STPM32 datasheet(50/121 Pages) STMICROELECTRONICS

50 / 121 page

Theory of operation

STPM32, STPM33, STPM34

50/121

DS10272 Rev 8

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

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

Equation 6

with T = 200 ms.

Power LSB value

Energy LSB value

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 36 on page 81.

Table 14. STPM3x basic calculations (continued)

Parameter

Voltage

Current shunt

Current CT

Current Rogowski coil

LSBP

Ppulse

---------------- DClk

Vref

1R1 R2







kint AV AI kS calV calI 2





------------------------------------------------------------------------------------- W

LSB

------------



LSBE

Ppulse

----------------

Vref

1R1 R2







3600 DClk kint AV AI kS calV calI 2





--------------------------------------------------------------------------------------------------------------------------

LSB

------------

 n



–



OFx 9

 OFx 8:0

 2





VRMS

---



2 t

t0 T



IRMS

---



2 t

t0 T



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