BQ27741-G1_14 Datasheet, PDF (16/39 Pages) Texas Instruments – Single Cell Li-Ion Battery Fuel Gauge with Integrated Protection

bq27741-G1
SLUSBF2 – JULY 2013
www.ti.com
Wake-Up Comparator
The wake-up comparator indicates a change in cell current while the fuel gauge is in SLEEP mode. Wake
comparator threshold can be configured in firmware and set to the thresholds in Table 3. An internal event is
generated when the threshold is breached in either charge or discharge directions.
Table 3. I_WAKE Threshold Settings⁽¹⁾
RSNS1
RSNS0
IWAKE
Vth(SRP-SRN)
0
0
0
Disabled
0
0
1
Disabled
0
1
0
1.0 mV or –1.0 mV
0
1
1
2.2 mV or –2.2 mV
1
0
0
2.2 mV or –2.2 mV
1
0
1
4.6 mV or –4.6 mV
1
1
0
4.6 mV or –4.6 mV
1
1
1
9.8 mV or –9.8 mV
(1) The actual resistance value versus 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.
Battery Parameter Measurements
Charge and Discharge Counting
The integrating delta-sigma ADC measures the charge or discharge flow of the battery by measuring the voltage
drop across a small-value sense resistor between the SRP and SRN pins. The integrating ADC measures bipolar
signals and detects charge activity when V_SR = V_SRP – V_SRN is positive and discharge activity when V_SR = V_SRP –
V_SRN is negative. The fuel gauge continuously integrates the signal over time using an internal counter.
Voltage
The fuel gauge updates cell voltages at 1-second intervals when in NORMAL mode. The internal ADC of the fuel
gauge measures the voltage, and scales and calibrates it appropriately. Voltage measurement is automatically
compensated based on temperature. This data is also used to calculate the impedance of the cell for Impedance
Track™ fuel gauging.
Current
The fuel gauge uses the SRP and SRN inputs to measure and calculate the battery charge and discharge
current using a 5-mΩ to 20-mΩ typical sense resistor.
Auto-Calibration
The fuel gauge provides an auto-calibration feature to cancel the voltage offset error across SRN and SRP for
maximum charge measurement accuracy. The fuel gauge performs auto-calibration before entering the SLEEP
mode.
Temperature
The fuel gauge external temperature sensing is optimized with the use of a high-accuracy negative temperature
coefficient (NTC) thermistor with R25 = 10 kΩ ± 1% and B25/85 = 3435 kΩ ± 1% (such as Semitec 103AT for
measurement). The fuel gauge can also be configured to use its internal temperature sensor. The fuel gauge
uses temperature to monitor the battery-pack environment, which is used for fuel gauging and cell protection
functionality.
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