I designed an USB powered system and I am facing off with several problems caused by USB noise.
On my system a digital part (MCU) and an analog section (DAC and analog circuits) are placed. I separated using filters GND and AGND plane, VCC and AVCC signals but these tricks are not enough to filter noise problem.
The principal noise sources are two and the analog section shows the biggest problem:
1) Noise caused by the USB communication: this is the lower
2) Noise caused by the USB power supply: this is host dependent and the worst case is using my system plug in a notebook pc during battery charging phase (i.e. with the battery charger plugged in 220V)
For the first noise I can place a commone mode filter or EMI filter on the D+ and D- signals.
For the power supply noise I tried to filter the 5Vdc but I am not able to reach good results, furthermore the 5Vdc could not be charged using high value of capacitance.
I am thinking to generate a 5Vdc using a buck-boost converter and then filter this new supply, what do you think about the ADP2503 DC/DC converter?
Other solution and suggest are appreciated,