ElectroStatic Discharge — the spark when you touch a doorknob. Can fry exposed chip pins.
How it looks
Real image: CORE3588, rendered by KiCad from our board file
ESD protection on CORE3588, top side, 11 x 7.6 mm. Every connector a person can touch has one: D5 here, D3 for the SD card, D9 and D10 on the debug header, D8 on the button.
1D5: a tiny ESD protection chip, placed right next to the USB-C socket so a spark from the cable meets it first.
2The USB-C socket: the place a charged hand or cable touches.
Real image: the CORE3588 schematic, exported by KiCad (shown in greys)
The debug header's two protection diodes (D9, D10) in the real schematic.
1D9: from the debug TX wire to ground.
2D10: from the debug RX wire to ground.
How it works
Where it fits
ESD parts are a kind of TVS diode. Radiated noise is EMI; the product tests are FCC / CE.