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STC3117

Functional description

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6.2.3

Mixed mode gas gauge system

Coulomb counter (CC) and the voltage mode (VM) algorithm to track the battery SOC in all

application conditions and automatically provide the optimum SOC information. The VM

algorithm cancels any long-term errors and prevents the SOC drift problem that is

commonly found in CC-only solutions.

The STC3117 automatically selects the best method based on the relaxation timer (see

Section 6.4: Current monitoring) as follows: when a low-power application state is detected

by the relaxation timer, the SOC reported by the STC3117 is the VM SOC, otherwise the CC

SOC is reported. The STC3117 manages the transitions between the VM and CC modes

without discontinuity by adjusting the VM and the CC SOC to ensure smooth SOC variations

without jumps in any application conditions.

The current mixed mode state is indicated by the GG_VM bit in the REG_CTRL register:

GG_VM=1 means the reported SOC is the VM SOC, otherwise the SOC is the CC SOC.

Note:

When the application enters standby mode, the STC3117 can be put into power-saving

mode by setting the VMODE bit to 1 in the REG_MODE register. Only the VM gas gauge

stays active, the CC is stopped, and the power consumption is reduced.

Figure 7. Mixed mode gas gauge block diagram

Adjustment registers

The registers REG_CC_ADJ and REG_VM_ADJ are signed 16-bit registers. They

accumulate the adjustment quantities made to the SOC values by the embedded mixed

mode algorithm:

•

REG_CC_ADJ = REG_SOC – (unadjusted CC SOC)

•

REG_VM_ADJ = REG_SOC – (unadjusted VM SOC)

These registers can be used by the system application to implement more sophisticated

algorithms for improved performance and accuracy.

Writing to the REG_SOC or REG_OCV initializes the two VM and CC algorithms to the

corresponding SOC value and clears REG_VM_ADJ and REG_CC_ADJ. It is possible to

write to the REG_SOC, REG_OCV, REG_VM_CNF and REG_CC_CNF registers when the

STC3117 is running without disturbing SOC management.

Note:

When writing to the REG_SOC or REG_OCV registers, the resulting SOC value is rounded

to the nearest 1/64 % value (the least three bits of REG_SOC are zero).

Voltage mode

(VM)

REG_SOC

register

Alarm

management

Parameter

tracking

Coulomb

counter

REG_VM_ADJ

register

REG_CC_ADJ

register

(CC)

SOC

management

gas gauge