ADM488 Analog Devices, ADM488 Datasheet - Page 10

• Manufacturer Part Number: ADM488
• Description: Full-Duplex/ Low Power/ Slew Rate Limited/ EIA RS-485 Transceivers
• Manufacturer: Analog Devices

ADM488/ADM489
The ADM488/ADM489 comfortably meets Classification 1 at
the most stringent (Level 3) requirement. In fact, field strengths
up to 30 V/m showed no performance degradation and error-
free data transmission continued even during irradiation.
EMI EMISSIONS
The ADM488/ADM489 contains internal slew rate limiting in
order to minimize the level of electromagnetic interference
generated. Figure 22 shows an FFT plot when transmitting a
150 kHz data stream.
Figure 22. Driver Output Waveform and FFT Plot Trans-
mitting @ 150 kHz
As may be seen, the slew limiting attenuates the high frequency
components. EMI is therefore reduced, as are reflections due to
improperly terminated cables.
EN55022, CISPR22 defines the permitted limits of radiated
and conducted interference from Information Technology
Equipment (ITE).
The objective is to control the level of emissions, both con-
ducted and radiated.
For ease of measurement and analysis, conducted emissions are
assumed to predominate below 30 MHz, while radiated emis-
sions predominate above this frequency.
10dB/DIV
Level
V/m
1
2
3
100
0%
90
10
0
Table IV.
Field Strength
1
3
10
500kHz/DIV
5MHz
–10–
CONDUCTED EMISSIONS
This is a measure of noise that is conducted onto the mains
power supply. The noise is measured using a LISN (Linc Im-
pedance Stabilizing Network) and a spectrum analyzer. The test
setup is illustrated in Figure 23. The spectrum analyzer is set to
scan the spectrum from 0 MHz to 30 MHz. Figure 24 shows
that the level of conducted emissions from the ADM488/
ADM489 are well below the allowable limits.
Figure 23. Conducted Emissions Test Setup
Figure 24. Conducted Emissions
80
70
60
50
40
30
20
10
0
DUT
0.3
LOG FREQUENCY (0.15–30) – MHz
0.6 1
SPECTRUM
ANALYZER
LISN
3
6
10
PSU
30
LIMIT
REV. 0