BQ27620-G1 Datasheet, PDF (36/45 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge

bq27620-G1
SLUSAE3 – OCTOBER 2012
6 APPLICATION-SPECIFIC INFORMATION
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6.1 BATTERY PROFILE STORAGE AND SELECTION
6.1.1 Common Profile Aspects
The bq27620-G1 maintains two chemistry profiles, PACK0 and PACK1. These profiles hold dynamic
battery data, and keep track of the status for up to two of the most recent batteries used. When a battery
pack is removed from host equipment, the bq27620-G1 selects the battery information when the battery is
re-inserted. This way, Impedance Track™ algorithm has a means of recovering battery-status information,
thereby maintaining good state-of-charge (SOC) estimates.
The bq27620-G1 can manage the information on two removable battery packs. In addition, the gauge has
two default battery profiles available to store battery information. The profiles 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. If a new pack is inserted that replaces an older worn out pack, the gauge
automatically selects from one of the default profiles and writes that data into the oldest of the PACK0 or
PACK1 profile.
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 might not obtain power from the battery (this
depends on actual implementation). In this state, the battery should be put in a condition with load current
less than C/20. Next, the bq27620-G1 measures its first open-circuit voltage (OCV) via the BAT pin. The
[OCVCMDCOMP] bit will set once the OCV measurement is completed. Depending on the load current,
the [OCVFAIL] bit indicates whether the OCV reading is valid. 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).The [INITCOMP] bit will be set afterwards and the
OCV command could be issued
6.1.3 Reading HostCfg
The HostCfg 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. HostCfg Bit Definitions.
HostCfg
bit7
bit6
bit5
bit4
bit3
bit2
bit1
Byte
—
—
—
—
OPTCMP
—
—
LU_PROF = Last profile used by fuel gauge. Cell0 last used when cleared. Cell1 last used when set. Default is 0.
OPTCMP = OPTMIZ bit is set. Default is 0.
bit0
LU_ PROF
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APPLICATION-SPECIFIC INFORMATION
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