Datasheet
DS2782
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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 DS2782. The DS2782 reconstructs the Standby Empty line
from cell characteristic table values 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. 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 Charge Current: 500mA Termination Current: 50mA
Active Empty (V, I): 3.0V, 300mA Standby Empty (V, I): 3.0V, 4mA
Sense Resistor: 0.020
+40C
Nominal
[mAh]
0°C +10°C +20°C +30°C +40°C
Full 1051 0.927 0.951 0.974 0.991 1.0
Active Empty 0.051 0.040 0.022 0.012 0.008
Standby Empty 0.013 0.0067 0.0038 0.001 0
Figure 13. Lookup Function Diagram
Cell Model
Parameters
15 bytes
(EEPROM)
Temperature
Lookup
Function
FULL(T)
AE(T)
SE(T)