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PCB grounding

Hi to all,

I am designing a PCB with a digital circuit based on a STM32F103 MCU with USB,LAN and RS232 ports. The power comes from an external wall type

12V/2.5A switching type regulator. There are 3 grounds in my PCB : a digital ground (GND), a connector frame ground (FGND) which is connected to GND through a 3.9nF/1KV capacitor and the input ground (the common which comes from the external power supply) which is connected to GND through a differential line filter.

The pcb according to local regulations has to be enclosed into a metal box and has to be compatible with all CE regulations accordind EMI and ESDs.

In your opinion where the metal frame should be connected ? to GND, to connector frame ground or at the common power supply ground ?

Thanks in advance,

Angelo

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Reply to
abrous
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Your "local regulations" should specify this. Tests can be done to make sure that you got it right.

Most of the time the metal box is connected to frame ground. It makes sense to have the device's "frame" connected there.

Most of the time the USB host will have frame ground shorted to digital ground. That introduces additional problems.

Have fun, RK

RK

Reply to
d_s_klein

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