BQ27500 Datasheet, PDF (30/39 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge

bq27500
bq27501
System-Side Impedance Track™ Fuel Gauge
SLUS785 – SEPTEMBER 2007
www.ti.com
5.8.2 WAKE-UP COMPARATOR
The wake up comparator is used to indicate a change in cell current while the bq27500/1 is in either
SLEEP or HIBERNATE modes. 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 breached in either charge or discharge directions. 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
1.25 mV or –1.25 mV
1
1
2.5 mV or –2.5 mV
0
0
2.5 mV or –2.5 mV
0
1
5 mV or –5 mV
1
0
5 mV or –5 mV
1
1
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.
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 bq27500/1 V_CC voltage does not fall below its minimum of 2.4V 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.
Auto calibration of the ADC 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( ) ≤ 100mA and (2)
{voltage change since last offset calibration ≥ 256mV} or {temperature change since last offset calibration
is greater than 80°C for ≥ 60s}.
Capacity and current measurements will continue at the last measured rate during the offset calibration
when these measurements cannot be performed. If the battery voltage drops more than 32mV during the
offset calibration, the load current has likely increased considerably; hence, the offset calibration will be
aborted.
30
FUNCTIONAL DESCRIPTION
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