BQ27742-G1 Datasheet, PDF (23/46 Pages) Texas Instruments – Single-Cell Li-Ion Battery Fuel Gauge with Programmable Hardware Protection

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bq27742-G1
SLUSBV9C – MARCH 2014 – REVISED FEBRUARY 2016
Device Functional Modes (continued)
7.4.3 OVERTEMPERATURE FAULT Mode
Gauging firmware monitors temperature every second and will open either the CHG FET if Temperature() > OT
Chg for OT Chg Time in CHARGING mode or open the DSG FET if Temperature() > OT Dsg for OT Dsg Time
in DISCHARGING mode. Gauge determination of charge or discharge mode is based on Current() > Chg
Current Threshold for Quit Relax Time or Current() < Dsg Current Threshold for Quit Relax Time. Recovery
from the given overtemperature fault occurs when Temperature() < OT Chg Recovery or < OT Dsg Recovery,
depending on if a charge overtemperature or discharge overtemperature fault is present.
7.4.4 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 7. An internal event is
generated when the threshold is breached in either charge or discharge directions.
Table 7. 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.
7.5 Battery Parameter Measurements
7.5.1 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.
7.5.2 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.
7.5.3 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.
7.5.4 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.
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