LM5122: Boost Circuit is not working LM5122

Hello BHARGAV ITALIA,

From the schematic, I cannot see a generic failure at the first glance. Could you please add some oscilloscope measurements especially from VIN, VOUT, UVLO and SS at the moment when you turn on your power supply? Please zoom in to anything that is suspicious.

Best regards,
Brigitte

Brigitte,

Thank you for taking time to check on my post. I've attached the measurements of mentioned pins here. Can you please advise if you see something not right?

CH1=SS,CH2=UVLO,CH3=VOUT

CH1=VIN,CH2=SS

Thank you!

Hello BHARGAV ITALIA,,

It seems that something causes softstart to get regularly discharged over and over again. Softstart would normally need to get charged and then stay charged. 

Looks like hiccup mode, please check if R5 is the right value and try to measure the voltage drop on R5. 

Best regards,
Brigitte

Hello BHARGAV ITALIA,,

Please measure the VCC, and the gate signals and keep SS as reference. Please always measure the signals in reference to the GND of the IC.

You could try to increase the UVLO a bit to check if this changes anything.

For your measurements, did you start into load? If yes, which load are you using?

Best regards,
Brigitte

Brigitte,

Hello Bhargav Italia,

Which signals are on this scope plot?

Best regards,
Brigitte

It's CH1=SS,CH2=Vcc,CH3=LO,CH4=HO

I apologize, I forgot to mention that.

Hello Bhargav Italia,

SS is connected to a constant current load. I do not understand why this is permanently charged and discharged. Can you keep the measurement signals and zoom in to the first start attempt?

On the other hand, I wonder if anything damaged the IC. Do you possibly a second board that you could check?

Best regards,
Brigitte

I have tried a couple IC's with the same problem. I will try building up a different board and see if I get the same result.

This the first attempt of the SS signal

Hello Bhargav Italia,

Is the signal 2 still VCC? Why is it such low? Please measure always the way that the fill signal can be seen. What is happening when SS suddenly gets pulled up? Is this happening everytime after SS goes slowly high and then suddenly gets pulled very high?

Best regards,
Brigitte

You are correct  I connected ch 2 to UVLO by  accident.

Here is the wave form with Ch1= SS Ch2 =Vcc  Ch3 =LO Ch3=HO

The noise pulse only appears on the first one or two startup attempts

Hi Bhargav,

From SS, it seems the IC is restarting over and over again.

Can you share the steady state waveform? And can you share the layout?

Best Regards,

Feng Ji

I agree it appears to be restarting. What steady state waveforms would you like to see?

here are pictures of the board layout 

Board Layout

Front Copper

Bottom Copper Mirrored

Top Components

Bottom Components Mirrored

Hi Bhargav,

BHARGAV ITALIA said:

Here is the wave form with Ch1= SS Ch2 =Vcc  Ch3 =LO Ch3=HO

The noise pulse only appears on the first one or two startup attempts

 

I want to know what is the reference of HO? HO-SW or HO-AGND?

Please share SS, HO-SW, LO, RES waveforms.

It can be seen from the layout that you are not following Kelvin Connection for CSN and CSP.

Best Regards,

Feng Ji