BQ27520-G3 Datasheet, PDF (36/47 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge With Integrated LDO

bq27520-G3
SLUSAP0 – DECEMBER 2011
www.ti.com
5.8 POWER CONTROL
5.8.1 WAKE-UP COMPARATOR
The wake up comparator is used to indicate a change in cell current while the bq27520-G3 is in SLEEP
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
breached in either the charge or discharge direction. Setting both [RSNS1] and [RSNS0] to 0 disables this
feature.
Table 5-7. I_WAKE Threshold Settings⁽¹⁾
RSNS1
RSNS0
IWAKE
Vth(SRP–SRN)
0
0
0
0
0
1
0
1
0
0
1
1
1
0
0
1
0
1
1
1
0
1
1
1
Disabled
Disabled
1.0 mV or –1.0 mV
2.2 mV or –2.2 mV
2.2 mV or –2.2 mV
4.6 mV or –4.6 mV
4.6 mV or –4.6 mV
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. The voltage 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 bq27520-G3 V_CC voltage does not fall below its minimum of 2.4 V during Flash write operations.
5.9 AUTOCALIBRATION
The bq27520-G3 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; hence, the offset calibration is aborted.
36
FUNCTIONAL DESCRIPTION
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