BQ27520-G2 Datasheet, PDF (25/47 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge With Integrated LDO

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bq27520-G2
SLUSAB7A – MARCH 2011 – REVISED AUGUST 2011
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 bq27520-G2 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 Set Threshold. The bq27520-G2’s BAT_LOW pin automatically
reflects the status of the [SOC1] flag. This flag is enabled when BL_INT bit in Operation Configuration B
is set. All units are in mAh.
When Voltage( ) falls below the system shut down threshold voltage, SysDown Set Volt Threshold, the
[SYSDOWN] flag is set, serving as a final warning to shut down the system. The SOC_INT also signals.
When Voltage( ) rises above SysDown Clear Voltage and the [SYSDOWN] flag has already been set,
the [SYSDOWN] flag is cleared. The SOC_INT also signals such change. All units are in mV.
When the voltage is discharged to Final Voltage, the SOC will be set as 0.
5.2 IMPEDANCE TRACK™ VARIABLES
The bq27520-G2 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.
5.2.1 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 Load Select). When Load Mode is 0, the Constant
Current Model is used (default). When 1, the Constant Power Model is used. The [LDMD] bit of
CONTROL_STATUS reflects the status of Load Mode.
5.2.2 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 5-1 are available.
Table 5-1. Constant-Current Model Used When Load Mode = 0
LoadSelect Value
0
1(default)
2
3
4
5
6
Current Model Used
Average discharge current from previous cycle: There is an internal register that records the average discharge
current through each entire discharge cycle. The previous average is stored in this register.
Present average discharge current: This is the average discharge current from the beginning of this discharge cycle
until present time.
Average current: based on AverageCurrent( )
Current: based off of a low-pass-filtered version of AverageCurrent( ) (τ =14 s)
Design capacity / 5: C Rate based off of Design Capacity /5 or a C/5 rate in mA.
AtRate (mA): Use whatever current is in AtRate( )
User_Rate-mA: Use the value in User_Rate-mA. This mode provides a completely user-configurable method.
If Load Mode = 1 (Constant Power) then the following options shown in Table 5-2 are available
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FUNCTIONAL DESCRIPTION
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