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TPS62180: The 2nd and later PCBA of TPS62180 are not as good as the 1st PCBA

wallace liu
Intellectual 280 points
Part Number: TPS62180
Other Parts Discussed in Thread: TPS53515, TPS54824

Hi Expert,

A TPS62180 is used to convert 12V to 5.55V.

A few PCBA were fabricated at different time against the same schematic diagram, the same PCB layout and  the same peripheral components. However, only the PCBA made at the 1st time succeeds. It converts the voltage with an input power of 22.2W at an efficient of 91%。

The rest PCBA either cannot deliver 3.6A, or work at a low efficiency of 63%.

The only schematic diagram is display below.

The only PCB Layout is shown below.

The same PCBA is here

Do you have any clue which results the circuit deficiency? Or, do you have any suggestion on circuit debug?

Thank you in advance!

Wallace

  • 0
    TI__Mastermind 18510 points

    Hi,

    Seems the schematic and layout are not uploaded successfully, please re-upload.

    From your description, the rest ones can't work with 3.6A loading, but the first version can output 4A*5.55~=22w, so seems the rest ones worked abnormally, not only lower efficiency.

    And If same PCB layout, same schematic, same test equipment, just different PCBA, I suppose maybe some components are different between the first board building and the subsequent ones, which cause the circuit work abnormally.

    Suggest you do some waveform comparison between good board and abnormal board,  Vin/Vsw/Vout. And also you can do component ABA comparison between good board and abnormal board. you can change the IC first and then others, to check whether the issue is following some component.

    Yuchang

  • 0 in reply to Yuchang Zhang
    Intellectual 280 points

    Hi Yuchang，

    Thank you for you quick response.

    PCBA #1, Input 12V/1.85A, Output:5.5V@1.5Ω，efficiency= 91%

    PCBA #2 Input 12V cannot deliver 5.5V to a load of 1.5Ω,(causing a current limitation on 12V input power supplier )

    PCBA #3, Input 12V/2.6A, Output:5.47V@1.5Ω，efficiency= 63%, 

    I am reloading those figures and hope they would be loaded successfully.

    BTW, does "ABA(component ABA comparison)" stand for?

    Wallace

  • 0 in reply to wallace liu
    TI__Genius 14455 points

    Hi Wallace

      The images still did not come through. If yuo drag and drop the images, it can have issues. You will have click Insert and then select the image to insert it into the post.

    Regards,

    Gerold

  • 0 in reply to Gerold Dhanabalan - Online Design Tools
    TI__Mastermind 35185 points

    Hi Wallace,

    I can see the images now.

    An ABA swap is to swap the TPS62180 on PCBA #1 with the one on PCBA #2. If PCBA #1 now has the issue, it suggest the problem is related to the IC that was on PCBA #2. If PCBA #2 still has the issue, it suggest there is some other problem with PCBA #2.

    If both boards now work, it suggest there may have been an assembly issue that was fixed by re soldering the device. To rule this out, the ICs on PCBA #1 and PCBA #2 should be swapped again. If the issue appears again on PCBA #2 with the original component back on it, it suggest there is something marginal in the design that is causing some boards to have this issue.

    It would be good to try an ABA swap of the output filter LC components to see if it is related to them.

    One comment I have on the PCB layout is the input cap placement is not ideal. The input caps should be placed across the pins of the IC with the SW nodes routed below them. One cap should be very close to pins A1 and A3 and the other close to pins F1 and F3. Please see Page 31 of the datasheet.

  • 0 in reply to Anthony F
    Intellectual 280 points

    Hi Anthony,

    Thank you very much for your patient explanation on detail.

    Actually, the weird abnormal IC performance across a few PCBs happens not restrictly to TPS62180 only. Neither TPS53515 nor TPS54824 perform normally on PCB other than PCB #1. Here is a summary.

    TPS62180@

    PCBA #1: Output 5.51V@1.5Ω; Input: 12V/1.854A; Efficiency=91% 

    PCBA #2: The input 12V power suppler was forced to enter Constant Current Mode to limit its power output, when a 1.5Ω load is connect to TPS62180.

    PCBA #3: The input 12V power suppler enters Constant Current Mode with 1.5Ω

    PCBA #4: Output 5.47V@1.5Ω; Input: 12V/2.6A; Efficiency=63%

    TPS54824@

    PCBA #1: Output 3.75V@0.5Ω; Input: 12V/2.5A; Efficiency=93.7% 

    PCBA #2: Output 2.47V@0.5Ω; Input: 12V/1.6A; Efficiency=63%

    PCBA #3: The input 12V power suppler enters Constant Current Mode with 0.5Ω

    PCBA #4: The input 12V power suppler enters Constant Current Mode with 0.5Ω

    TPS53515@

    PCBA #1: Output 2.3V@0.3Ω; Input: 12V/1.56A; Efficiency=94% 

    PCBA #2: The input 12V power suppler enters Constant Current Mode with 0.3Ω

    PCBA #3: The input 12V power suppler enters Constant Current Mode with 0.3Ω

    PCBA #4: The input 12V power suppler enters Constant Current Mode with 0.3Ω

    I am going to start circuit debug with waveform measurement and capacitor/ inductor swap.

    This swap of IC seem difficult to me, because of their BGA footprint.

    Wallace

     

     

  • 0 in reply to wallace liu
    TI__Mastermind 35185 points

    Hi Wallace,

    Is the same input power supply being used for all of these tests? It seems like any of the regulators can put this into constant current mode. This makes me think it is somehow related to the input instead of the individual regulators.

    Before swapping components, is it possible to disable all of the power supplies then enable them one at a time to see if it is related primarily to only one converter?

  • 0 in reply to Anthony F
    Intellectual 280 points

    Hi Anthony,

    Thank you for your following questions。

    The desktop DC power supplier is used to feed these DC-DC convertors with DC12V at the same time through fuses. 

    One specific high power resistors is connected to related DC-DC convertor in one test, while the rest DC-DC convertors are open-loaded. 

    To watch and compare the waveform of  input/output-pin and SW-pin seems a good idea, which was suggested by Yuchang. I am going to have eyes on it.

    Thank you!

    Wallace