Software

AN4324

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DocID024963 Rev 2.0

6.5

STC3115 task procedure

The task software block reports the battery state. From a simple system status check to a

full battery report, the STC3115 task software block is called periodically at any frequency

to be in line with the system power consumption.

6.5.1

How often the STC3115 has to be called in run mode

A delay between two STC3115 accesses does not change the report accuracy. For

example, when the state of charge (SOC) is moving faster, an access delay can be scaled

by the application consumption to update more frequently the SOC reported to the user.

This can be achieved by using the REG_CURENT value. The STC3115 access delay can

also be decreased accordingly to the SOC level. The lower the SOC is, the lower the

access delay is.

Alternatively, the STC3115 can be accessed with a fixed period. A fixed period has to be in

line with application consumption and battery capacity. For example, the period could be

equal to a minimum delay of 1 % discharge:

(Battery capacity (mAh) / application maximum current (mA)) x 0.01 = STC3115 access

period (h).

By default, a delay of 30 seconds to 1 minute between two STC3115 accesses is

considered adequate for most standard applications.

During the periodic access to the STC3115, several simple checks have to be performed to

verify system stability. Consequently, the task function needs to read the STC3115 to

report the information to the system.

The application checks verify if any battery swaps or removal events have occurred since

checking the BATFAIL and PORDET bits. The RAM memory integrity can also be checked

to ensure chipset stability and reliability between two driver accesses. From these bits and

the RAM status, the driver can either report the updated battery status or it can restart and

reset the data in the exchange structure.

At the end of the task procedure, the exchange data structure has to be updated to report

the last battery status to the system. At this time, the RAM memory registers have also to

be updated to save their status for the next driver access.

An additional feature of this procedure is to track the application state. Based on current

and voltage measured values, charging, end of charging, idle, discharging, and low battery

status can also be reported to the system.

6.6

STOP procedure

To stop the device correctly if the application switches off, the GG_Run bit has to be

cleared. The RAM can also be updated with the last updated battery state. This information

can be used during the START procedure if the battery has not been removed.