DS2788 MAXIM [Maxim Integrated Products], DS2788 Datasheet - Page 12

• Manufacturer Part Number: DS2788
• Description: Stand-Alone Fuel-Gauge IC with LED Display Drivers
• Manufacturer: MAXIM [Maxim Integrated Products]

Remaining capacity estimation uses real-time measured
values and stored parameters describing the cell char-
acteristics and application operating limits. Figure 11
describes the algorithm inputs and outputs.
To achieve reasonable accuracy in estimating remain-
ing capacity, the cell stack performance characteristics
over temperature, load current, and charge termination
Stand-Alone Fuel-Gauge IC with
LED Display Drivers
Figure 11. Top Level Algorithm Diagram
12
______________________________________________________________________________________
Capacity Estimation Algorithm
VOLTAGE
TEMPERATURE
CURRENT
ACCUMULATED
CURRENT (ACR) (RW)
AVERAGE CURRENT
AGING CAPACITY (AC)
(2 BYTES EE)
AGE SCALAR (AS)
(1-BYTE EE)
SENSE RESISTOR PRIME (RSNSP)
(1 -BYTE EE)
CHARGE VOLTAGE (VCHG)
(1-BYTE EE)
MINIMUM CHARGE CURRENT (IMIN)
(1-BYTE EE)
ACTIVE EMPTY VOLTAGE (VAE)
(1-BYTE EE)
ACTIVE EMPTY CURRENT (IAE)
(1-BYTE EE)
CELL PARAMETERS
(EEPROM)
16 BYTES
Modeling Cell Stack
Characteristics
(R)
(R)
(R)
(R)
AVAILABLE CAPACITY CALCULATION
ACR HOUSEKEEPING
CAPACITY LOOKUP
LEARN FUNCTION
AGE ESTIMATOR
point must be considered. Since the behavior of Li+
cells is nonlinear, these characteristics must be includ-
ed in the capacity estimation to achieve an acceptable
level of accuracy in the capacity estimation. The
FuelPack™ method used in the DS2788 is described in
general in Application Note AN131: Lithium-Ion Cell
Fuel Gauging with Dallas Semiconductor Battery
Monitor ICs . To facilitate efficient implementation in
hardware, a modified version of the method outlined in
AN131 is used to store cell characteristics in the
DS2788. Full and empty points are retrieved in a lookup
process that retraces piece-wise linear model consist-
FuelPack is a trademark of Dallas Semiconductor Corp., a
wholly owned subsidiary of Maxim Integrated Products, Inc.
FULL
ACTIVE EMPTY
STANDBY EMPTY SE(T)
REMAINING ACTIVE ABSOLUTE
CAPACITY (RAAC) mAh
REMAINING STANDBY ABSOLUTE
CAPACITY (RSAC) mAh
REMAINING ACTIVE RELATIVE
CAPACITY (RARC) %
REMAINING STANDBY RELATIVE
CAPACITY (RSRC) %
FULL(T)
AE(T)
(R)
(R)
(R)
(R)
(R)
(R)
(R)