STC3117 Datasheet, PDF (12/34 Pages) STMicroelectronics – Gas gauge IC with battery charger control for handheld applications

Functional description
STC3117
6.1.3
6.1.4
6.1.5
Internal temperature monitoring
The chip temperature (close to the battery temperature) is measured using one conversion
cycle of the A/D converter every 16 s.
The conversion cycle takes 2¹³ = 8192 clock cycles. Using the 32768 Hz internal clock, the
conversion cycle time is 250 ms. Resolution is 1° C and range is -40 to +125 °C.
The result is stored in the REG_TEMPERATURE register (see Table 11).
Current sensing in mixed mode
Current sensing is available only in mixed mode (VMODE=0).
The voltage drop across the sense resistor is integrated during a conversion period and is
input to the 14-bit sigma-delta A/D converter.
Using the 32768 Hz internal clock, the conversion cycle time is 500 ms for a 14-bit
resolution. The LSB value is 5.88 µV. The A/D converter output is in two’s complement
format.
When a conversion cycle is completed, the result is added to the Coulomb counter
accumulator and the number of conversions is incremented in a 16-bit counter.
The current register is updated after each conversion (that is: once per 500-ms
measurement cycle). The result is stored in the REG_CURRENT register (see Table 11).
Average current register
In mixed mode, an average value of the current measurement is calculated after each
current measurement with a time constant of 2 s.
The register REG_AVG_CURRENT (2 bytes) holds the average current when VMODE=0.
The LSB of REG_AVG_CURRENT is 1/4 the LSB of REG_CURRENT, that is 1.47 µV.
SOC change rate in voltage mode
Current sensing is not available in voltage mode (VMODE=1). Instead, an estimation of the
SOC change rate is provided in the REG_AVG_CURRENT register.
The SOC change rate is updated after each SOC calculation (that is: once per 4-s
measurement cycle) and is averaged with a time constant of 64 seconds. It is possible to
write an initial estimation into the REG_AVG_CURRENT register to speed-up the SOC
change rate settling time.
The REG_AVG_CURRENT register (2 bytes) holds the SOC change rate when VMODE=1.
The LSB of REG_AVG_CURRENT is 0.008789 C (by definition, 1 C means 100% SOC
change in 1 h).
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