STC3100 Datasheet, PDF (9/21 Pages) STMicroelectronics – Battery monitor IC with Coulomb counter/gas gauge

STC3100
7
Functional description
Functional description
7.1
Gas gauge
The gas gauge is used to monitor the available battery capacity. The voltage drop across the
external sense resistor is integrated during a conversion period and input to a 12- to 14-bit
AD converter. The output conversion is accumulated into a 28-bit accumulator. The system
controller can control the gas gauge and read the data (upper 16 bits of the accumulator)
through the I2C control registers.
The AD converter output is in two’s complement format. When a conversion cycle is
completed, the result is added to the charge accumulator and the number of conversions is
incremented in a 16-bit counter.
Figure 7. Gas gauge block diagram
CG
GND
12/14-bit
AD converter
16
EOC
2 _{cg_res}
cg_clock
cg_enable
cg_calibration
16
16-bit counter
16
16
28
28-bit
accumulator
28
3
Counter
register
Current
register
Charge
register
cg_rst
rd_req
Control logic
32768 Hz
Control
registers
AM00832
The controller can read the value of the most recent conversion in two’s complement format
by reading the REG_CURRENT registers. These registers are updated at the end of each
conversion.
The differential inputs are scaled to the full range of the AD converter, introducing a small
offset error. A high value written to the CG_CAL bit of the control register connects the
inputs of the AD converter together, allowing the controller to measure the digital offset
error. Using this measurement, one can calibrate the gas gauge and reduce errors due to
the internal offset error.
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