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LM5156H: - Slope compensation fail to adjust

KEI SHUN LEE
Prodigy 10 points
Part Number: LM5156H
Other Parts Discussed in Thread: LM5156, , LM5155, LM5155EVM-BST

Hello Sir / Madam, 

I need a DC-DC booster for cooling Fan loading in EMI dummy load box. 

I have 54V cooling fan and the AC - DC power supply with 12V output. 

so, I want to design a DC DC booster from 12V input and 52V output ~ 3A. 

A testing PCB is made, the DC DC booster can output 52Vdc. However, the max loading is 0.7Adc. 

The circuit have sub-harmonic oscillation, when this output load is higher than 0.7A 

(Yellow line = Vout, Green line = inductor current, Blue line = COMP volt, purple line = gate voltage) 

the switching is normal, if the loading is 0.69A 

https://1drv.ms/u/s!ApYUhFZeSAGfsgLSfYJUytsSVu3v?e=OwARQy

The circuit have sub-harmonic oscillation at loading 0.7A 

https://1drv.ms/u/s!ApYUhFZeSAGfsgHxy5DfhXAH14iB?e=C9NRTc

And this is the SHC 

https://1drv.ms/u/s!ApYUhFZeSAGfsgNdrXJOC5j7Ab3B?e=yLnhpS

https://1drv.ms/u/s!ApYUhFZeSAGfsgSop-Sbl39k_oQt?e=Of1zi8

Design parameter

Vin = 12.5V Lin ~ 14.2A 

Vout = 52V ~ 3A 

Fsw = 416Khz 

L = 54uH 

crossFreq is 75.9KHz, phase margin is -90 degree 

Slope compensation - low pass filter 0ohm and no capacitor ( since the low pass filter made the ramp delay, it is no work for loading larger 0.14A ) 

it seem the the slope compensation is not effective. The result is similar, if R6's value from 100 to 825 ohm. 

This is no use, when larger value of inductor- L1 (100uH and 16uH also tested) or lower current sense resistor - R17 

Do you have any suggested to made it stable? 

Thanks and regards 

KS 

 

  • 0
    TI__Guru 58581 points

    Hi Kei Shun Lee,

    thank you for using the E2E forum.

    Have you already used the Quickstart calculator for your design.

    You can find this on the product page for the LM5156 (unfortunately it is not linked on the LM5156H page so far)

    LM5156 data sheet, product information and support | TI.com

    Best regards, 

     Stefan

  • 0 in reply to Stefan Schauer
    TI__Guru 58581 points

    Hi Kei Shun Lee,

    I have not seen an update on this thread for the last 11 days.
    If the issue is solved it would be great to press the is solved button.
    If there is still something open, just let me know with the new details.
    Best regards,

    Stefan

  • 0
    Prodigy 10 points

    Thanks Stefan Schauer! 

    I may find the solution, 
    At the beginning, I test my own PCB BRD and get the value from  following by the file from TI (LM5155_56_Quickstart_Calculator_for_Boost_Converter_Design_V1_1_1). 

    The MAX loading is 52V @ 1.4A, However, my target is 3A MAX. 

    I get the LM5155EVM-BST and test again. The test can be drawn at 52V@2A in normal. 

    So, I will take a look of my layout, and sorry I can't upload any waveform for your reference. 

    Best regards 

    KS 

  • 0 in reply to KEI SHUN LEE
    TI__Guru 58581 points

    Hi Kei Shun Lee,

     

    I have not seen an update on this thread for the last 23 days.

    Maybe you could solve this issue already in the meantime, in this case it would be great to press the is solved button.

    If there is still something open, just let me know with the new details.

    Best regards,

     

    Stefan