Rainbow Electronics DS2778 - Manual (Page 20)

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 four segments for each
model curve are stored in the cell parameter EEPROM
block as ppm/°C. The breakpoint temperatures of each
segment are stored there also (refer to Application Note
3584:
Storing Battery Fuel Gauge Parameters in
DS2780 for more details on how values are stored). An
example of data stored in this manner is shown in
Table 3.
Application Parameters
In addition to cell model characteristics, several appli-
cation 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 (1/
Ω). RSNSP supports resistor values of 1Ω to
3.922m
Ω. RSNSP is located in the parameter EEPROM
block.
RSNSP = 1/R SNS (units of mhos; 1/ Ω)
Charge Voltage (VCHG)
VCHG stores the charge voltage threshold used to
detect a fully charged state. The voltage is stored as a
1-byte value with units of 19.5mV and can range from 0
to 4.978V. VCHG should be set marginally less than the
average cell voltage at the end of the charge cycle to
ensure reliable charge termination detection. VCHG is
located in the parameter EEPROM block.
DS2775/DS2776/DS2777/DS2778
2-Cell, Stand-Alone, Li+ Fuel-Gauge IC with
Protector and Optional SHA-1 Authentication
20 ______________________________________________________________________________________
TEMPERATURE
CELL MODEL
PARAMETERS
(EEPROM)
LOOKUP
FUNCTION
FULL(T)
AE(T)
SE(T)
Figure 15. Lookup Function Diagram
Manufacturer’s Rated Cell Capacity: 1000mAh
Charge Voltage: 4.2V Termination Current: 50mA
Active Empty (V): 3.0V Standby Empty (I): 300mA
Sense Resistor: 0.020
SEGMENT BREAKPOINTS
TBP12 = -12°C
TBP23 = 0°C
TBP34 = 18°C
CALCULATED VALUE
+40°C NOMINAL
(mAh)
SEGMENT 1
(ppm/°C)
SEGMENT 2
(ppm/°C)
SEGMENT 3
(ppm/°C)
SEGMENT 4
(ppm/°C)
Full 1051 3601 3113 1163 854
Active Empty 2380 1099 671 305
Standby Empty 1404 427 244 183
Table 3. Example Cell Characterization Table (Normalized to +40°C)