Rainbow Electronics DS2778 - Manual (Page 19)

DS2775/DS2776/DS2777/DS2778
2-Cell, Stand-Alone, Li+ Fuel-Gauge IC with
Protector and Optional SHA-1 Authentication
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100%
SEGMENT 1
DERIVATIVE
(ppm/ °C)
FULL
ACTIVE
EMPTY
STANDBY
EMPTY
SEGMENT 2 SEGMENT 3 SEGMENT 4
+40 °C TBP34 TBP23 TBP12
SEGMENT 5
CELL
CHARACTERIZATION
CELL
CHARACTERIZATION DATA
Figure 14. Cell Model Example Diagram
read from the Current register. The specified minimum
voltage, or active-empty voltage (VAE), should be a
110ms average value to correspond to the values read
from the voltage register. The VAE value represents the
average of the two cell’s voltages, V
IN1 and V IN2 . The
DS2775–DS2778 reconstruct the active-empty line from
the cell characteristic table to determine the active-
empty capacity of the battery at each temperature.
Reconstruction occurs in one-degree temperature
increments.
Standby Empty
The standby-empty curve defines the variation of the
standby-empty point over temperature. The standby-
empty point is defined as the minimum voltage required
for standby operation at a discharge rate dictated by
the application standby current. In typical handheld
applications, standby empty represents the point that
the battery can no longer support DRAM refresh and
thus the standby voltage is set by the minimum DRAM
voltage-supply requirements. In other applications,
standby empty can represent the point that the battery
can no longer support a subset of the full application
operation, such as games or organizer functions. The
standby-load current and voltage are used for deter-
mining the cell characteristics but are not programmed
into the DS2775–DS2778. The DS2775–DS2778 recon-
struct the standby-empty line from the cell characteris-
tic table to determine the standby-empty capacity of
the battery at each temperature. Reconstruction occurs
in one-degree temperature increments.
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 µVh with an LSb of 6.25µVh. The +40°C
active-empty value is stored as a percentage of +40°C