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ISO7842: About layout Example schematic

Part Number: ISO7842

Hello,

There is a schematic example in Figure 21. There is numbers 10 mils, 40 mils and 10 mils in vertical direction.

The numbers are for maintaining the impedance for high speed data, not for isolation barrier. The distance can be changed if we can control the impedance. Is my understanding correct?

There is a slit under IC in figure 21. Is this slit needed? If yes, is it for maintain the creepage distance?

Best regards,

Toshihiro Watanabe

  • Hi Toshihiro-san,

    The spacing values between PCB layers given in Figure 21 of ISO7842 datasheet are only example values and are not calculated numbers. Like you have mentioned, these numbers are not related to isolation barrier and customers can choose the spacing between PCB layers to best suit their requirement.

    You are right, the slit is to increase creepage of the PCB. Most TI isolators are of Material Group I type hence support very high isolation specs for a given creepage distance. While the PCB material is generally lower in Material Group hence customer may need higher creepage on PCB than on ISO7842 to support full isolation specs of ISO7842. If customer application isolation requirement doesn't require a slit, then there is no need to create a slit. Thanks.


    Regards,
    Koteshwar Rao