Comments on ESD USB Shield Connection & Filtering
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ESD USB Shield Connection & Filtering
I have a handheld ARM Cortex M based device, which has a USB input port.
The product is battery powered and there is no metal chassis.
We are going through CE testing, and are having ESD issues at 4kV contact to the USB shield with reproducibility under IEC 61000-4-2.
On the data lines of the USB port, we have TVS diodes that are working and shunt the ESD to PCB GND plane and the Cortex can keep functioning. When we air discharge at 8kV to the USB port, that TVS diode is working and the unit keeps functioning.
However, when we ESD shock the shield of the USB connector 4kV Contact Discharge (as per the standard), we appear to have some kind of ground bounce that can lock-up the unit.
Because the shield is tied to PCB GND and we don't have a metal chassis, what kind of filtering could we to the shield traces to PCB GND on an updated PCB revision which could help?
Would an RC filter (series R, parallel C) on each shield trace work? I'm trying to think of a filter that would dissapte the ESD to some extent before it hits the PCB GND Plane.
The PCB is tightly populated and 6 layers, so there isn't a whole lot of room for like a discrete PCB GND moat.
It's kind of surprising that the TVS diodes dumping ESD into the GND plane don't affect the microcontroller; however, if the shield dumps ESD into the GND plane it has a very strong effect.
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