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LM5175: Output noise

PYTsai
Genius 11495 points
Part Number: LM5175

Hi,

We are using LM5175 and see noise at the output, may i get your suggestion how to adjust my schematics to improve. The symptom and my schematics attached as below. 

 

1. Waveform 1: Vin = 6.6V, 3.62A.  Yellow – DC12V;  Blue – VBAT_FILT_SW;  Pink – SW1; Green – SW2

2. Waveform 2 :  Vin = 17.2V / 1.26A;  Yellow – DC12V; Blue – VBAT_FILT_SW; Pink – SW1 ; Green – SW2

3. Waveform3: Vin = 13.5V / 1.61A ;  Yellow – DC12V;  Blue – VBAT_FILT_SW ; Pink – SW1 ; Green – SW2

     

  • 0
    TI__Guru* 78070 points
    Hi PY,

    It seems you enabled the frequency dithering. Is this what you want or you just copied the EVM or datasheet schematic but it is not intended in your design?

    For the switching noise on the output rail, it may not be realistic but induced by improper probing on the PCB. You should use a probe with short ground coil tip rather than the regular long ground lead, to measure the Vout ripples.

    If you still see such noise, you should add some high frequency capacitors like 0.01uF and 0.1uF at the output rail to filter it out.

    Thanks,
    Youhao Xi, Applications Engineering