STC3117 Datasheet, PDF (14/34 Pages) STMicroelectronics – Gas gauge IC with battery charger control for handheld applications

Functional description
STC3117
6.2.2
Voltage gas gauge algorithm
No current sensing is needed for the voltage gas gauge. An internal algorithm precisely
simulates the dynamic behavior of the battery and provides an estimation of the OCV. The
battery SOC is related to the OCV by means of a high-precision reference OCV curve built
into the STC3117.
Any change in battery voltage causes the algorithm to track both the OCV and SOC values,
taking into account the non-linear characteristics and time constants related to the chemical
nature of the Li-Ion and Li-Po batteries.
A single parameter fits the algorithm to a specific battery. The default value provides good
results for most battery chemistries used in hand-held applications.
Figure 6. Voltage gas gauge block diagram
REG_VOLTAGE
register
REG_VM_CNF
register
VIN
AD
converter
Voltage mode
(VM)
algorithm
REG_OCV
register
To SOC
management
14/34
Reference
OCV
curve
REG_OCVTAB
register
REG_SOCTAB
register
Voltage gas gauge algorithm registers
The REG_VM_CNF configuration register is used to configure the parameter used by the
algorithm based on battery characteristic. The default value is 321 (corresponding to
160 mΩ internal battery impedance and 1957 mAh Cnom battery capacity).
The REG_OCV register holds the estimated OCV value corresponding to the present
battery state.
The REG_OCVTAB and REG_SOCTAB registers define the OCV curve for a given battery
type; the default power-up values can be updated at software initialization.
The REG_VM_CNF register is a 12-bit integer value and is calculated from the averaged
internal resistance and nominal capacity of the battery as shown in Equation 2:
Equation 2
VM_CNF = Ri × Cnom ⁄ 977.78
Ri is in mΩ and Cnom is in mAh.
Example: Ri = 250 mΩ, Cnom =1500 mAh, VM_CNF= 384
DocID025792 Rev 2