Hi Luke,

You can set constant current by ISNSP and ISNSN.

You may need to change R6 to change the current limit.

Best Regards,

Feng Ji

My parts are arriving today to test this out, however I had 15A load on the Evaluation Module and it was not yet in constant current mode... It has a 4mOhm resistor for R6, so for 50mV, it should limit at 12.5A, correct? Or is there another way to calculate the resistor R6?

Hi Luke,

We will check this and come back to you soon.

Best Regards,

Feng Ji

Okay, great!

I will do these modifications and report back! However, where in the datasheet did you come up with the IMONOUT RC network values?

Does it simply just need to be the 3-5x faster than the compensation network??

Is it okay to use switch number 15, as it enables the current limit as well? I would like to use the hiccup mode and want a slightly higher PSM entry power....

One more thing, I plan to sense the output current using the IMON pin as well, is it possible to read the pin even with the RC network?

Thanks for your help!

Hi Luke,

Yes, the filter is based on the 3-5 times faster than the compensation network. We are just working on an improved method to get to the compensation values for the IMONOUT in current limiter mode but this will take some more time - perhaps 2 weeks.

You can use all settings where the ILimit is enabled - yes, also 15 does work.

With the Limiter enabled you will not see the current as with the monitor - the signal at 

There are some options to get this:

- use the LM51772 - this will provide this via the CDC signals (but the max voltage is lower for that device) - this is in sampling state now

- use the IMON feature and build the current limiter function externally, see: https://www.ti.com/lit/an/snvaa51/snvaa51.pdf

Best regards,

 Stefan

Stefan,

Thank you for your help so far, I have some more questions now...

Do you have an update on the way to calculate the IMONOUT in current limiter mode?

Also I cannot understand why the constant current varies so much...

I set it at 5A with a 10mOhm resistor...

I modified the Evaluation model to the values you gave me... Additionally, after some Webench designs for my application, I changed the inductor to a 10uH, adjusted the output voltage to 18.4V, and adjusted the COMP network.... 

However, before these latest changes and after the latest changes, the constant current varies a lot... At 11V output, the current is more than 12A!! More than double my desired 5A.... At 17V, the current is very nearly 5A....

I am confused why Webench tells me to use a 22nF and 3.32k RC network, and you say to use a 500R and 2.2nF... Is the Webench designer incorrect?

I discovered that the Webench Design wanted a 3mOhm resistor on the input current sense, so I removed one of the 4mOhm to make it 2 in parallel for 2mOhms... And now if I take the CV under 15V, the board starts audibly squealing and the output current drops to 0.2A... So the constant current is not working at all for some reason...

Hi Luke,

Thanks for reaching out. It would be great if you could fill out the Quickstart Calculator for the LM5177.
Stefan will then continue to support you based on your feedback.

Thank you and best regards,
Bryan

Thank you for the calculator reference, as it makes a complete different circuit than Webench for some reason....

However, my circuit is now built exactly as the calculator suggests, and the buck mode works perfectly....

20.5V 5.5A CC CV output when the input is above 25V... As soon as the input drops below 25V, the inductor makes very audible squeals and the output voltage and current jump around uncontrollably....

I'm assuming COMP and SLOPE need to be adjusted, but I don't know where to start....

Hi Luke,

Please check that the loop compensation is stable in the whole operation range (Vin,min to Vin,max)

It would be good if you can share the calculator with your settings.

Best regards,

 Stefan

https://www.dropbox.com/scl/fi/q8ehleknp78i7hw5pf3p7/LM5177-Buck-Boost-Testing.xlsx?rlkey=coz4jaivlp0kfdrda54pewxb7&dl=0

https://www.dropbox.com/scl/fi/8rz7qbnpyipad03cc1jlz/LM5177-Buck-Boost-Quickstart-Tool-V1_0_9.xlsm?rlkey=duh9j60ryh8ho3q2vrncugix7&dl=0 

Here is the calculator and my testing results, the yellow means an audible noise....

I'm not sure how to check the loop compensation across the range of Vin...?

LM5177 Buck-Boost Quickstart Tool V1_0_9.pdf

LM5177 Buck Boost Testing.pdf

Hello Luke,
As you already have a filled-in version of the Quick Start Calculator, can you please use the Insert - Inage/Video/File function and attach the Excel sheet.
We have limited resources, and this would save all the time to copy the numbers from the pdf.

Thanks and regards,
Harry

LM5177 Buck-Boost Quickstart Tool V1_0_9.xlsm

Can you open this file?

Is there a better recommendation part for my application or why will it not work?

Since Stefan resolved the CC issue in buck mode by sharing the ideal RC filter for the IMONOUT pin, I am marking this solved and have opened another thread for my COMP and slope issues with the same circuit, see 

LM5177: Unstable CC CV Mode Compensation and Slope Settings