Dear Support Team,
In the ISO121x datasheet, Table 3 I find CIN specified as 330nF for surge protection of Type 3 input scheme at +/-1kV Line to FGND (see below):
Compared to the 10nF specified for a Type 1 input, I wonder, why the value for Type 3 is 33 x higher? (Or is this simply a typo as I suspect?)
Best Regards
Simon
Hi Simon,
Sorry for the delay in getting you an answer. Thank you for your patience.
ISO1212 can handle about 0.5A of peak surge current between line and FGND. This corresponds to 500V surge voltage with a 1kOhm series resistor (type 3). To achieve >500V surge performance with 1k series resistor, we need to filter out the surge voltage/current – hence the CIN value needed becomes very high.
At the same time, if the surge test is performed between line and PE (not input and FGND), the surge current is attenuated by the barrier capacitance, so a high CIN is not needed.
If line to FGND surge tolerance of >500V is needed while designing for Type 3, TVS diodes may be used per Fig 24 of the datasheet.
For type 1, with a 2.5k series resistor, the current for 1kV surge is about 250mA, which ISO121x can handle without high CIN filtering.
Please let me know if this answers your question.
Have a great weekend!
Dan
