DS2780 Maxim Integrated Products, DS2780 Datasheet - Page 13

• Manufacturer Part Number: DS2780
• Description: Stand-Alone Fuel Gauge IC
• Manufacturer: Maxim Integrated Products

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CELL MODEL CONSTRUCTION
The model is constructed with all points normalized to the fully charged state at +40°C. Initial values, the +40°C
Full value in mVh units and the +40°C Active Empty value as a fraction of the +40°C Full are stored in the cell
parameter EEPROM block. 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 also stored in the cell parameter EEPROM block.
Segment endpoints are fixed at 0°C, +10°C, +20°C, +30°C and +40°C. An example of data stored in this manner is
shown in Table 1.
Table 1. Example Cell Characterization Table (Normalized to +40°C)
Manufacturers rated cell capacity: 1000mAh
Charge Voltage: 4.2V
Active Empty (V, I): 3.0V, 300mA
Sense Resistor: 0.020W
Full
Active Empty
Standby Empty
Figure 12. Lookup Function Diagram
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.
Sense Resistor Prime (RSNSP): RSNSP stores the value of the sense resistor for use in computing the absolute
capacity results. The value is stored as a 1-byte conductance value with units of mhos. RSNSP supports resistor
values of 1W to 3.922mW. RSNSP is located in the Parameter EEPROM block.
Charge Voltage (VCHG): VCHG stores the charge voltage threshold used to detect a fully charged state. The
value is stored as a 1-byte voltage with units of 19.52mV and can range from 0V to 4.978V. VCHG should be set
marginally less than the cell voltage at the end of the charge cycle to ensure reliable charge termination detection.
VCHG is located in the Parameter EEPROM block.
Minimum Charge Current (IMIN): IMIN stores the charge current threshold used to detect a fully charged state.
The value is stored as a 1-byte value with units of 50mV and can range from 0 to 12.75mV. Assuming RSNS =
20mW, IMIN can be programmed from 0mA to 637.5mA in 2.5mA steps. IMIN should be set marginally greater than
the charge current at the end of the charge cycle to ensure reliable charge termination detection. IMIN is located in
the Parameter EEPROM block.
Temperature
Parameters
(EEPROM)
Cell Model
15 bytes
+40°C
Nominal
[mAh]
1051
Charge Current: 500mA
0.927
0.051
0.013
0°C
Function
Lookup
0.0067
+10°C
0.951
0.040
Standby Empty (V, I): 3.0V, 4mA
13 of 27
0.0038
Termination Current: 50mA
+20°C
0.974
0.022
FULL(T)
SE(T)
AE(T)
+30°C
0.991
0.012
0.001
DS2780 Stand-Alone Fuel Gauge IC
+40°C
0.008
1.0
0