BQ27500_08 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
SLUS785D – SEPTEMBER 2007 – REVISED APRIL 2008
6.1 BATTERY PROFILE STORAGE AND SELECTION
6.1.1 Common Profile Aspects
When a battery pack is removed from host equipment that implements the bq27500/01, the fuel gauge
maintains some of the battery information in case the battery 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 manage the 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 host cannot obtain power from the battery (this
depends on the 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, and the default
profiles, Defn, for the same SOC (the letter n depicts either a 0 or 1).
6.1.3 Reading Application Status
The Application Status data flash location contains cell profile status information, and can be read using
the ApplicationStatus( ) extended command (0x6a). The bit configuration of this function/location is shown
in Table 6-1.
Table 6-1. ApplicationStatus( ) Bit Definitions.
Application
bit7
bit6
bit5
bit4
bit3
bit2
bit1
bit0
Configuration
Byte
—
—
—
—
—
—
UNSUPBAT LU_ PROF
UNSUPBAT = Flag indicating inserted battery is not supported in the current cell profiles. bq27501 only. True when set. Default is 0.
LU_PROF = Last profile used by fuel gauge. Pack0 last used when cleared. Pack1 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 and Def1
profiles. When a battery pack is inserted for the first time, the default profile is copied into the Packn
profiles. Then the Impedance Track™ algorithm begins fuel gauging, regularly updating Packn as the
battery is used.
When an existing pack is removed from the bq27500 and a different (or same) pack is inserted, cell
impedance is measured immediately after battery detection (see Section 6.1.2.1, First OCV and
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APPLICATION-SPECIFIC INFORMATION
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