ISO7741-Q1: solution for improving EMI

Jay wang

Intellectual 2041 points

Part Number: ISO7741-Q1
Other Parts Discussed in Thread: ISO7741, ISOW7741

hi expert

i saw this link Fundamentals of EMI Requirements for an Isolated DC/DC Converter (ti.com). in this note, it show two solution to improve EMI: one is to add "Interlayer Stitching Capacitance"; the other is to "stitch capacitors between inner layers".

BUT, it is NOT for ISO- digital device.

so my question is whether these solutions of improving EMI also are suitable for ISO7741. do we have any APP note or related resource? thanks

4 months ago

0 Aaditya Vittal 4 months ago

TI__Expert 8585 points

Hello,

Thank you for your question.

Please allow us to review the information and get back to you on Monday next week.

Regards,
Aaditya Vittal

0 Jay wang 4 months ago in reply to Aaditya Vittal

TI__Intellectual 2041 points

hi Aaditya

ok.

adding a further question: if need to add "Interlayer Stitching Capacitance", what value of "Interlayer Stitching Capacitance" is recommended?

thanks

0 Aaditya Vittal 4 months ago in reply to Jay wang

TI__Expert 8585 points

Hi Jay,

Thank you for your patience.

It looks like you mean ISOW7741 device. If so, yes stitching capacitor can be used to improve the EMI performance. For more information regarding stitching capacitor, please check Low-Emission Designs With ISOW7841 Integrated Signal and Power Isolator (Rev. C) (ti.com)

Regards,
Aaditya Vittal

0 Jay wang 4 months ago in reply to Aaditya Vittal

TI__Intellectual 2041 points

hi Aaditya

i don't mean ISOW7741. customer use ISO-digital IC(ISO774x).

stitching capacitor solution of Low-Emission Designs With ISOW7841 Integrated Signal and Power Isolator (Rev. C) (ti.com) and Fundamentals of EMI Requirements for an Isolated DC/DC Converter (ti.com) is not special for ISO-digital IC.

So my question is whether stitching capacitor solution also can be used for ISO-digital IC

0 Aaditya Vittal 4 months ago in reply to Jay wang

TI__Expert 8585 points

Hi Jay,

Thank you for your clarification.

Yes, Generally speaking, the stitching capacitor helps improve EMC issues for TI digital isolators, such as the IUSO774x, in order to help with EMC challenges, but it is not required for the operation of the device.

One thing to note is that the stitching capacitor significantly decreases the isolation rating for the overall system/solution.

Regards,
Aaditya Vittal

0 Aaditya Vittal 4 months ago in reply to Aaditya Vittal

TI__Expert 8585 points

Hi Jay,

If possible, please provide us with a brief description of the EMI issue you have faced with the ISO7741 device.

Regards,
Aaditya Vittal

0 Jay wang 4 months ago in reply to Aaditya Vittal

TI__Intellectual 2041 points

hi Aaditya

currently, customer just start to do layout using ISO774x. SO they want to know whether they can use "stitching capacitor" solution to prevent potential EMI issue IN ADVANCE.

0 Clemens Ladisch 4 months ago in reply to Jay wang

Guru 269830 points

The integrated DC/DC converter of ISOW devices generates much more noise (because of the higher power levels).

Plain signal isolators do not have this problem, and usually do not need a capacitor between the grounds. The most important mechanisms to prevent potential EMI issues are decoupling capacitors, and proper termination of the signal lines (if they carry high-speed signals).

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ISO7741-Q1: solution for improving EMI