STPMC1 datasheet(29/77 Pages) STMICROELECTRONICS

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STPMC1

Theory of operation

Doc ID 15728 Rev 6

29/77

Where:

Imax = 2

Σ IX = IR + IS + IT + IN

for SYS = 0, 1, 2, 3, 4, 7

Σ IX = IS + IT

for SYS = 5, 6

Bit

BCS is set according to Table 15

with (

Σ iX)RMS = (iR + iS + iT + iN)RMS

Example 5: 3-ph system - BCS = 0

Let us consider a three-phase, four wires system where the RMS values of the current

applied are:

IR = 5 A

IS = 5 A

IT = 4.4 A

IN = 0 A

The sum of all instantaneous currents (iR + iS + iT + iN) should always be zero, unless

there is a tamper condition.

The STPMC1 calculates this sum and put its RMS value divided by four (called sIRMS)

into register DMN (see paragraph

9.17.2).

This value should always be zero (or very close).

In our case:

The currents are shown in

Figure 11 below.

∑ >

256

max

Table 15.

Tamper conditions

BCS

SYS = 0, 1, 2, 3, 4, 7

SYS = 5, 6

()

RMS

∑

()

RMS

∑

149967

sIRMS

RMS

⎟

⎠

⎞

⎜

⎝

⎛

∑

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