Datasheet

DS2780 Standalone Fuel Gauge IC
14 of 31
CELL MODEL CONSTRUCTION
The model is constructed with all points normalized to the fully charged state at +40°C. All values are stored in the
cell parameter EEPROM block. The +40°C Full value is stored in uVhr with an LSB of 6.25uVhr. The +40°C Active
Empty value is stored as a percentage of +40°C Full with a resolution of 2
-10
. Standby Empty at +40°C is by
definition zero and therefore no storage is required. The slopes (derivatives) of the 4 segments for each model
curve are stored in the cell parameter EEPROM block as PPM/°C. Segment endpoints are fixed at 0°C, +10°C,
+20°C, +30°C and +40°C. (See Application Note 3584 for more details on how values are stored.) An example of
cell model data is shown in Table 1a. Table 1b shows the actual data values stored in memory.
Table 1a. Example Cell Characterization Table (Normalized to +40°C)
Rated cell capacity: 1000mAh
Charge Voltage: 4.2V Terminating Current: 50mA
Active Empty (V): 3.0V Active Empty (I): 300mA
Sense Resistor: 0.020
+40C
Nominal
[mAh]
0°C +10°C +20°C +30°C +40°C
Full 1051 0.927 0.951 0.974 0.991 1.0
Active Empty 0.051 0.040 0.022 0.012 0.008
Standby Empty 0.013 0.0067 0.0038 0.001 0
Table 1b. Example Cell Characterization Table (Actual data values stored in EEPROM)
Rated cell capacity: 0C80h
Charge Voltage: D7h Terminating Current: 14h
Active Empty (V): 9Ah Active Empty (I): 1Eh
Sense Resistor: 32h
+40C
Nominal
[mAh]
0°C +10°C +20°C +30°C +40°C
Full 0D32h 27h 26h 1Ch 0Fh 0D32h
Active Empty 12h 1Eh 10h 07h 08h
Standby Empty 0Ah 05h 05h 02h
Figure 13. Lookup Function Diagram
Cell Model
Parameters
15 bytes
(EEPROM)
Temperature
Lookup
Function
FULL(T)
AE(T)
SE(T)
APPLICATION PARAMETERS
In addition to cell model characteristics, several application parameters are needed to detect the full and empty
points, as well as calculate results in mAh units.