BQ27505 Datasheet, PDF (33/42 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge

Not Recommended for New Designs
bq27505
www.ti.com
SLUS884 – FEBRUARY 2009
Table 5-6. I_WAKE Threshold Settings⁽¹⁾
RSNS1
0
0
0
0
1
1
1
1
RSNS0
0
0
1
1
0
0
1
1
IWAKE
0
1
0
1
0
1
0
1
Vth(SRP–SRN)
Disabled
Disabled
1.25 mV or –1.25 mV
2.5 mV or –2.5 mV
2.5 mV or –2.5 mV
5 mV or –5 mV
5 mV or –5 mV
10 mV or –10 mV
(1) The actual resistance value vs the setting of the sense resistor is not important, just the actual voltage
threshold when calculating the configuration. The votage thresholds are typical values under room
temperature.
5.8.2 FLASH UPDATES
Data Flash can only be updated if Voltage( ) ≥ Flash Update OK Voltage. Flash programming current can
cause an increase in LDO dropout. The value of Flash Update OK Voltage should be selected such that
the bq27505 V_CC voltage does not fall below its minimum of 2.4 V during Flash write operations.
5.9 AUTOCALIBRATION
The bq27505 provides an autocalibration feature that measures the voltage offset error across SRP and
SRN as operating conditions change. It subtracts the resulting offset error from normal sense resistor
voltage, V_SR, for maximum measurement accuracy.
Autocalibration of the coulomb counter begins on entry to SLEEP mode, except if Temperature( ) is ≤ 5°C
or Temperature( ) ≥ 45°C.
The fuel gauge also performs a single offset when (1) the condition of AverageCurrent( ) ≤ 100 mA and (2)
{voltage change since last offset calibration ≥ 256 mV} or {temperature change since last offset calibration
is greater than 80°C for ≥ 60 s}.
Capacity and current measurements continue at the last measured rate during the offset calibration when
these measurements cannot be performed. If the battery voltage drops more than 32 mV during the offset
calibration, the load current has likely increased; hence, the offset calibration is aborted.
6 APPLICATION-SPECIFIC INFORMATION
6.1 BATTERY PROFILE STORAGE AND SELECTION
6.1.1 Common Profile Aspects
When a battery pack is removed from system equipment that implements the bq27505, the fuel gauge will
maintain some of the battery information, if it is re-inserted. This way the Impedance Track™ algorithm will
often have 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. 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 bq27505 maintains two abbreviated profiles: Cell0 and Cell1. 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 bq27505 can administrate information on two removable battery packs.
Copyright © 2009, Texas Instruments Incorporated
APPLICATION-SPECIFIC INFORMATION
33
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