LM5170-Q1: What behavior will LM5170 do after reach OCP?

Hi Ann,

Exactly. Cycle by cycle peak current limit will be triggered.

Best Regards,

Feng JI

Hello Feng,

I means when the cycle by cycle limit is triggered, what behavior we will see on LM5170? I think we will see the output voltage drop down and it will not shutdown since we don't have UVP, right? Thanks!

Best regards,

Ann Lien

Hi Ann,

You are right.

Best Regards,

Feng JI

Hi Feng, 

Based on your comment, so the Ipk of our design = 34K*1.1u/0.04 = 9.35A, which means the current limitation of this part is 9.35A, is that true?

Moreover, based on the following design, except the IPK, is there any other OCP for this block? thank you.

Hi William,

Your calculation is correct.

Please use the LM5170 design calculator. Please note Rramp may also influence the peak current limit. You must follow the calculated Rramp in the design calculator.

There might be other current limit in the schematic

1.U49 and U52 perform a current limit function

2.Max ISETA voltage may also limit the current.

Best Regards,

Feng Ji

Hi Feng, 

Thanks for your reply,

regarding this circuit, actually, we did the power measurement previously,

and the real measurement of the OCP is around 6.08A per channel, but to use your design calculator,

There will always be a gap with the real value, if possible, could you please help us check the ideal limit current,

I also put this circuit for you to reference, thanks for your great effort!

Hello William,

I will delete your schematic since it is external forum. And I will send email for your circuit to Feng. Thanks!

Best regards,

Ann Lien

Hello Feng,

I've already sent to you for customer's circuit and please take it as reference. Thanks!

Best regards,

Ann Lien

Hi Ann,

Let's go on by email.

Best Regards,

Feng Ji

Hi Feng, Ann,

Do you have any further comments for this question?

Hi William,

As requested by Ann, this thread is being supported by email.

Best Regards,

Feng Ji

Hello Feng,

As talked, please reply result on this thread. I only sent those confidential documents to you. Thanks a lot!

Best regards,

Ann Lien

Hi William,

William Wu said:

and the real measurement of the OCP is around 6.08A per channel, but to use your design calculator,

I found from your waveform that 6.08A is the average output current.

The inductor peak current will be higher than 6.08A.

Please also attach your design calculator.

Best Regards,

Feng Ji

Hi Feng, 

Actually, we don't have this kind of design calculator,

this design was provided by Israel TI FAE, and they told us the OCP can be among 12A (6A/ch),

unfortunately, we're unable to contact this FAE again,

and currently, we just want to know how to calculate it to meet our ideal value "12A (6A/ch)",

thank you.

Hi William,

Please fill in LM5170 design calculator.

From the waveform, the OCP is around 13A for two phases. This is quite close to 12A.

What is your question then?

Best Regards,

Feng Ji