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LM5030: Voltage spikes

Bart
Expert 6470 points
Part Number: LM5030


Team,

We are using LM5030 and have some issues with spikes on CS (R123) resistor.

Those spikes are 2V and CS pin is activated at every period and is triggering overcurrent protection of IC so the output is “choked”.

Below you can see captured waveform of PCB:

Waveform

Component

Ch2

R123

Ch3

Drain of Q2B

Ch4

Drain of Q2A

Those spikes are made by switching of Q2B (schematic attached here: push_pull_converter.pdf).

Outputs are loaded with:

Output

Load

+DC_HS

31.4R

-DC_HS

11R

+DC_LS

31.4R

-DC_LS

11R

 

The maximum VDS of FETs is 100V (http://www.vishay.com/docs/75213/sqjb70ep.pdf)

The VIN is 30V.

  •  Do you have any advice to help us with this problem?
  • 0
    TI__Genius 13660 points

    Hi Bart, an expert will get back to you soon.——Teng

  • 0
    TI__Genius 9790 points

    Hi, Bart

    From your waveform, the voltage waveform of R123 is quite normal. Could you check the waveform on CS pin as along as voltage waveform of R123?

    LM5030 has over current protection on CS pin, if CS exceeds 0.5V, the outputs will go into cycle-by-cycle current limit. If CS exceeds 0.625V, the outputs will be disabled and a soft start commenced. 

    The calculated switching frequency is 290kHz, but the RC filter on CS pin is R122=1K and C152=1nF, the corner frequency is 159kHz, which is not reasonable. The corner frequency of RC filter should be higher than switching frequency. So C152 is recommended to use 100pF.

    Regards,

    Yunsheng