Rainbow Electronics DS2784 - Manual (Page 18)

DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication
Figure 3. Cell Model Example Diagram
18 of 38
ull —The full curve defines how the full point of a given cell varies over temperature for a given charge termination.
ctive Empty —The active-empty curve defines the variation of the active-empty point over temperature. The
tandby Empty —The standby-empty curve defines the variation of the standby-empty point over temperature. The
ELL MODEL CONSTRUCTION
with all points normalized to the fully charged
TBP12 TBP23 TBP34 40°C
100%
SEGMENT 1
DERIVATIVE
[PPM/°C]
ACTIVE
EMPTY
STANDBY
EMPTY
FULL
CELL
CHARACTERIZATION
DATA POINTS
SEG. 2 SEG. 3 SEG. 4 SEG. 5
F
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.
A
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.
S
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.
C
The model is constructed
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
-10
. Standby empty at +40°C is, by definition, zero and
, therefore, no
storage is required. The slopes (derivatives) of the 4 segments for each