BQ27541 Datasheet, PDF (29/38 Pages) Texas Instruments – Single Cell Li-Ion Battery Fuel Gauge for Battery Pack Integration

bq27541
www.ti.com ........................................................................................................................................................................................... SLUS861 – DECEMBER 2008
Wake-Up Comparator
The wake up comparator is used to indicate a change in cell current while the bq27541 is in either SLEEP or
HIBERNATE modes. Pack 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 11. 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.
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 bq27541
Vcc voltage does not fall below its minimum of 2.4V during Flash write operations.
AUTOCALIBRATION
The bq27541 provides an autocalibration feature that will measure the voltage offset error across SRP and SRN
from time-to-time as operating conditions change. It subtracts the resulting offset error from normal sense
resistor voltage, V_SR, for maximum measurement accuracy.
Autocalibration 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.
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): bq27541
Submit Documentation Feedback
29