Converting readings into measured values

AN3254

18/24

Doc ID 17783 Rev 1

The interrupt service should do the following:

●

update

e

●

generate output pulses (if needed) from

e

●

call the next subtask

●

perform other tasks (if needed)

In this way the addition of

e

output pulse that has a 16 times better accuracy of position in time, which would reduce the

jitter of an eventual LED output.

5.2

Other values

5.2.1

Voltage, current, and frequency calculation

The ratio between the register value and the actual voltage, current, or frequency value is a

function of the voltage and current sensor sensitivity and of the device internal parameters,

like analog amplification, reference voltage, measurement frequency, calibrator, attenuation

of each stage of decimation filter, and power meter constant.

Formulas to convert the readings into meaningful values are reported below.

For details on the device configuration bits mentioned below, please refer to the STPMC1

datasheet.

In any case, as the internal parameter values, here given as constants, are subject to

process drift, and the sensors sensitivity are subject to tolerance, even if these fluctuations

are compensated by the calibrators, the best way to obtain the proper parameters is to

measure known signals and calculate the ratio between the register value and actual value.

The device linearity ensures that the ratio remains constant.

Figure 8, 9, and 10 below show the signal processing chains for each phase current and

voltage.

Figure 8.

Voltage signal path