DS2784 Maxim Integrated Products, DS2784 Datasheet - Page 18

• Manufacturer Part Number: DS2784
• Description: 1-Cell Stand-Alone Fuel Gauge IC
• Manufacturer: Maxim Integrated Products

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Figure 3. Cell Model Example Diagram
Full—The full curve defines how the full point of a given cell varies over temperature for a given charge termination.
The application’s charge termination method should be used to determine the table values. The DS2784
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 value to correspond to values read
from the current register. The specified minimum voltage, or active empty voltage (VAE), should be a 220ms
average value to correspond to the values read from the voltage register. The DS2784 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 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 determining the cell characteristics but are not programmed into the DS2784. The DS2784
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.
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 µVhr with an LSB of 6.25µVhr. The +40°C active
empty value is stored as a percentage of +40°C full with a resolution of 2
definition, zero and, therefore, no storage is required. The slopes (derivatives) of the 4 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 (see 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 6.
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication
SEGMENT 1
DERIVATIVE
[PPM/°C]
TBP12
SEG. 2
18 of 37
TBP23
SEG. 3
ACTIVE
EMPTY
STANDBY
EMPTY
FULL
TBP34
SEG. 4
-10
. Standby empty at +40°C is, by
40°C
CELL
CHARACTERIZATION
DATA POINTS
SEG. 5