Functional description

STC3117

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DocID025792 Rev 2

6.1.3

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.

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).

6.1.4

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.

6.1.5

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).