LM5118-Q1: Boost problem

Geraldo Gomes

Intellectual 365 points

Part Number: LM5118-Q1

Dear all,

I have a LM5118-Q1 buck boost SMPS with the following basic specifications of project:

Vin: 10V - 30V

Vout: 12V

Iout: 1A

When I insert power with the SMPS loaded with 22R the circuit starts to buzz and the

output become unregulated like the image bellow:

If I do the opposite, that is, I connect the load after the power input is established the problem doesn't appear.

What it can be?

Thanks in advance.

Geraldo Gomes.

over 7 years ago

0 Geraldo Gomes over 7 years ago

Intellectual 365 points

Here is the image

0 Garrett Roecker over 7 years ago in reply to Geraldo Gomes

TI__Mastermind 21720 points

Hi Geraldo,

If possible please post the schematic.

What is the input voltage that you are trying to start up at? Does this happen at every input voltage.

Since it starts up unloaded but not loaded the device might be running into current limit hiccup mode. Try increasing the soft-start capacitor to ease the initial in-rush current.

Thanks,

Garrett

0 Geraldo Gomes over 7 years ago in reply to Garrett Roecker

Intellectual 365 points

Hi Garret,

Thanks a lot for your help!
Really, the device was in hiccup mode, I increased the ss capacitor and the problem was solved.

Beste regards,

Geraldo Gomes.

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LM5118-Q1: Boost problem