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STC3117

Functional description

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6.2

STC3117 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

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-m

Ωsense 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 CC_CNF that is calculated as shown in

Equation 1:

Equation 1

Rsense is in m

Ω and Cnom is in mAh.

Example: Rsense =10 m

Ω, Cnom = 1500 mAh, CC_CNF = 303

REG_CURRENT

register

register

REG_COUNTER

16-bit counter

REG_CC_CNF

register

AD converter

EOC

CS

GND

current filter

To SOC

management

Coulomb counter

calculator

REG_AVG_CURRENT

register

CC_CNF

Rsense

Cnom

×

49.556

⁄

=