SI823X Datasheet, PDF (28/52 Pages) Silicon Laboratories – 0.5 AND 4.0 AMP ISODRIVERS (2.5 AND 5 KVRMS)

Si823x
6. RF Radiated Emissions
The Si823x family uses a 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 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 Si8230 evaluation board passes FCC Class B (Part 15) requirements. Table 11 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.
Table 11. Radiated Emissions
Frequency Measured FCC Spec Compared to
(MHz) (dBµV/m) (dBµV/m) Spec (dB)
712
29
37
–8
1424
39
54
–15
2136
42
54
–12
2848
43
54
–11
4272
44
54
–10
4984
44
54
–10
5696
44
54
–10
6.1. RF, Magnetic, and Common Mode Transient Immunity
The Si823x 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 Si823x families pass the industrial requirements of CISPR24 for RF immunity of 10 V/m using an unshielded
evaluation board. As shown in Figure 20, 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 Si823x 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 Si823x 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.
GND1
Isolator
GND2
Dipole
Antenna
Figure 42. Dipole Antenna
28
Rev. 0.3