---
title: "EMC"
url: "https://nearfieldnotes.com/families/emc/"
site: "Near Field Notes"
---

# EMC

Notes for when it fails an emissions scan or an ESD zap.

## Notes

- [USB-C shell](https://nearfieldnotes.com/notes/usb-c-shell/): Should a USB-C shell go straight to ground, or through an RC? Straight, unless an earthed box or cable shield touches it too. An 8 kV zap puts the same 30 A into the board’s ground either way. Through 1 MΩ beside 4.7 nF, the cap is left holding 249 V. Common 0805 caps are rated 50 V.
- [Spread spectrum](https://nearfieldnotes.com/notes/spread-spectrum/): What does spread spectrum do to a buck’s EMI test? Almost nothing at its 400 kHz clock. It takes 10 dB off the 4 MHz reading and 12 dB off 30 MHz.

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Source: https://nearfieldnotes.com/families/emc/