Hi all,
We're using the STC3115 for a single-cell lithium battery, the main goal is to provide a SoC that gives the user a feeling about remaining battery life.
This is working quite well when we're draining the battery completely, even in very different current consumption scenarios, the SoC goes down gradually as expected matching power consumption expectations.
However when we're charging the application the SoC reaches 99-100% at about 80% of the capacity of the battery, sometimes even a lot sooner.
When the application is removed from the charger this causes quite a lot of issues, since the SoC can be quite high due to RAM Restoration, showing a too high number to the user, which finds it annoying to see the application turn off at (for example) a displayed 60%.
Application details:
End-of-application / shutdown voltage: 3550mV
OCV curve: adapted to datasheet of battery manufacturer and checked with own measurements.
Impedance: should be around 200 mOhm, 400 mOhm was also tried.
Battery: Lithium ion battery (3.7V)
Capacity: 2300mAh
Charge current: up to 1000mA
Discharge current range: 150-350mA
To create graphical plots, to visualize the SoC issue, the application was forced to be on continuously (normally it turns of at 98%). Monitoring mode is mixed mode for full charge plot.
New battery:
Battery with ~200 charge/discharge cycles (normal charge speed)
Battery with ~200 charge/discharge cycles (slow charge speed due to input current limitation)
End-of-charge drop can be seen on all plots, in the green line displaying current. In all conditions the SoC reaches 100% too soon.
What should we change/monitor/calculate to improve these internal calculations?
Also how big is the influence of the Calculated OCV value on the SoC? Is it directly related like a look-up table, or is it one of many parameters leading to a SoC?
If more detail is needed about these charging sessions let me know, I can provide more detail (more is logged than displayed here, i.e. ConvC, AccAdjCC, etc).
