STPM32TR datasheet(52/121 Pages) STMICROELECTRONICS

52 / 121 page

Theory of operation

STPM32, STPM33, STPM34

52/121

DS10272 Rev 8

With an AC input signal:

Equation 10

The LP filter cuts the 2nd harmonic component of input signal multiplying it by a dumping

factor α:

Equation 11

R result is a DC signal plus the 2nd harmonic ripple with the amplitude of α/2.

For dumping factor | α |<<1:

Equation 12

RMS updated values are available in DSP_REG14 and DSP_REG15 registers every

128 μs.

Raw ADC samples are also available for post-processing by MCU in registers from

DSP_REG2 to DSP_REG9.

By taking into account the internal parameters in Table 13 and the analog front end

components in Table 14, LSB values of voltage and current registers are the following:

Table 15. STPM3x current voltage LSB values

Parameter

Value

Voltage RMS LSB value

Current RMS LSB value

Instantaneous voltage normalized

RA 1 

t



cos

–

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

------- 1 

---

t



cos

–







-------



LSBVRMS

Vref 1R1 R2







calV AV 2



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



LSBIRMS

Vref

calI AI 2

17 k

 S kint





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



 V

norm



–

 2

23 vn

 23

 vn

 22:0





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

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