SI8220 SILABS [Silicon Laboratories], SI8220 Datasheet - Page 18

• Manufacturer Part Number: SI8220
• Description: 0.5 AND 2.5 AMP ISODRIVERS WITH OPTO INPUT (2.5, 3.75, AND 5.0 KVRMS)
• Manufacturer: SILABS [Silicon Laboratories]

Si8220/21
6.6. RF Radiated Emissions
The Si822x family uses an RF carrier frequency of approximately 700 MHz. This results in a small amount of
radiated emissions at this frequency and its harmonics. The radiation is not from the IC chip but, rather, is due to a
small amount of RF energy driving the isolated ground planes, which can act as a dipole antenna.
The unshielded Si822x evaluation board passes FCC Class B (Part 15) requirements. Table 12 shows measured
emissions compared to FCC requirements. Note that the data reflects worst-case conditions where all inputs are
tied to logic 1 and the RF transmitters are fully active.
Radiated emissions can be reduced if the circuit board is enclosed in a shielded enclosure or if the PCB is a less
efficient antenna.
6.7. RF, Magnetic, and Common Mode Transient Immunity
The Si8220/21 families have very high common mode transient immunity while transmitting data. This is typically
measured by applying a square pulse with very fast rise/fall times between the isolated grounds. Measurements
show no failures at 30 kV/µs (minimum). During a high surge event, the output may glitch low for up to 20–30 ns,
but the output corrects immediately after the surge event.
The Si8220/21 families pass the industrial requirements of CISPR24 for RF immunity of 10 V/m using an
unshielded evaluation board. As shown in Figure 16, the isolated ground planes form a parasitic dipole antenna.
The PCB should be laid-out to not act as an efficient antenna for the RF frequency of interest. RF susceptibility is
also significantly reduced when the end system is housed in a metal enclosure, or otherwise shielded.
The Si8220/21 digital isolator can be used in close proximity to large motors and various other magnetic-field
producing equipment. In theory, data transmission errors can occur if the magnetic field is too large and the field is
too close to the isolator. However, in actual use, the Si8220/21 devices provide extremely high immunity to external
magnetic fields and have been independently evaluated to withstand magnetic fields of at least 1000 A/m
according to the IEC 61000-4-8 and IEC 61000-4-9 specifications.
18
Frequency (MHz)
1424
2136
2848
4272
4984
5696
712
Measured (dBµV/m)
Table 12. Radiated Emissions (Preliminary)
29
39
42
43
44
44
44
Figure 16. Dipole Antenna
GND1
Rev. 0.22
Antenna
Dipole
Isolator
FCC Spec (dBµV/m)
37
54
54
54
54
54
54
GND2
Compared to Spec (dB)
–15
–12
–11
–10
–10
–10
–8