BQ28Z560-R1_14 Datasheet, PDF (32/61 Pages) Texas Instruments – Single Cell Li-Ion Battery Gas Gauge

bq28z560-R1
Not Recommended For New Designs
SLUSBD3 – APRIL 2013
FUNCTIONAL DESCRIPTION
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FUEL GAUGING
The bq28z560-R1 measures the cell voltage, temperature, and current to determine the battery SOC based on
the Impedance Track algorithm (refer to the Theory and Implementation of Impedance Track Battery Fuel-
Gauging Algorithm Application Report [SLUA450] for more information). The bq28z560-R1 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 battery’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 values are taken from a cell manufacturers' data sheet multiplied by the number of
parallel cells. It is also used for the value in Design Capacity. The bq28z560-R1 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 Terminate Voltage. NominalAvailableCapacity() and FullAvailableCapacity()
are the uncompensated (no or light load) versions of RemainingCapacity() and FullChargeCapacity(),
respectively.
The bq28z560-R1 has two flags accessed by the Flags() function that warn 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 bq28z560-R1 has two additional flags accessed by the Flags() function that warn of internal battery
conditions. The gas 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 bq28z560-R1 also has the capability to
detect when a tab is disconnected in a 2-cell parallel system by actively monitoring the SOH. When this
conditions occurs, [TDD] will be set.
IMPEDANCE TRACK VARIABLES
The bq28z560-R1 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 mode or CONSTANT POWER mode for the
Impedance Track algorithm as used in Load Select (see Load Select). When LOAD mode is 0, the CONSTANT
CURRENT mode is used (default). When LOAD mode is 1, CONSTANT POWER mode 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 mode 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 11 are
available.
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