Near Field Notes

Families2 notes

EMC

It fails an emissions scan or an ESD zap.

Find your problem

What is the board doing wrong?

  1. aESD zap on a connectorUSB-C shell
  2. bFails conducted EMISpread spectrum

Notes

2 notes
The circuit
Fig. 2The gun: 150 pF at 8 kV, behind 330 ΩStraightGun30 AShell4 tabs1 nH eachThrough an RCGun30 AShell1 MΩ4.7 nFFig. 2The gun: 150 pF at 8 kV, behind 330 ΩStraightGun30 AShell4 tabs1 nH eachThrough an RCGun30 AShell1 MΩ4.7 nFFig. 2The gun: 150 pF at 8 kV, behind 330 ΩStraightGun30 AShell4 tabs1 nH eachThrough an RCGun30 AShell1 MΩ4.7 nF

Note 2USB-C shell

Should a USB-C shell go straight to ground, or through an RC?

249 → 0 Vleft on the shell after an 8 kV zap

USB-C · GCT USB4105 · CM5 IO board

The drop at each harmonic
Fig. 6eDrop, dB5101500.41 MHz10301 dB10 dB12 dBFig. 6eDrop, dB5101500.411030 MHz1 dB10 dB12 dBFig. 6eDrop, dB5101500.411030 MHz1 dB10 dB12 dB
  • TI’s pattern
  • Triangle only

Note 6Spread spectrum

What does spread spectrum do to a buck’s EMI test?

−10 dBat 4 MHz, quasi-peak

LM62460 · MNT Reform