volts. Also the battery percentage on the fuel gauge IC descends to 0%. After some time the initial battery voltage is slowly restored to a close value before the load event, but the percentage stays at 0% forever, unless you start charging the device.

I had already executed these tests, recommended in my previous topic:

https://www.ti.com/tool/GPCRB

https://www.ti.com/tool/GPCRA0

But unfortunately after uploading the test results I always get error reports… (see test results screenshots above in the beginning of this topic)

What am I doing wrong?

I need to know how to configure the fuel gauge in order to work correctly at low temperatures. What parameters like Qmax, Ra, and Thermal coefficients should I change from the default values?

Best regards,

Michael

Hello Wyatt Keller,

Thanks for your reply. 

Yes, I'm using the smoothing feature. It is enabled by default. I didn't change it.

From datasheet:

From FG config:

I’m still not sure what I have to do, because you don't answer most of my questions.

1. How can I fix the percentage drop/swing? I need to have a stable percentage behavior on the fuel gauge in different environment temperatures.

2. How can I do it with the current fuel gauge (BQ27421-G1B)? What parameters like Qmax, Ra, TermV Valid t, T Rise, T Time Constant and Thermal coefficients should I change from the default values?

3. Why did my tests fail? (GPCRB and GPCRA0)

Best regards,

Michael

Hi Michael,

GPCRB and GPCRA0 are failing because it is a ROM gauge. There is a workaround but you would have to upload the gm.fs file everytime the gauge losses power.

Best regards,

Hi Nick,

Yes, correct, every time the FG is losing its power we will reconfigure it.

The remaining questions are:
1. Which parameters we need to change for using it at low temperature (several logs were made already in different temperature with bqStudio)
- see test results screenshots above in the beginning of this topic and
- check the logs in my previous post: https://e2e.ti.com/support/power-management/f/196/t/973208

2. How can we calculate those parameters?

Best regards,
Michael

Hi Michael,

We are working on this you can expect an update by end of the week.

Best regards,

Hi Nick,

I'm using this fuel gauge config: 
1884.gg.csv

Best regards,
Michael