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LMZ10504: the output pin shortcircuit

user1359349
Intellectual 430 points
Part Number: LMZ10504
Other Parts Discussed in Thread: LMZ31704, LM10504, TPS25925, TPD1E05U06

when i use the LMZ10504，this module often damaged,the ouput pin has shorted to ground,

the input voltage is 4.5 and the output is 3V3.

please see the schematic and pcb figure.

on the power board,the 48V--5V power module output 5.5V to the blackplane,so there is a oring diode one he board,(the two power board will insert on the shelf)

then ,the5.5V from the blackplane is supply for LMZ10504

please help me,what had happend on the LMZ10504,thanks.

  • 0
    TI__Intellectual 1155 points

    Hi user 1359349,

    there are some question that would help me in supporting you:

    - Was the part powered up and the failure occurred after running for some time? Or did you find the Vout short to GND before the device was powered up (time zero failure)?
    - I see in your schematic that you use three 22uF/100V output caps (C69, C70, C71). Can you provide me the part number and/or at least the ESR of the capacitors?
    - How and where is the Fbb resistor tied to GND? Is the trace on the other side of the PCB? I can't find it on the image you provided. The connection between FB pin, Fbb resistor and GND should be kept as short as possible.

    Thanks for your answers and best regards,
    Michael

  • 0 in reply to Michael Daimer
    Intellectual 430 points

    hi micheal

       i'm sorry for this delay,because i don't know what time this failure occurred ,so this week i try to damage the moudle

    the first question

    if the input power supply is 5.5--7V,the module work is ok,even turn on and turn off the power supply exceed one thousand times;

    if the input power supply above 7V,the module work is ok,but the surface temperature is very high,turn on and turn off the module exceed thousand times ,the module is ok

    but if the input ower above 8V,when turn on and turn off the input about ten times ,the ouput was shortcircuit to ground,

    the second question

    there is a mistake on the schematic ,the capacitor on the output is 22uF/25V ceramic capacitor ,the ESR is very low

    the third question

    the feedback resistor was on the bottom side ,under the module ,the trace is very short

    the attached was the test enviroment 

  • 0 in reply to Michael Daimer
    Intellectual 430 points
    by the way ,the board need hot plug ,the input have no hot plug chip and TVS,only have one Oring diode,thanks
  • 0 in reply to user1359349
    TI__Intellectual 1155 points

    Hi Qiang,

    you wrote that your input voltage goes up to 8V. Then the device gets destroyed.

    The absolute maximum rating for the input voltage is 6.0V, the maximum recommended operation input voltage is 5.5V (see datasheet LMZ10504 on page 4).

    Stressing the device beyond abs max ratings will cause damage to the device. I guess that both internal FETs are blown and that's why your Vout is shorted to GND.

    Also hot plugging is critical, when your maximum allowed input voltage written in the datasheet and your actual input voltage are close. Hot plugging can cause voltage spikes of some volts, which can also overstress the part. Functionality is not guaranteed any more because of violating the abs max ratings.

    For 8V of input voltage, I recommend to use LMZ31704. It is rated up to 17V of input voltage and can also deliver 4A of output current. The case size is pretty much the same as for the LMZ10504.

    Best regards,

    Michael

  • 0 in reply to Michael Daimer
    Intellectual 430 points

    hi michael

      thanks for your help,for find out the reason of the output short circuit, i have inceased the input voltage ,but actually ,the input only 4.1---4.5V

    this test proved that  this issue maybe caused by   surge of  input ,so ,i add a TVS  on the input .

    i hope the TVS can absorb the surge voltage,do you agree with me? is the ture of the problem?and is the solution to solve the problem?

    in addition,because the LM31704 is not pin to pin compatible to LM10504,so i can't replace it direct.

     

  • 0 in reply to user1359349
    TI__Intellectual 1155 points
    Hi Qiang,

    depending on your description, I agree that the hot plugging is most likely the cause of the issue.
    First I got it wrong and didn't understand that your high input voltages only were applied for testing. But this proves in my opinion that you need input protection. Try a suitable TVS. Perhaps TPD1E05U06 is a possible candidate, but have a detailed look in the datasheet, if it fits for your application. For more protection features you can think about using an e-fuse, like TPS25925.
    Nevertheless, if the issue still occurs with a proper input protection, please don't hesitate to contact us again. Please let me also know, if the protection works.

    Best regards,
    Michael
  • 0 in reply to Michael Daimer
    Intellectual 430 points

    hi  Michael

       i will try it as your advice,thank you very much!