ST ST7538Q, Примечание к применению

Страница: 29 / 56

AN2744 Board description
29/56
5.1.5 Input impedance
The input impedance of a power line communication node is another critical point. Figure 22
through 25 show the curves of input impedance magnitude vs. frequency in both Tx and Rx
mode for the two channels.
The impedance magnitude values prove that the ST7538Q dual channel reference design
board is compliant with EN50065-7 normative, which sets the following minimum impedance
constraints for this kind of equipment:
– Tx mode: free in the range 3 to 95 kHz, 3
Ω
from 95 to 148.5 kHz
– Rx mode: 10
Ω
from 3 to 9 kHz, 50
Ω
between 9 and 95 kHz only inside signal 20 dB-
bandwidth (free for frequencies outside signal bandwidth), 5
Ω
from 95 to 148.5 kHz
Figure 21. Simulated frequency response of the Rx active filter for 86 kHz channel with tolerance
effect
4E4 5E4 6E4 7E4 8E4 9E4 1E5 2E5 3E4 3E5
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
8
9
10
11
-8
12
2 dB
4E4 5E4 6E4 7E4 8E4 9E4 1E5 2E5 3E4 3E5
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
8
9
10
11
-8
12
2 dB
Figure 22. Measured input impedance magnitude of the coupling interface in Rx mode for the 72
kHz channel (typical curve)
1
10
100
1000
1E+04 1E+05 1E+06
Freq (Hz)
Impedance
mod
u
lu
s (
Ω
)
EN50065 EN50065 - - 7 7
1
10
100
1000
1E+04 1E+05 1E+06
Freq (Hz)
Impedance
mod
u
lu
s (
Ω
)
1
10
100
1000
1E+04 1E+05 1E+06
Freq (Hz)
Impedance
mod
u
lu
s (
Ω
)
EN50065 EN50065 - - 7 7