STPM10 datasheet(42/47 Pages) STMICROELECTRONICS

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Application design

STPM10

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DocID17728 Rev 5

Application design

The choice of the external components in the transduction section of the application is a

crucial point in the application design, affecting the precision and the resolution of the

whole system. Among the several considerations, a compromise has to be found between

the following needs:

1. Maximize the signal to noise ratio in the voltage channel

2. Choose the current-to-voltage conversion ratio KS and the voltage divider ratio in a way

that calibration can be achieved (please refer to AN2299)

3. Choose KS to take advantage of the whole current dynamic range according to desired

maximum current and resolution. To maximize the signal to noise ratio of the current

channel the voltage divider resistors ratio should be as close as possible to those shown in

the table below

Table 15: Resistor divider ratio

Function

Component

Parameter

Value

Unit

Line voltage interface

Resistor divider

R to R ratio VRMS = 230 V

1650

V/V

R to R ratio VRMS = 110 V

830

Next figure below shows a reference schematic for an application with the following

properties:

Typical values for the current sensors sensitivity, also used in the reference schematic

below, are shown in the table below.



P = 64000 imp/kWh



INOM = 5 A



IMAX. = 60 A

Table 16: Current channel typical components

Function

Component

Parameter

Value

Unit

Line current interface

Current shunt

Current-to-voltage conversion ratio KS

0.425

mV/A

Current transformer

1.7

Rogowsky coil

0.13

If the device is used in configuration PST = 1, TMP = 1 (primary channel with CT,

secondary channel with shunt), the shunt KS must always be equal to one fourth

of the current transformer KS.

Additional considerations on the application design, suggestions for noise and crosstalk

reduction can be found in the AN2317.

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