STPMC1 datasheet(31/77 Pages) STMICROELECTRONICS

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STPMC1

Theory of operation

Doc ID 15728 Rev 6

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Example 6: 3-ph system - BCS = 1

Let us consider a three-phase, four wires system where:

IR = 5 A

IS = 5 A

IT = 3.2 A

IN = 0 A

The tamper is evaluated because

IR + IS +IT +IN = 13.2 A > 0,703125 A = IMAX / 256

In this case

sIRMS = 0,449901 A > 0,4125 A = (IR + IS +IT +IN) / 32

Then BCS = 1.

Example 7: 1-ph system - BCS = 0

Let us consider a single phase systems with only S and T wires connected where

IS= 5 A

IT = 4 A

IMAX = 180 A

In this case the criterion for tamper evaluation is verified since:

(IS + IT) = 9 A > 0,703125 A = IMAX / 256

But BCS = 0 because

7/9 IT = 3.11 A < IS = 5 A < 9/7 IT = 5.14 A

and

7/9 IS = 3.88 A < IT = 4 A < 9/7 IS = 6.43 A

Example 8: 1-ph system - BCS = 1

Let us consider the case in which:

IS = 5 A

IT = 3 A

IMAX = 180 A

Also in this case the criterion for tamper evaluation is verified:

(IS + IT) = 8 A > 0,703125 A = IMAX / 256

Now BCS = 1 because

7/9 IS = 3.88 A > IT = 3 A

9.10.2

Phase sequence is wrong (status bit

BSF)

One tamper condition is that phase sequence is not correct. A 3-ph phase status bit

BSF

checks the sequence of phases, which, in a three phase system is one of the following:

●

→ S → T

●

→ T → R

●

→ R → S

In one of the above cases

BSF is cleared, otherwise bit BSF is set.

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