BQ27742-G1 Datasheet, PDF (33/46 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
Typical Applications (continued)
NAME
Prot OV Config
Prot Checksum
CC Gain
CC Delta
CC Offset
Board Offset
Pack V Offset
Table 11. Key Data Flash Parameters for Configuration (continued)
DEFAULT
07
11
5
5.074
6.874
0.66
0
UNIT
hex
hex
mΩ
mΩ
mA
uA
mV
RECOMMENDED SETTING
Set to maximum tolerable cell voltage before cell is permanently damaged.
Serves as a second level OVP protection mechanism.
Set to sum of Prot OC Config and Prot OV Config. Improper setting will cause
FETs to open and warning flag assertion in SafetyStatus(), until corrected.
Calibrate this parameter using TI-supplied BMS software and calibration
procedure in the TRM. Determines conversion of coulomb counter measured
sense resistor voltage to current.
Calibrate this parameter using TI-supplied BMS software and calibration
procedure in the TRM. Determines conversion of coulomb counter measured
sense resistor voltage to passed charge.
Calibrate this parameter using TI-supplied BMS software and calibration
procedure in the TRM. Determines native offset of coulomb counter hardware
that should be removed from conversions.
Calibrate this parameter using TI-supplied BMS software and calibration
procedure in the TRM. Determines native offset of the printed circuit board
parasitics that should be removed from conversions.
Calibrate this parameter using TI-supplied BMS software and calibration
procedure in the TRM. Determines voltage offset between cell tab and ADC input
node to incorporate back into or remove from measurement, depending on
polarity.
8.2.3 Detailed Design Procedure
8.2.3.1 BAT Voltage Sense Input
A ceramic capacitor at the input to the BAT pin is used to bypass AC voltage ripple to ground, greatly reducing
its influence on battery voltage measurements. It proves most effective in applications with load profiles that
exhibit high frequency current pulses (that is, cell phones) but is recommended for use in all applications to
reduce noise on this sensitive high impedance measurement node.
The series resistor between the battery and the BAT input is used to limit current that could be conducted
through the chip-scale package's solder bumps in the event of an accidental short during the board assembly
process. The resistor is not likely to survive a sustained short condition (depends on power rating), however, it
sacrifices the much cheaper resistor component over suffering damage to the fuel gauge die itself.
8.2.3.2 SRP and SRN Current Sense Inputs
The filter network at the input to the coulomb counter is intended to improve differential mode rejection of voltage
measured across the sense resistor. These components should be placed as close as possible to the coulomb
counter inputs and the routing of the differential traces length-matched in order to best minimize impedance
mismatch-induced measurement errors. The single-ended ceramic capacitors should be tied to the battery
voltage node (preferably to a large copper pour connected to the SRN side of the sense resistor) in order to
further improve common-mode noise rejection. The series resistors between the CC inputs and the sense
resistor should be at least 200 Ω in order to mitigate SCR-induced latch-up due to possible ESD events.
8.2.3.3 Sense Resistor Selection
Any variation encountered in the resistance present between the SRP and SRN pins of the fuel gauge will affect
the resulting differential voltage, and derived current, it senses. As such, it is recommended to select a sense
resistor with minimal tolerance and temperature coefficient of resistance (TCR) characteristics. The standard
recommendation based on best compromise between performance and price is a 1% tolerance, 50-ppm drift
sense resistor with a 1-W power rating.
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