SI8421 Silicon Laboratories, SI8421 Datasheet - Page 22

• Manufacturer Part Number: SI8421
• Description: (SI8410 - SI8421) SINGLE & DUAL-CHANNEL DIGITAL ISOLATORS
• Manufacturer: Silicon Laboratories

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Si8410/20/21
4.4. RF Immunity and Common Mode Transient Immunity
The Si841x and Si842x 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 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 Si841x and Si842x families pass the industrial requirements of CISPR24 for RF immunity of 3 V/m using an
unshielded evaluation board. As shown in Figure 14, the isolated ground planes form a parasitic dipole antenna,
while Figure 15 shows the RMS common mode voltage versus frequency above which the Si841x 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 15. 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.
22
5
4
3
2
1
0
500
Figure 15. RMS Common Mode Voltage vs. Frequency
GND1
Figure 14. Dipole Antenna
1000
Preliminary Rev. 0.1
Frequency (MHz)
Antenna
Dipole
Isolator
GND2
1500
2000