BQ28Z560-R1 datasheet(32/60 Pages) TI1

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bq28z560-R1

SLUSBD3 – APRIL 2013

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FUNCTIONAL DESCRIPTION

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 m

Ω 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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