Other Parts Discussed in Thread: LM3409HV, LM3409
I make my own board of led driver wtih LM3409HV, is very similar to the circuit in AN-1953 LM3409HV Evaluation Board, but different layout.
When set PWM duty cycle lower 95%, the Board generate noisy ringing. I record it and do pectrum analysis to get the follow image:
input PWM frequency is 2KHz。
Then I try to find where is the noise from. I isolate all Capacitor/Inductor/PMOS by wiring these devices to board with thin wire, and use my headphone microphone to record sound of device one by one and findout that noise is generated mainly by LM3409, which supprise me. All I found on web say Capacitor or Inductor generate noise. I'm stuck..
What changes do I need to eliminate the noise?
INPUT voltage: 52
INPUT PWM: 2KHz