About LM5117 overcurrent protection --- from a provincial competition question in 2016

2429129589

This is an old question from the 2016 TI Cup Provincial Competition about designing a step-down DC switching power supply using LM5117.

I have been learning related knowledge recently, and there happened to be some solutions to this problem on the Internet, so I downloaded it and took a look.

At present, most of the content has been understood, but there are still some doubts about the over-current protection mentioned in the competition question.

The competition question asked:

In the competition materials I found, the students’ solution at that time was as follows:

But I am curious, based on my understanding of the LM5117 manual, doesn't the 5117 have its own overcurrent protection ?

There are even three modes to choose from:

I would like to ask you to help me analyze whether the method used in the competition material I found is redundant or I have misunderstood the manual of LM5117.

Finally, I have another question. If I want to use LM5117 to achieve adjustable output voltage :

Can I just add potentiometers to FB2 and FB1?

Thank you all for your help.

maychang

"Finally, there is another question. If I want to use LM5117 to achieve adjustable output voltage , can I just add a potentiometer to FB2 and FB1?"

The output voltage is controlled by changing the ratio of FB1 and FB2.

chunyang

Competition is not a practical application, so it is OK to not use the on-chip protection function but to require it to be implemented separately. For actual product applications, it is certainly not unnecessary unless the on-chip circuit cannot meet some special requirements.

2429129589

chunyang posted on 2019-12-18 14:45 The competition is not a practical application. It is of course possible to require additional implementation without the on-chip protection function. Of course, it will not be redundant for the actual application of the product, unless the on-chip...

Then I can just use the overcurrent protection built into the chip, is that right?

topwon

The overcurrent protection provided by 5117 is only used to prevent the output switch peak current from saturating the inductor and to prevent the output from short-circuiting to the ground. The circuit built with the op amp is used to limit the output load current (which has been filtered), and this current limit value can be adjusted as needed.

chunyang

2429129589 Published on 2019-12-19 08:21 Then I can just use the overcurrent protection built into the chip, is that right?

The specific application is of course, and the competition is based on the rules of the competition.