BQ27500 Datasheet, PDF (31/39 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge

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6 APPLICATION-SPECIFIC INFORMATION
bq27500
bq27501
System-Side Impedance Track™ Fuel Gauge
SLUS785 – SEPTEMBER 2007
6.1 BATTERY PROFILE STORAGE AND SELECTION
6.1.1 General Profile Description
When a battery pack is removed from system equipment that implements the bq27500/01, the fuel gauge
will maintain some of the battery’s information in case it is re-inserted. This way, the Impedance Track™
algorithm has a means of recovering battery-status information, thereby, maintaining good
State-of-Charge (SOC) estimates.
Two default battery profiles are available to store battery information. They are used to provide the
Impedance Track™ algorithm with the default information on two possible battery types expected to be
used with the end-equipment. These default profiles can be used to support batteries of different
chemistry, same chemistry but different capacities, or same chemistry but different models. Default
profiles are programmed by the end-equipment manufacturer. Note that in the case of bq27500, only one
of the default profiles can be selected, and this selection cannot be changed during end-equipment
operation.
In addition to the default profiles, the bq27500/01 maintains two abbreviated profiles. These tables hold
dynamic battery data, and keep track of the status for up to two of the most recent batteries used. In most
cases the bq27500/01 can administrate information on two removable battery packs.
6.1.2 Activities Upon Pack Insertion
6.1.2.1 First OCV and Impedance Measurement
At power-up the BAT_GD pin is inactive, so that the system cannot obtain power from the battery (this
depends on actual implementation). In this state, the battery is put in an open-circuit condition. Next, the
bq27500/1 measures its first open-circuit voltage (OCV) via the BAT pin. From the OCV(SOC) table, the
SOC of the inserted battery is found. Then the BAT_GD pin is made active, and the impedance of the
inserted battery is calculated from the measured voltage and the load current: Z(SOC) = ( OCV(SOC) – V
) / I. This impedance is compared with the impedance of the dynamic profiles, Packn Ra, and default
profiles, Defn Ra, for the same SOC (the letter "n" depicts either a "0" or "1").
6.1.2.2 Reading Application Status
The Application Status data flash location contains cell profile status information, and can be read using
the ApplicationStatus( ) Extended Command (0x6a/0x6b). The bit configuration of this function/location is
shown in Section 6.1.3.
Application
Configuration
Byte
Table 6.1.3. ApplicationStatus( ) bit Definitions.
bit7
bit6
bit5
bit4
bit3
bit2
bit1
bit0
—
—
—
—
—
—
UNSUPBAT LU_ PROF
UNSUPBAT = Flag indicating inserted battery is not supported in the current cell profiles. True when set. bq27501 only.
LU_PROF = Last profile used by gas gauge. Cell0 last used when cleared. Cell1 last used when set. Default is 0.
6.2 APPLICATION-SPECIFIC FLOW AND CONTROL
6.2.1 Simple Battery (bq27500 Only)
The bq27500 supports only one type of battery profile. This profile is stored in both the Def0 Ra and Def1
Ra profiles. When a battery pack is inserted for the first time, the default profile is copied into the Packn
Ra profiles. Then the Impedance Track™ algorithm begins gas gauging, regularly updating Packn Ra as
the battery is used.
When an existing pack is removed from the bq27500 and a different (or same) pack is inserted, cell
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APPLICATION-SPECIFIC INFORMATION
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