SI8440 SILABS [Silicon Laboratories], SI8440 Datasheet - Page 17

• Manufacturer Part Number: SI8440
• Description: QUAD-CHANNEL DIGITAL ISOLATOR
• Manufacturer: SILABS [Silicon Laboratories]

4.4. RF Immunity and Common Mode Transient Immunity
The Si8440 family has 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 up to 30 kV/µs. 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 Si844x family passes the industrial requirements of CISPR24 for RF immunity of 3 V/m using an unshielded
evaluation board. As shown in Figure 15, the isolated ground planes form a parasitic dipole antenna, while
Figure 16 shows the RMS common mode voltage versus frequency above which the Si844x becomes susceptible
to data corruption. To avoid compromising data, care must be taken to keep RF common-mode voltage below the
envelope specified in Figure 16. 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.
5
4
3
2
1
0
500
Figure 16. RMS Common Mode Voltage vs. Frequency
GND1
Figure 15. Dipole Antenna
1000
Frequency (MHz)
Antenna
Rev. 0.3
Dipole
Isolator
GND2
1500
Si8440/1/2
2000
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