LM5168: Issue with LM5168 Regulator Output

Hi,

This could be due to possible due to miscalculation of ripple. I am unable to read the schematic component values. Can you share the PDF file?. Also recommend you to share the Switch waveform and the output voltage.

Thanks,

Nitya

Hello,

Sorry, the file is not very readable. You will find the file in pdf.
CSU_BMU-Alimentation EMU-BMU.pdf

I'll give you the output voltage, and the voltage on the SW pin.

The input voltage is as follows, a fixed voltage of 60V

Thank you very much

Hi Clement,

The ripple calculation components are not accurate. The Ra(R227) = ~30kohms for proper ripple generation. Recommend you to change the R227 value and test the behavior of the device. 

Attaching the excel tool for reference. 

/cfs-file/__key/communityserver-discussions-components-files/196/LM5169_5F00_calc_5F00_revD_5F00_18Sbattery.xlsm

Thanks,

Nitya

Hello,

The issue is not coming from resistor R227. We have indeed replaced this resistor, but the output voltage still has the same shape. Additionally, by increasing the resistance, we reduce the ripple. Here are the output voltages we obtained and the signals on the SW pin.

However, we removed the diode, and we are now getting a clean 3.3V on the non-isolated side. Here are the output signals we observed and the signals on the SW pin.


We are really stuck and cannot figure out where the problem is. We don’t know how to achieve the correct isolated 3.3V.

Thanks
Clément

Hello,

We have identified the cause of our problem: it was due to pins 3 and 4 of the transformer being reversed. However, we are now facing a new issue. On both the isolated and non-isolated sides of the regulator, the output voltages are extremely noisy.

3.3V non-isolated

3.3V isolated


Pin SW


What can we do to improve these output voltages? We have changed the Ra resistor to adjust the ripple, but the noise persists. Is there any way to fix this issue? Is this level of noise normal?

Thank you.