LM5143-Q1: Buck Controller Output issue.

Hello Tejendra

Please check SS, COMP at first. If both signals up, then please check if any signals at the HO or the LO pins. 

Your schematic looks fine. 

-EL

Hi EricLee,

I have checked the pins SS, COMP. The voltage at SS pins is 4.96Vdc and Voltage at COMP Pin is 3.296 Vdc. Is there any thing other to check??

Regards.

Hi EricLee,

I have attached the HO1 and LO1 Signals we measured in the Oscilloscope, please refer to them and share your comments on this.

Regards.

https://workdrive.zohoexternal.com/external/10ab13450d9b1ae43ee6b90b6953030d625253ce5a2bf45dff04cf58414cce8b

Hello Tejendra,

Please can you post a clearer picture of your schematic and the BOM also please can you fill out the calculator spreadsheet of the specification your power converter is designed to, will help us narrow down potential cause.

Thanks.

LM5143DESIGN-CALC Calculation tool | TI.com

David.

Hello Tejendra

Also, Please let us know the Y-axis scale of each waveforms, and let us know why HO signal goes down below the ground level. 

-EL

Hi EricLee,

We found the Issue and the Controller is working and the issue is with Dboot and FB1.
but there is an issue like the output is varying with different loads. Can you tell why it's happening? I have attached the schematic and test results. The Variation is about 700mV.
We need to work with it for 10 Amps.

https://workdrive.zohoexternal.com/external/1c40b44ed67f95ff608473712ea023a2298639a4a5393527a3a73227840ebf1b

Hello Tejeda

Looks like there is a component whose value changes over temperature, or your system is unstable and output voltage ripple is too much.  Please measure inductor current and confirm the switching is stable before measuring the output voltage.

-EL 

Hello Ericlee,
We are looking into it.
And I would like to know the usage of 2nd channel when we use interleaved single output. What exactly does the 2nd channel do in this mode? Does the 2nd channel fulfill the current requirement if the 1st channel fails to generate the required current ??

My Requirement is 10 Amps so If I limit the Current output of channel 1 to 2 Amps, does the remaining current requirement is fulfilled by channel 2 ??
or the 2nd channel is only used to reduce the temperature. Kindly let me know this.

Hello Tejeda

Ideally, CH1 supplies 5A and the CH2 supplies 5A when the load current is 10A. The LM5143 device tries to equally share the load current between two channels. 

If CH1 is current limited at 2A, both CH1 and CH2 will enter the hiccup mode protection.

-EL

I am closing this thread since I have not heard from you for sometime.
If you are still trying to resolve the issue, please feel free to open a new thread. Thanks
- EL

Hi Eric Lee,
We are getting the output bust the Buck is getting shut down suddenly after some time. I have taken the temperatures of IC and Mosfets they are at a range of 55 degC. I have attached a result table. S.No 1 shows the working state but it will shut down after some time. What may be the reason please suggest a solution for this.
Regards

Hello Tejendra,

If you are saying that the output of the buck is shutting down as you increase output current, I think you are hitting current limit, can you slightly lower your current sense resistors and retest, I suspect this might solve your problem.  Hope this helps.

David.

Hello David,

We have kept the Current sense resistor value 5mOhms which is 20Amps supported. We required only 10 Amps and now we applied the load of 9 Amps Still we are facing the issue. This is happening when the Buck Board is setup for long hours testing. 1st 30 mins its working fine but later on the voltage is dropping.
Regards

Hello Tenjendra,

I would measure the switch node voltage and ensure the design is still stable.  also check the feedback voltage when output is dropping, Vref will drop if you are hitting current limit.  You will need to check your layout if you design matches with the calculator recommendations.  

Feel free to reopen thread if you are facing issues, please post your schematic along with the calculator spreadsheet filled out to your requirements so we can check you have a robust design.  

Thanks.

David.

Hi David,
I will take a look at the feedback voltage meanwhile Please go through the attached link for the schematic and share your observations.

Regards.
https://workdrive.zohoexternal.com/external/10ab13450d9b1ae43ee6b90b6953030d625253ce5a2bf45dff04cf58414cce8b

Hello Tejendra, the schematic is fuzzy, can you post a higher resolution so I can read.  thank you.

David.

Hi David,
Please go through the Link.for the schematic
https://workdrive.zohoexternal.com/external/fe2f636e965b16df65ca35d9343f9e2d8748d7180bfb1c383c06ce3df8e7ae0f

Thanks Tejendra,

I have noticed you have not filled out the calculator spreadsheet, I request in a previous thread.  it would be very helpful for me if you can kindly fill in your requirements, so I can check your values you have selected.  Also, can you give me the part number of the inductors you are using also?  Here is the link to the calculator spreadsheet.

LM5143DESIGN-CALC Calculation tool | TI.com

Thanks.

David.

Hi David, 

Please go through the link for the calculator spreadsheet.
https://workdrive.zohoexternal.com/external/63ea8b9b87213eb65e20f89e5e766576c69df229b2224992a4188ce193c18a08

Regards

Hello Tejendra,

I checked the spreadsheet; one observation is that you will be operating in frequency fold back mode.  your off time will be 50ns, without taking into consideration of the voltage I*R drops in your power stage.  

I noticed earlier in the thread you had made modifications to the design and you made some improvements; please can you post latest schematic with updated schematic if not done so already, as well as switch node waveforms of your converter before the converter is shutting down.

Thanks.

David.

Hi David,
We tried to keep the Maximum of the components as per the Evaluation board except for the inductor. Before as per the calculations the RT resistor is 54.9KE now it is 10KE as per the eval schematic. 
 
Regards

Hi David, 
I have attached the signals and the link has been provided please check.
https://workdrive.zohoexternal.com/external/27a063dd02e4c3c082eebaf0b34f84f30b388d64af00c126faa08bc2492cede7

Regards

Hello Tejendra,

It looks like the gate drive is not working adequately, are you sure the device is not damaged, have you got the same behavior on additional boards?  If not, suggest swapping out the device.  Clearly there is something going on with your gate drive.  Look at the Boot diode, suggest using a UF, or Schottky diode with low reverse leakage current, look at the EVM and pick something similar to this.  Make sure rated to Vin max.  

Hope this helps,

David.

Hi David, 
I Have attached one more Picture of the HO1 Signal Please check with this. This is a probe issue sorry for that. Please consider the Blue Signal in the link attached. Please ignore Yellow. 
Here is the diode part number PMEG6002EJ,115 Nexperia

Inductor Part number - SER1052-152MLC
Mosfet Part Number - RS6L090BGTB1

https://workdrive.zohoexternal.com/external/da182546116fd63f6f880110e919df5b6b100fef2e0d4d6da180040e42fd5d35
Regards