ISL6295 Datasheet, PDF (24/25 Pages) Intersil Corporation – Low Voltage Fuel Gauge

ISL6295
Fuel Gauge Operation
The operation overview diagram in Figure 9 illustrates the
fuel gauge operation of the ISL6295. The ISL6295
incorporates four 32-bit accumulators and four 32-bit
elapsed time counters. The Charge Current Accumulator
(CCA) and Discharge Current Accumulator (DCA)
accumulate a measure of charge and discharge currents for
the capacity calculation and cycle count. The Charge Time
Counter (CTC) and Discharge Time Counter (DTC) are
intended to maintain the total charge time and discharge
time for the self-discharge, average charge, and discharge
currents over an extended period of time.
Input
Charge Current
Discharge Current
Voltage
Temperature
CCA
(Charge Current
Accumulator)
CTC
(Charge Time
Counter)
DCA
DTC
(Discharge Current (Discharge
Accumulator) Time Counter)
VPCtrl
(Voltage ADC)
ItCtrl/EtCtrl
(Temperature ADC)
ISL6295 IC
Host
Capacity Calculation
Delta_Capacity_Count = CCA - DCA
Delta_Time_Count = CTC + DTC
Gross_Capacity (mAh) = (Delta_Capacity_Count *
130µAs) / (1000 * 3600)
SelfDischarge_Loss (mAh) = SelfDischarge_LookupTable
[ItCtrl/EtCtrl] * ((Delta_Time_Count * 0.5)/3600)
Adjusted_Capacity = Gross_Capacity - SelfDischarge_Loss
NOTES: 1. 130µAs is the Accumulator LSB based upon 20mΩ sensor
resistor and 15-bit resolution;
2. The length of CCA, DCA, CTC, and DTC are 32-bit long;
3. CCA, DCA, CTC, and DTC will be updated every 0.5 second;
FIGURE 9. FUEL GAUGE OPERATION
24
FN9074.0
October 25, 2005