STC3100 STMicroelectronics, STC3100 Datasheet - Page 9

• Manufacturer Part Number: STC3100
• Description: Battery monitor IC with Coulomb counter/gas gauge
• Manufacturer: STMicroelectronics

STC3100
7
7.1
Functional description
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.
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.
GND
CG
Gas gauge block diagram
AD converter
12/14-bit
cg_calibration
2
cg_enable
EOC
cg_clock
cg_res
16
32768 Hz
28
Control logic
28
accumulator
16-bit counter
28-bit
cg_rst
registers
Control
16
16
rd_req
16
Functional description
Counter
Current
register
register
Charge
register
AM00832
9/21