LM5116: Switching frequency changes under different loads

Kar Tsang

Part Number: LM5116

Hi,

I have an LM5116 with the switching frequency set to 260KHz. 48V input and 12V output. Under 2A load, I can see that the switching frequency varies between 260Khz, 130KHz and 86.6KHz which is half and one third of the set switching frequency. Under higher loads, I can see that the switching frequency is mostly 260KHz. Is this expected behavior or is there a problem with my compensation network/ramp?

Thanks

over 5 years ago

0 Frank De Stasi over 5 years ago

TI__Guru 73225 points

I do not think that the frequency should change that much.

First, check your component design with the calculator found on the product folder for this device.

Second, make sure that your PCB layout conforms closely to the example provided in the data sheet and/or to the EVM layout.

If you need more help, you will need to send us your schematic and PCB layout, along with your input, output and load values.

0 Frank De Stasi over 5 years ago in reply to Frank De Stasi

TI__Guru 73225 points

Hello

I will close this post due to inactivity.

Thanks

0 Kar Tsang over 5 years ago in reply to Frank De Stasi

Prodigy 30 points

Hi, just a quick update, the problem was due to the ramp capacitor. The affects of this capacitor being the incorrect value are documented in the data sheet and it causes sub-harmonic oscillations which is what I am seeing.

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LM5116: Switching frequency changes under different loads