STPM32_V02 datasheet(33/89 Pages) STMICROELECTRONICS

33 / 89 page

Parameter

Voltage

Current Shunt

Current CT

Current RoCoil

Power LSB value

LSBP=Ppulse229∙DClk= Vref2∙ 1+R1R2

kint∙AV∙AI∙kS∙calV∙calI∙228 WLSB

Energy LSB value

LSBE=Ppulse218= Vref2∙ 1+R1R2

3600∙DClk∙kint∙AV∙AI∙kS∙calV∙calI∙217 WℎLSB

1. CHVx and CHCx calibrator bits introduce in the signal processing a correction factor of ±12.5% (with an attenuation from

0.75 to 1). In order to have the maximum available up/down correction range, by default calibrator values are in the middle

of their range (0x800) corresponding to an attenuation factor calV = calI = 0.875.

2. ƩΔ bitstream should be kept lower than 0.5 (50%) to minimize modulator distortions.

3. LED_PWM is the LED frequency divider that can be set through LPWx bits in DSP_CR1 and DSP_CR2 control registers for

primary and secondary current channels respectively. Default value is 1. Please refer to Table 35

For each power register, a configurable offset value (default = 0) can be added to the instantaneous power p(n)

through OFA[9:0], OFAF[9:0], OFR[9:0], OFAS[9:0]bits in this way:

Equation 4

p′n =pn + −1OFx9∙OFx8:0 ∙22

(4)

8.4.7

RMS calculation

RMS block calculates RMS values of current and voltage on each phase continuously every 128 μs, as soon as a

new sample is available from the ADC, according to the following formulas:

Equation 5

VRMS= 1T∫t0t0+Tv2tdt

(5)

Equation 6

IRMS= 1T∫t0t0+Ti2tdt

(6)

with T = 200 ms

RMS block architecture is shown in Figure 38

Figure 38. RMS block

LPF

1/2

LPF

x2R

RMS(x)

If the cut-off frequency of an LP filter is set much below the input signal spectrum, it can be considered as an

average operator. In this case and according to the figure, the first LP filter averages its input signal which is

produced by division and multiplication:

Equation 7

STPM32, STPM33, STPM34

Functional description of hardwired DSP

DS10272 - Rev 13

page 33/89

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