DS2778 Maxim Integrated Products, DS2778 Datasheet - Page 21

• Manufacturer Part Number: DS2778
• Description: 2-Cell Stand-Alone Li+ Fuel-Gauge IC
• Manufacturer: Maxim Integrated Products

full with a resolution of 2
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.
Figure 15. Lookup Function Diagram
Table 3. Example Cell Characterization Table (Normalized to +40°C)
Manufacturer’s Rated Cell Capacity: 1000mAh
Charge Voltage: 4.2V
Active Empty (V): 3.0V
Sense Resistor: 0.020
TBP12 = -12°C
TBP23 = 0°C
TBP34 = 18°C
Full
Active Empty
Standby Empty
CALCULATED VALUE
TEMPERATURE
PARAMETERS
CELL MODEL
Protector and Optional SHA-1 Authentication
(EEPROM)
SEGMENT BREAKPOINTS
2-Cell, Stand-Alone, Li+ Fuel-Gauge IC with
______________________________________________________________________________________
-10
FUNCTION
LOOKUP
+40°C NOMINAL
. Standby empty at +40°C is,
(mAh)
1051
FULL(T)
AE(T)
SE(T)
SEGMENT 1
(ppm/°C)
3601
2380
1404
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.
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
3.922mΩ. RSNSP is located in the parameter EEPROM
block.
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.
Termination Current: 50mA
Standby Empty (I): 300mA
SEGMENT 2
(ppm/°C)
3113
1099
427
RSNSP = 1/R
Sense Resistor Prime (RSNSP)
Application Parameters
SEGMENT 3
SNS
(ppm/°C)
1163
Charge Voltage (VCHG)
671
244
(units of mhos; 1/Ω)
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SEGMENT 4
(ppm/°C)
854
305
183
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