I have a PCB which utilizes a switching reg to charge two large caps to350VDC. Unregulated battery power (6.4V-8.4V) is supplied to this board through a two pin connector. There is also another 4 pin connector through which the board gets a regulated source of power (3.3V) as well as 3 other signals of which one is a charge done signal.
I am having issues with noise on the signal lines when the charge cycle initiates. The noise is at its worst at the beginning of the cycle which seems to indicate it's related to di/dt (current tapers off as caps charge). The noise on the charge done signal occasionally triggers the interrupt prematurely (on another PCB to which the 4 pin connector is attached via 12" 24AWG conductor). Switching frequency is between 100kHz and 300kHz.
The board is 2 layers with the bottom layer serving mostly as a ground plane (a few signals running around). I believe I have a decent layout as far as the high current paths in the switching circuit. Everything is kept as tight as possible (given the large transformer required) and tied with large copper polygons (reducing inductance of traces).
I am revising the board and want to improve the noise situation. First thing I did was I added a RC network to the form a low pass filter right at the 4 pin connector. I suppose I could also use a LC combination. Is there a reason to choose one over the other? Second, and I am not sure this is actually beneficial, I made an L shaped slot to route the high currents in the ground plane back to the 2 pin connector. The thought was to keep those currents out from underneath the signals going back in the 4 pin connector.
Here is a rough image of the PCB layoutI've marked up the signals in RED and the high current paths in YELLOW.
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