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LM3488: How to meet output 5V, 5A

Tseng Ruihong
Prodigy 100 points
Part Number: LM3488
Other Parts Discussed in Thread: LM25117

Hi Sir

This is our main power circuit. The LM3488 does not meet reference design 5V,10A output, and our design target is 5V, 5A.

Due to my power supply capacity, the E load set at 1.5A. The current load and voltage position are set on C432 .

All of input is 1.5A current load, the variable is input level 6V, 10V, 12V and observes C432 output  voltage. We also short the R422.

  1. 6V input, 5V output is OK
  2. 10V input, 5V output drop.
  3. 16V input, 5V output drop.

Please help us to find out the output drop issue.

MAIN_POWER.pdfLM3488_WBDesign.pdf

  • 0
    TI__Mastermind 31015 points

    Hi Tseng,

    Sorry to hear you are having trouble. I would not advise shorting R422, since the current sense resistor plays a role in overall power supply stability. 

    Additionally, may I have misunderstood something? Your yellow waveforms don't all seem to correspond to the input voltage that you say. I might be missing where the ground reference for all the channels are.  

    Can you retake the waveforms at VCC_3.8V node where VIN = 6V, 10V, and 12V and provide several cycles (3-4) of SW node, ISEN and COMP of LM3488?

    Thanks,

    Richard

  • 0 in reply to Richard Fu22
    Prodigy 100 points

    Hello Richard

    I am very appreciated your suggestion, it is very powerful.

    The R422 is recover, but the value is 25m. It is much better before, but it still can not meet 5V, 5A.

    The test result as attach.1057.LM3488.rar

  • 0 in reply to Tseng Ruihong
    TI__Mastermind 31015 points

    Hi Tseng,

    Thank you for sharing the waveforms. It looks like this may be an issue with the converter upstream of the LM3488, in that in slide 1, the bottom-most left slide, VCC_3.8 is shown to be 200mV. Based on the schematic given, it looks like LM3488 is much below bias operating region, which has to be at least 2.97V. 

    Can you confirm the operation of the LM25117 first under all expected operating conditions by disconnecting the LM3488, and seeing if it'll work? 

    Thanks,

    Richard

  • 0 in reply to Richard Fu22
    Prodigy 100 points

    Hi Richard

    You are right, we have found the problem from LM25117. We are trying to meet reference design spec on LM25117, Vout p-p: 9.615mV. 

    So, I should be create new problem or still on this page?

    Summary, the Cout is a control variable, from 100u, qty4, 200u, qty3,4, etc, all of the ripple are observed from 30mV to 40mV, when Eload is 5.5A.

    My question is, reference design Vout p-p: 9.615mV is 15A, 3.79V output? Also, we have ask TI taiwan to support us demo board to verify LM25117. 

    The order number is T00797419.LM25117.rar

  • 0 in reply to Tseng Ruihong
    TI__Mastermind 31015 points

    Hi Tseng,

    I would recommend closing this thread and setting up a new one specifically for the LM25117. If you are still having issues after solving the current one with the LM25117, you can reopen this thread or set up a new one. 

    Thanks,

    Richard

  • 0 in reply to Richard Fu22
    Prodigy 100 points

    Hi Richard

    It is a pity, you doesn't solve LM3488 problem. Form report 3.8V input(slide 6) has showed my LM3488 circuit has a design problem, 3.8V input test is block LM325117. 

    Also, it seen found the LM3488 problem, but not your suggestion.however it need some component to verify. 

  • 0 in reply to Tseng Ruihong
    Prodigy 100 points

    Hi Richard

    I solved the problem. so close this issue