STC3115 Datasheet, PDF (11/31 Pages) STMicroelectronics – Gas gauge IC with alarm output for handheld applications

STC3115
6
Functional description
Functional description
6.1
6.1.1
6.1.2
Battery monitoring functions
Operating modes
The monitoring functions include the measurement of battery voltage, current, and
temperature. A Coulomb counter is available to track the SOC when the battery is charging
or discharging at a high rate. A sigma-delta A/D converter is used to measure the voltage,
current, and temperature.
The STC3115 can operate in two different modes with different power consumption (see
Table 8. Mode selection is made by the VMODE bit in register 0 (refer to Table 13 for
register 0 definition).
Table 8. STC3115 operating modes
VMODE
Description
0
Mixed mode, Coulomb counter is active, voltage gas gauge runs in parallel
1
Voltage gas gauge with power saving
Coulomb counter is not used. No current sensing.
In mixed mode, current is measured continuously (except for a conversion cycle every 4 s
and every 16 s seconds for measuring voltage and temperature respectively). This provides
the highest accuracy from the gas gauge.
In voltage mode with no current sensing, a voltage conversion is made every 4 s and a
temperature conversion every 16 s. This mode provides the lowest power consumption.
It is possible to switch between the two operating modes to get the best accuracy during
active periods, and to save power during standby periods while still keeping track of the
SOC information.
Battery voltage monitoring
Battery voltage is measured by using one conversion cycle of the A/D converter every 4 s.
The conversion cycle takes 2¹³ = 8192 clock cycles. Using the 32768 Hz internal clock, the
conversion cycle time is 250 ms.
The voltage range is 0 to 4.5 V and resolution is 2.20 mV. Accuracy of the voltage
measurement is ±0.5% over the temperature range. This allows accurate SOC information
from the battery open-circuit voltage.
The result is stored in the REG_VOLTAGE register (see Table 12).
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