STC3115AIJT datasheet(13/31 Pages) STMICROELECTRONICS

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STC3115

Functional description

6.2

STC3115 gas gauge architecture

6.2.1

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

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

Rsense is in mΩ and Cnom is in mAh.

Example: Rsense =10 mΩ, Cnom = 1650 mAh, REG_CC_CNF = 333

CC SOC

REG_CURRENT

REG_COUNTER

16-bit counter

REG_CC_CNF

CC SOC

calculator

AD converter

EOC

GND

REG_CC_CNF

Rsense Cnom

49.556

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