STC3115 Datasheet, PDF (13/31 Pages) STMicroelectronics – Gas gauge IC with alarm output for handheld applications

STC3115
Functional description
6.2
6.2.1
STC3115 gas gauge architecture
Coulomb counter
The Coulomb counter is used to track the SOC of the battery when the battery is charging or
discharging at a high rate. Each current conversion result is accumulated (Coulomb
counting) for the calculation of the relative SOC value based on the configuration register.
The system controller can control the Coulomb counter and set and read the SOC register
through the I²C control registers.
Figure 5. Coulomb counter block diagram
EOC
CG
AD converter
GND
16-bit counter
CC SOC
calculator
REG_COUNTER
register
REG_CURRENT
register
CC SOC
register (internal)
REG_CC_CNF
register
The REG_CC_CNF value depends on battery capacity and the current sense resistor. It
scales the charge integrated by the sigma delta converter into a percentage value of the
battery capacity. The default value is 395 (corresponding to a 10-mΩ sense resistor and
1957-mAh battery capacity).
The Coulomb counter is inactive if the VMODE bit is set, this is the default state at power-
on-reset (POR) or reset (VMODE bit = 1).
Writing a value to the register REG_SOC (mixed mode SOC) forces the Coulomb counter
gas gauge algorithm to restart from this new SOC value.
REG_CC_CNF register is a 16-bit integer value and is calculated as shown in Equation 1:
Equation 1
REG_CC_CNF = Rsense × Cnom ⁄ 49.556
Rsense is in mΩ and Cnom is in mAh.
Example: Rsense =10 mΩ, Cnom = 1650 mAh, REG_CC_CNF = 333
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