LM5036: The power-off timing issue of the auxiliary power supply of the IC

peng cheng

Part Number: LM5036

Tool/software:

A 200W power supply was designed using LM5036. During the process of cutting off the input voltage,

it was found that the auxiliary power supply did not decrease along with the drop of the input voltage, but instead showed a repeated oscillation process.

Is this a normal phenomenon?

The phenomenon that the waveforms of ten circuit boards were all accessories was tested

4 months ago

0 peng cheng 4 months ago

Prodigy 60 points

This is schematic

0 Hong Huang 4 months ago in reply to peng cheng

TI__Guru 74095 points

Hi,

LM5036 relies on the excel design sheet quite heavily. Please provide your LM5036 excel design sheet to review as we need to understand if your design is following the excel sheet first.

0 peng cheng 4 months ago in reply to Hong Huang

Prodigy 60 points

This circuit works normally when the input voltage drops from 60V to 24V and the output voltage is 24V.

When conducting a power-off test with an input of 60V, the 24V main power supply was light load(<2w).

.I would like to understand whether the test waveform of the above-mentioned auxiliary power supply being powered off is normal.

Isluc654a.xlsxs this in line with the control logic of LM5036?

0 Hong Huang 4 months ago in reply to peng cheng

TI__Guru 74095 points

Hi,

Yes, that excel sheet should be used for the design but need to fill in your design related numbers.

When power off, the AUX oscillation seems your design triggering AUX on/off repeatedly - as this is during power off, if ok to tolerate, it is up to you and applications. I need you to provide your full schematics and filled in excel sheet to review to see if able to minimize or eliminate the oscillation.

0 peng cheng 4 months ago in reply to Hong Huang

Prodigy 60 points

The attached file contains relevant figures that have been modified according to my actual schematic diagram. The schematic diagram is the picture attached above.

0 peng cheng 4 months ago in reply to peng cheng

Prodigy 60 points

Can you judge from your historical experience what the normal power-off sequence of this auxiliary power supply is like?I want to know what the normal standard waveform is like?

It's not necessary to solve this problem immediately. Is it possible that the current oscillation is a normal waveform?

0 peng cheng 3 months ago in reply to Hong Huang

Prodigy 60 points

Dear Huang,

Could you please help reply to this question when you are free?

This is very important for our project!

0 Hong Huang 3 months ago in reply to peng cheng

TI__Guru 74095 points

Hi,

Please provide your full schematics about LM5036. I cannot make analysis on partial schematics.

0 peng cheng 3 months ago in reply to Hong Huang

Prodigy 60 points

I tested it with EVM. The power-off process of the auxiliary power supply was also like this waveform.

I need to understand whether this is a normal situation. Have you analyzed this part of the content before?

0 Hong Huang 3 months ago in reply to peng cheng

TI__Guru 74095 points

Hi,

I already replied. It is due to the UVLO back on during the power off. Usually it is not an issue since it is at power off. But if your application cannot tolerate then we need to find a way to resolve.

Basically you need to tune up or add some circuit to make sure UVLO not back on during power off.

So is it ok to tolerate this or your application cannot?