Or-ing Power EMI

[antercreeper]

I am designing a FPGA board and suffer from EMI issue. While plugging in second USB (as slave, the first acted as power source), buttons will be false triggered(some spikes injected), as the power source 1 and power source 2 comes from different adapter(2 pin without ground) and have about 60 volts between them.
What do i need to add? I have seen some solutions, for example tvs, ferrite bead(some in vbus, others in gnd), common chokes on power lines...

[selcuk]

Is the 5V ground potential difference 60V, or protective earth ground? Apart from that you may connect ground and shield of the USB connectors together and to the board ground. Remove C30 an L9 and make a short and low inductance ground connection. So that you will have a single ground net on the board.

[antercreeper]

thanks for replying. sorry for my bad english.
what my questions is... two dc inputs have two grounds(of course soon generate a loop from Y cap of one adapter(virtual earth) to the other adapter's really 0 volts earth ground)......
so When hot plug, a surge confused my chip......
maybe a common choke is ok?

[antercreeper]

For my design(no enclosure, so no earth ground)(haven't been tested yet.)
The first DC input:

the VINADA is to DC-DC buck regulator(1*22uF SP-CAP, 2*33uF aluminum, 1*1uF ceramic, all 25 volts max, act as regulator's input caps, maybe can handle surge from inductor?) and convert 19V to 5V, and then two PMOS gates.

The second DC input from USB:

 

[selcuk]

I agree. A surge current which equalizes the ground voltages may cause a voltage difference on your circuit ground. So I can suggest to decrease the ground inductance to lower that ground shift voltage. You may try shorting the ferrites separating the grounds, with 0 ohm resistors. Common mode chokes may block this current if it is not differential but I'm not sure.

[antercreeper]

Thanks.