LM5117 Switching Noise

insu moon

Prodigy 90 points

Other Parts Discussed in Thread: LM5117

Hello.

I have a design to take 53 volts in, and regulate it to 12.3V/7A.

My issue is with my switching noise. When I increase load then the noise increase as well.

And about 4.5A load LM5117 is turned off. I think it's because of switching noise.

Below picture is a SW pin signal and It has switching spike, ringing signal and some skip switching.

Below picture is a voltage output (12.3V) and I can see switching noise.

And I attached a schematic.

Can anyone help to solve this issue?

Thanks and regards,

Insu

5165.Schematic.pdf

over 9 years ago

0 Garrett Roecker over 9 years ago

TI__Mastermind 21720 points

Hi Insu,

Please post the pictures as they didn't get uploaded last time.

-Garrett

0 insu moon over 9 years ago in reply to Garrett Roecker

Prodigy 90 points

Hi Garrett,

Thanks for your support and I attached two pictures.

Regards,

Insu

0 Garrett Roecker over 9 years ago in reply to insu moon

TI__Mastermind 21720 points

Insu,

Please look at the RAMP signal and make sure there is no noise.

I also notice that the VCC rail is tied to VOUT, which is 12.3V. This is going to drive the MOSFETs on faster thus causing more noise on the switch node. Try using the internal VCC regulator and see if there is any improvement. If you still want to use VOUT as the VCC rail then you can add a small gate resistor on the high side MOSFET gate to slow the MOSFET's turn on.

There may also be noise inducted by the PCB layout. Make sure that standard layout rules were followed.

Thanks,

Garrett

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LM5117 Switching Noise