Datasheet

Application design STPM10
46/53 Doc ID 17728 Rev 4
8 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 Ta bl e 15.
The Figure 27 below shows a reference schematic for an application with the following
properties:
● P = 64000 imp/kWh
● I
NOM
= 5 A
● I
MAX
= 60 A.
Typical values for the current sensors sensitivity, also used in the reference schematic
below, are shown in Tabl e 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 V
RMS
=230V 1650
V/V
R to R ratio V
RMS
=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/ACurrent transformer 1.7
Rogowsky coil 0.13