I have many IR leds to drive, with MOSFETs and a single constant 60 mA low side current regulator. The leds are PWM at 1 MHz (50% duty cycle), and the farthest leds are 60 cm away from the regulator.
I am not very experienced with EMI, but from what I read:
- I need to "round" the PWM signal to avoid high resonant frequencies
- I need to keep the loop area as small as possible
- I need to keep the return traces to ground as small as possible
It is not a problem to route the return trace of each led just beneath the power traces on the adjacent PCB layer.
My main concern is about the very long return traces (60cm) which are required to reach the low-side current regulator.
At 1 MHz / 60 mA, do you think it would cause EMI issues, should I use multiple current regulators at regular intervals ? Would you have any suggestion to reduce EMI (besides lowering the frequency)
Generally speeking, provided that the topology/layout allows it, what are the benefits of a ground plane for handling return path, over dedicated return traces (in terms of EMI) ?