BQ34Z100 Datasheet, PDF (16/50 Pages) Texas Instruments – Wide Range Fuel Gauge with Impedance Track™ Technology

bq34z100
SLUSAU1 – MAY 2012
FUNCTIONAL DESCRIPTION
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FUEL GAUGING
The bq34z100 measures the cell voltage, temperature, and current to determine the battery SOC based in the
Impedance Track algorithm (refer to Theory and Implementation of Impedance Track Battery Fuel-Gauging
Algorithm Application Report [SLUA450] for more information). The bq34z100 monitors charge and discharge
activity by sensing the voltage across a small-value resistor (5 mΩ to 20 mΩ typ.) between the SRP and SRN
pins and in-series with the cell. By integrating charge passing through the battery, the cell’s SOC is adjusted
during battery charge or discharge.
The total battery capacity is found by comparing states of charge before and after applying the load with the
amount of charge passed. When an application load is applied, the impedance of the cell is measured by
comparing the OCV obtained from a predefined function for present SOC with the measured voltage under load.
Measurements of OCV and charge integration determine chemical state of charge and Chemical Capacity
(Qmax). The initial Qmax value is taken from a cell manufacturers' data sheet multiplied by the number of parallel
cells. The parallel value is also used for the value programmed in Design Capacity. The bq34z100 acquires and
updates the battery-impedance profile during normal battery usage. It uses this profile, along with SOC and the
Qmax value, to determine FullChargeCapacity() and StateOfCharge(), specifically for the present load and
temperature. FullChargeCapacity() is reported as capacity available from a fully charged battery under the
present load and temperature until Voltage() reaches the Terminate Voltage. NominalAvailableCapacity() and
FullAvailableCapacity() are the uncompensated (no or light load) versions of RemainingCapacity() and
FullChargeCapacity(), respectively.
The bq34z100 has two flags accessed by the Flags() function that warns when the battery’s SOC has fallen to
critical levels. When RemainingCapacity() falls below the first capacity threshold, specified in SOC1 Set
Threshold, the [SOC1] (State of Charge Initial) flag is set. The flag is cleared once RemainingCapacity() rises
above SOC1 Clear Threshold. All units are in mAh.
When RemainingCapacity() falls below the second capacity threshold, SOCF Set Threshold, the [SOCF] (State
of Charge Final) flag is set, serving as a final discharge warning. If SOCF Set Threshold = –1, the flag is
inoperative during discharge. Similarly, when RemainingCapacity() rises above SOCF Clear Threshold and the
[SOCF] flag has already been set, the [SOCF] flag is cleared. All units are in mAh.
The bq34z100 has two additional flags accessed by the Flags() function that warn of internal battery conditions.
The fuel gauge monitors the cell voltage during relaxed conditions to determine if an internal short has been
detected When this condition occurs, [ISD] will be set. The bq34z100 also has the capability of detecting when a
tab has been disconnected in a 2-cell parallel system by actively monitoring the state of health. When this
condition occurs, [TDD] will be set.
IMPEDANCE TRACK VARIABLES
The bq34z100 has several data flash variables that permit the user to customize the Impedance Track algorithm
for optimized performance. These variables are dependent upon the power characteristics of the application as
well as the cell itself.
Load Mode
Load Mode is used to select either the constant current or constant power model for the Impedance Track
algorithm as used in Load Select. See the Load Select section. When Load Mode is 0, the Constant Current
Model is used (default). When Load Mode is 1, the Constant Power Model is used. The [LDMD] bit of
CONTROL_STATUS reflects the status of Load Mode.
Load Select
Load Select defines the type of power or current model to be used to compute load-compensated capacity in the
Impedance Track algorithm. If Load Mode = 0 (Constant Current) then the options presented in Table 8 are
available.
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