STPM32 datasheet(61/121 Pages) STMICROELECTRONICS

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DS10272 Rev 8

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STPM32, STPM33, STPM34

Theory of operation

121

Tamper circuit works if energies associated with the two current channels are both positive

or negative, if two energies have different sign, a warning flag “TAMPER OR WRONG” in

DSP_SR1 or DSP_SR2 is set.

The channel with higher energy is signaled by PHx TAMPER status bit in DSP_SR1 or

DSP_SR2.

When internal signals are not good enough to perform the calculations, for example line

period is out or range or sigma-delta signals from analog section are stuck at high or low

logic level, the tamper module is disabled and its state is set to normal.

8.4.12

AH accumulation

In this particular tamper, the neutral wire is disconnected from the meter and the STPM3x

does not sense the voltage anymore, while it keeps sensing the current information. In these

conditions, AH accumulator can be used by the microcontroller to regularly calculate the

billing based on a nominal voltage value due to the following equation:

Equation 18

Energy = AH_ACC[31:0]·LSBAH_ACC·VNOM [Wh]

If voltage is too low (sag event detected) or period is wrong (PER_ERR = 1) and RMS value

of current is high enough, RMS current is accumulated in the register AH_ACC[31:0]. Value

in PHx AH_ACC[31:0] register is increased with a DCLK frequency.

Figure 45. AH accumulation block

The accumulation of current values is controlled by AH status bit. AH bit is set when

PER_ERR = 1 and real values of current overcome an upper threshold set in AH_UPx[11:0]

in DSP_CR9 and DSP_CR11. This bit is cleared when RMS current drops below

AH_DOWNx[11:0] threshold in DSP_CR10 and DSP_CR12.

To stabilize the current accumulation, SAG event should be monitored by setting some

thresholds in the related register.

STPM32 Datasheet(PDF) 61 Page - STMicroelectronics