STPM10 datasheet(44/51 Pages) STMICROELECTRONICS

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Application design

STPM10

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Doc ID 17728 Rev 3

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:

Maximize the signal to noise ratio in the voltage channel,

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)

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 Table 15.

The Figure 27 below shows a reference schematic for an application with the following

properties:

●

P = 64000 imp/kWh

●

INOM = 5 A

●

IMAX = 60 A.

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

below, are shown in Table 16.

Note:

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.

Table 15.

Resistor divider ratio

Function

Component

Parameter

Value

Unit

Line voltage interface

Resistor divider

R to R ratio VRMS=230V

1650

V/V

R to R ratio VRMS=110V

830

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

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