Controller tasks for gas gauge implementation

AN3064

10/15

Doc ID 16263 Rev 1

3

Controller tasks for gas gauge implementation

The system controller manages the following tasks.

●

At start-up, it enables the STC3100’s battery monitoring functions.

●

It periodically reads the battery voltage, temperature, current and charge accumulator

and uses this information to estimate the state of charge.

●

At power-down, it disables the STC3100.

Figure 6.

Flow chart of the general gas gauge system

3.1

Application start-up

A typical startup code writes 0x02 (hex value) into the REG_CTRL register to reset the

accumulator and counter and clear the PORDET bit, and then 0x10 into the REG_MODE

register to start the STC3100 in 14-bit resolution mode.

The startup code then sets a periodic GasGauge task that will be called every 5 seconds.

3.2

Periodic GasGauge task

A simple periodic GasGauge task will do the following.

●

Read the battery voltage, temperature, current and charge accumulator.

●

At first call, use the battery voltage to estimate the battery’s state-of-charge and save it

in a RAM location of the STC3100 as a reference value.

●

During subsequent calls, use the saved reference value and the present charge

register content to calculate the present battery capacity:

battery capacity = reference value + charge register content.

●

Trigger a "low battery" alarm if the battery’s voltage is low (typically less than 3.1 V).

●

Calculate the remaining operating time from the remaining battery capacity and current

consumption when the battery is not charging (negative current).

3.3

Application power-down

The shutdown code puts the STC3100 in standby mode by writing 0 into the REG_MODE

register.

Application startup

Periodic task ‘GasGauge’

Application shutdown

Enable the STC3100

Set-up a periodic task ‘GasGauge’

Read the STC3100 data

Process the gas gauge system

Disable the STC3100

AM04582