BQ27541-V200_1007 Datasheet, PDF (31/43 Pages) Texas Instruments – Single Cell Li-Ion Battery Fuel Gauge for Battery Pack Integration

bq27541-V200
www.ti.com
SLUSA11 – FEBRUARY 2010
mode, because any changes in battery charge status will not be measured. If necessary, the host equipment can
draw a small current (generally infrequent and less than 1mA, for purposes of low-level monitoring and updating);
however, the corresponding charge drawn from the battery will not be logged by the gauge. Once the gauge
exits to NORMAL mode, the IT algorithm will take about 3 seconds to re-establish the correct battery capacity
and measurements, regardless of the total charge drawn in HIBERNATE mode. During this period of
re-establishment, the gauge reports previously calculated values prior to entering HIBERNATE mode. The host
can identify exit from HIBERNATE mode by checking if Voltage() < Hibernate Voltage or [HIBERNATE] bit is
cleared by the gauge.
If a charger is attached, the host should immediately take the fuel gauge out of HIBERNATE mode before
beginning to charge the battery. Charging the battery in HIBERNATE mode will result in a notable gauging error
that will take several hours to correct.
POWER CONTROL
Reset Functions
When the bq27541 detects a software reset ([RESET] bit of Control( ) initiated), it determines the type of reset
and increments the corresponding counter. This information is accessible by issuing the command Control( )
function with the RESET_DATA subcommand.
Wake-Up Comparator
The wake up comparator is used to indicate a change in cell current while the bq27541 is in SLEEP 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 13. 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. The voltage thresholds are typical values under room
temperature.
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.
Copyright © 2010, Texas Instruments Incorporated
Product Folder Link(s): bq27541-V200
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