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LM5175: LM5175RHF ground noise issue

Berlin Stas
Prodigy 170 points
Part Number: LM5175

B050 _ 11.12V_PS.pdfHi,

Attached schematics buck-boost converter used to convert input voltage 6-24V to output 12V, 3 amp. This power supply serviced for CPU module with miniPCI added card. And now I faced problem that one type of PCIe added card is doesn't work. After careful investigation I understood that switching noise of the PS affect to PCIe functionality. My question is what is the way to reduce this switching noise of the PS

Thank you

Berlin Stanislav

  • 0
    TI__Guru* 78370 points
    Hi Berlin,

    Thank you for reaching out. Do you know whether the problem is caused by the noise at the input port or the output port of the this buck-boost stage?

    Seen from your schematic, you don't have a gate resistor, which may cause high dv/dt and di/dt during switching, inducing some switching ringing, and the ringing is a source of switching noises. Beside, you do not use much input capacitors. Can you add more input capacitors (also add a couple of 0.1uF and 0.01uF to bypass high frequency noises) and see if this helps?


    Thanks,
    Youhao Xi, Applications Engineering
  • 0 in reply to Youhao Xi
    Prodigy 170 points

    Hi,

    What is functionality of the slope pin? How it affect on chip functionality?

    Thank you

    Stas

  • 0 in reply to Berlin Stas
    TI__Guru* 78370 points
    Hi Berlin,

    It generate a slope signal that is used for slope compensation to achieve stability. The LM5175 is a current mode controlled circuit, it requires slope compensation.

    Thanks,
    Youhao