BQ27500-V120 Datasheet, PDF (28/36 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge

bq27500-V120
System-Side Impedance Track™ Fuel Gauge
SLUS880 – OCTOBER 2008
www.ti.com
5.8 POWER CONTROL
5.8.1 RESET FUNCTIONS
When the bq27500 detects software reset ([RESET] bit of Control( ) initiated), it increments the
corresponding counter. This information is accessible by issuing the command Control( ) function with the
RESET_DATA subcommand.
5.8.2 WAKE-UP COMPARATOR
The wake up comparator is used to indicate a change in cell current while the bq27500 is in either SLEEP
or HIBERNATE mode. Operation Configuration uses bits [RSNS1–RSNS0] to set the sense resistor
selection. Operation Configuration also uses the [IWAKE] bit to select one of two possible voltage
threshold ranges for the given sense resistor selection. An internal interrupt is generated when the
threshold is reached in either the charge or discharge direction. Setting both [RSNS1] and [RSNS0] to 0
disables this feature.
RSNS1
0
0
0
0
1
1
1
1
Table 5-4. I_WAKE Threshold Settings⁽¹⁾
RSNS0
IWAKE
Vth(SRP–SRN)
0
0
Disabled
0
1
Disabled
1
0
1.0 mV or –1.0 mV
1
1
2.2 mV or –2.2 mV
0
0
2.2 mV or –2.2 mV
0
1
4.6 mV or –4.6 mV
1
0
4.6 mV or –4.6 mV
1
1
9.8 mV or –9.8 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.
5.8.3 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 bq27500 V_CC voltage does not fall below its minimum of 2.4 V during Flash write operations.
5.9 AUTOCALIBRATION
The bq27500 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 8°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 considerably; hence, the offset calibration is aborted.
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FUNCTIONAL DESCRIPTION
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