BQ27520-G2 Datasheet, PDF (36/47 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge With Integrated LDO

bq27520-G2
SLUSAB7A – MARCH 2011 – REVISED AUGUST 2011
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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 bq27520-G2 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 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
Configuration
Byte
—
—
—
—
—
—
—
LU_PROF = Last profile used by fuel gauge. Cell0 last used when cleared. Cell1 last used when set. Default is 0.
bit0
LU_ PROF
6.2 APPLICATION-SPECIFIC FLOW AND CONTROL
The bq27520-G2 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 gas gauging, regularly updating Packn as the
battery is used.
When an existing pack is removed from the bq27520-G2 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
Impedance Measurement). The bq27520-G2 chooses the profile which is closest to the measured
impedance, starting with the Packn profiles. That is, if the measured impedance matches Pack0, then the
Pack0 profile is used. If the measured impedance matches Pack1, then the Pack1 profile is used. If the
measured impedance does not match the impedance stored in either Pack0 or Pack1, the battery pack is
deemed new (none of the previously used packs). Either Def0/Def1 profile is copied into either the Pack0
or Pack1 profile, overwriting the oldest Packn profile.
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APPLICATION-SPECIFIC INFORMATION
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