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TPS56339: Device has either popped or set on fire when Vin (24V) has shorted to Ground

Euan Clapworthy
Prodigy 80 points
Part Number: TPS56339

I am using the TPS56339DDCR buck converter in a custom circuit. For the circuit design I have used a reference design from WeBench Power Designer. An image of the circuit design is attached.

I have tried to follow the recommended circuit layout as closely as possible.

In the occasion of short circuit failure, several of the buck converters have been destroyed and one even had a small electrical fire. The reason so many shrts occured is because we are trialling a modular board-to-board connection system which still has a few kinks to iron out.

I have attached a picture of the aftermath of one of these failures.

So far the only solution I've been able to come up with is to add a resettable fuse to the input of the device, but if you could indicate any methods to provide additional safety measures it would be appreciated.

On a side note, the inductor is making an audible humming/buzzing sound. Is this something to do with the switching frequency of the device?

Thank You

  • 0
    TI__Genius 9530 points

    Hi，

    This part integrates output undervoltage protection. When the regulated output voltage is lower than 62.5% of the nominal voltage due to over current triggered, the undervoltage comparator is activated. 120 μs deglitch timer later, both the high-side and low-side MOSFET turn off, the device steps into hiccup mode. So normally it won't damage IC when short test, you can refer the figure 32/33 in datasheet page 21. 

    So for better analysis, some other information needs your help . 

    1. What's the failure performance ? It would be better if you could provide some failure waveform for analysis. 

    2. For inductor , what's the part number or please check its frequency , Irms/Isat .

    BRs,

    Young

  • 0 in reply to Young Zhao
    Prodigy 80 points

    Hi,

    Thank you for your fast reply. See answers to your questions below:

    1. Unfortunately we do not have an oscilloscope at the moment so I have no way of analysing the failure performance. Is there anything else I can do to assess or are we stuck without an oscilloscope?

    2. I have tried 2 separate inductors.

    • SRP6540-5R6M: Frequency < TPS56339. Inductor hums when circuit is pulling maximum current/power
    • XAL6060-562MEB: Frequency > TPS56339. Inductor hums when circuit is drawing no current/power
  • 0 in reply to Euan Clapworthy
    TI__Genius 9530 points

    Hi ,

    sorry to confirm the short test again, this short test  is SW shorted to GND or VIN shorted to GND ?

    and what's the VIN and Iout ?

    BRs,

    Young

  • 0 in reply to Young Zhao
    Prodigy 80 points

    Hi,

    The short was on the input to the device so between VIN and GND.

    VIN = 24V. 

    Iout = 2.56 A but the circuit is designed to support Iout = 3A

  • 0 in reply to Euan Clapworthy
    TI__Genius 9530 points

    Hi,

    thanks a lot for your confirm. 

    It should trigger VIN UVLO when short test , and shut down device in theory. 

    Could you share the schmatic and layout to us ? and what's the failure rate by short test ?

    BRs,

    Young

  • 0 in reply to Young Zhao
    Prodigy 80 points

    Hi,

    Schematic and layout are below.

    Values for schematic:

    • Cin1 = 10uF
    • Cin2 = 10uF
    • Cinx = 100nF
    • Rbst = 30 ohm
    • Cbst = 100nF
    • L1 = 5.6uH
    • Rfbt = 52.3 kohm
    • Rfbb = 10 kohm
    • Cout = 22uF

  • 0 in reply to Euan Clapworthy
    Prodigy 80 points

    Not sure the images were uploaded properly there, so I've reattached them.

  • 0 in reply to Euan Clapworthy
    Prodigy 80 points

    Hi,

    I think I have figured it out.

    After trying to recreate the short circuit fault, I realised that shorting VIN to GND would not destroy the chip.

    Then I noticed that there are some magnets that are screwed onto the board that have rubbed off some of the soldermask which could potentially short my +24V input to the +5V output from the converter. I think this is what destroyed the device.

  • 0 in reply to Euan Clapworthy
    TI__Genius 14455 points

    Hi Euan

         Glad to hear that you were able to identify the issue. We will go ahead and close this post. If you need further assistance on this issue, please feel free to open it again.

    regards,

    Gerold

  • 0 in reply to Euan Clapworthy
    TI__Genius 9530 points

    Hi,

    Great to hear this issue was fixed . Please let us know if you have any other question . Thanks .

    And based on our previous short test on TPS56339, IC may damage only happened when SW short to VIN .

    BRs,

    Young

  • 0 in reply to Young Zhao
    Prodigy 80 points

    Hi,

    There was one other problem that I had with this converter.

    When the maximum power was being drawn from the circuit, the inductor was producing an audible humming noise.

    I think it is because the frequency of the inductor is less than that of the buck converter, but could you advise on how to get rid of this sound.

    I have also tried an inductor with a frequency greater than the buck converter, and that produced a humming sound when the circuit was on but drawing no power/current.


    Thanks

  • 0 in reply to Euan Clapworthy
    TI__Genius 9530 points

    Hi,

    The devices will work in ECO mode with lower frequency at light load.

    The audible noise occurs from inductor or capacitor when frequency < 20KHz at light loading. And this is common .  You can try the distributed airgap inductors.  Also you can RTV the coil or varnish.

    Is the light load the typical application condition ? and how the max loading now ? any noise at max loading ?

    BRs,

    Young

  • 0 in reply to Young Zhao
    Prodigy 80 points

    Hi,

    The noise tends to occur closer to maximum loading, but the circuit can be at light loading sometimes as well. It is being used in a dynamic LED display so the maximum current pull depends on the animation running on the LEDs.

    I have tried 3 of the recommended inductors on WeBENCH and they all make the humming sound

  • 0 in reply to Euan Clapworthy
    TI__Genius 9530 points

    Hi，

    Could you help share the load transient waveform for us ? Vout ac voltage .

    BRs,

    Young