Datasheet

DS2780 Standalone Fuel Gauge IC
13 of 31
Figure 12. Cell Model Example Diagram
0°C 10°C 20°C 30°C 40°C
100%
1
2
3
4
Derivative
[ppm / °C]
Active
Em
p
t
y
Standby
Em
p
t
y
FULL
Cell
Characterization
data points
Full: The Full curve defines h
ow the full point of a given cell depends on temperature for a given charge
termination. The application’s charge termination method should be used to determine the table values. The
DS2780 reconstructs the Full line from the cell characteristic table to determine the Full capacity of the battery at
each temperature. Reconstruction occurs in one-degree temperature increments.
Active Empty: The Active Empty curve defines the variation of the Active Empty Point over temperature. The
Active Empty Point is defined as the minimum voltage required for system operation at a discharge rate based on a
high level load current (one that is sustained during a high power operating mode). This load current is
programmed as the Active Empty current (IAE) and should be a 3.5s average to correspond to values read from
the Current register. The specified minimum voltage, or Active Empty voltage (VAE), should be a 220ms average
to correspond to values read from the Voltage register. The DS2780 reconstructs 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 PDA applications, Standby Empty represents the point that
the battery can no longer support RAM refresh and thus the standby voltage is set by the RAM 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 on a wireless handset. The standby
load current and voltage are used for determining the cell characteristics but are not programmed into the DS2780.
The DS2780 reconstructs the Standby Empty line from the cell characteristic table to determine the Standby Empty
capacity of the battery at each temperature. Reconstruction occurs in one-degree temperature increments.