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STC3115

Functional description

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6.2.3

Mixed mode gas gauge system

The STC3115 provides a mixed mode gas gauge using both a Coulomb counter (CC) and a

voltage-mode (VM) algorithm to track the SOC of the battery in all conditions with optimum

accuracy. The STC3115 directly provides the SOC information.

The Coulomb counter is mainly used 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 a configuration register.

The voltage-mode algorithm is used when the application is in low power consumption state.

The STC3115 automatically uses the best method in any given application condition.

However, when the application enters standby mode, the STC3115 can be put in power-

saving mode: only the voltage-mode gas gauge stays active, the Coulomb counter is

stopped and power consumption is reduced.

Figure 7. Mixed mode gas gauge block diagram

The combination of the CC and VM algorithms provides optimum accuracy under all

application conditions. The voltage gas gauge cancels any long-term errors and prevents

the SOC drift problem that is commonly found in Coulomb counter only solutions.

Furthermore, the results of the two algorithms are continuously compared and adjustment

factors are calculated. This enables the application to track the CC and VM algorithm

parameters for long-term accuracy, automatically compensating for battery aging,

application condition changes, and temperature effects. Five registers are dedicated to this

monitoring:

•

REG_CC_ADJ and REG_VM_ADJ are continuously updated. They are signed, 16-bit,

user-adjusted registers with LSB = 1/512 %.

•

ACC_CC_ADJ and ACC_VM_ADJ are updated only when a method switch occurs.

They are signed, 16-bit user adjusted accumulators with LSB = 1/512%

•

RST_ACC_CC_ADJ and RST_ACC_VM_ADJ bits in the REG_MODE register are

used to clear the associated counter.

Voltage mode

(VM)

REG_SOC

register

Alarm

management

Parameter

tracking

Coulomb

counter

REG_VM_ADJ

register

REG_CC_ADJ

register

gas gauge

(CC)

SOC

management