LM25118: Loading of LM25118

lee peng kiat

Intellectual 450 points

Part Number: LM25118

Hi,

Input voltage to LM25118 is around 12V, then the output voltage is 12V.

When the output loaded to about 1.1A, the high side & low side gate driver keep on adjusting duty cycle non stop.

Then it cause the output to generate 1V ripple (15KHz sinewave noise).

This chip suppose can be load with 3A, therefore I don't think it cause by max current rating.

May I know what is reason behind to cause this problem ?

Thanks

over 6 years ago

0 Garrett Roecker over 6 years ago

TI__Mastermind 21720 points

Hi Lee,

It sounds like it might be related to the compensation of the control loop. Please use the LM25118 quick-start calculator to double check the loop compensation values.
www.ti.com/.../lm5118quick-calc

Thanks,

Garrett

0 lee peng kiat over 6 years ago in reply to Garrett Roecker

Intellectual 450 points

Hi Garrett,

Thanks for your reply.

The surrounding circuit and all the components value in my design are same to LM25118 Evaluation board,

except for the MOSFETs & Schottky Diodes which are difference but their spec are about the same to parts used in EVK board.

The values for the compensation circuit should be optimum in EVK board ?

I don't have the evaluation board to test for it.

Thanks

0 Garrett Roecker over 6 years ago in reply to lee peng kiat

TI__Mastermind 21720 points

Lee,

At full load are you seeing the duty cycle change? Also please post a screen capture of the changing duty cycle. You might just be right around the transition region between CCM and DCM. This could make the it look like the duty cycle is changing continuously.

-Garrett

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LM25118: Loading of LM25118