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Original question:

TPS2121: Thermal event failure

TPS2121: Part burning up under normal working conditions

Nir Dvash1
Intellectual 470 points
Part Number: TPS2121

Dear Sirs,

We have the TPS2121 designed into our product. Please take a look at the attached schematics. 

Our max. input voltage is 17V and our maximum current consumption out of the device is 3.5A

In two case when power was applied to the IN1 input, the device immediately caught fire. On the other

hand, we have tested around 30 units of our product (Same exact design and production run) and they

are all working fine.

We are troubled and puzzled by this and since we have read other cases which sound the same we 

are worried that something is wrong with the device itself.

We would be grateful to hear back from you,

Nir.


1856.TPS2121.pdf

  • 0
    TI__Genius 13260 points

    Hello Nir,

    Have you tried placing a known working device onto the failed board to see if it also gets damaged? 

    What is the total load capacitance during turn-on?

    Were you able to gather any scope shots including input/output voltage, output current and ST?

    Can you also provide a picture of the damaged device?

    Regards,

    Kalin Burnside

  • 0 in reply to Kalin Burnside
    Intellectual 470 points

    Hello Kalin,

    Please see below a close up image of the burned IC (U25) and its surroundings.

    I think that the burn also destroyed the PCB below it so there is no way to place a new deice on this board.

    As for the total load capacitance, as you can see from the schematics there are only a few capacitors

    at the output of the TPS2121 ranging just a few uF each.

    I was not able to gather any scope shots since this happened very fast. I can tell you that I have

    verified the correct functionality of this design on other boards, measuring correct input/output voltages and correct ST output.

    Again, we have around 30-40 boards that work but have a few that don't and in which the TPS2121 fired up as soon as power was applied.

    Any ideas what might be causing this?

    Nir.

  • 0 in reply to Nir Dvash1
    Prodigy 100 points

    I think I had the same problem. See 10.7 of the datasheet and try adding something like SMAJ17A between IN1 and/or IN2 to ground. Also try adding another NSR20F30NXT5G from TPS2121 output to ground for reverse polarity protection. These solved my problems. I burned up quite a few boards before getting it right.

    Now, if only someone could ship us some more parts!

  • 0 in reply to Nir Dvash1
    TI__Genius 13260 points

    Hello Nir,

    Since the schematic looks fine, there can be a few explanations for this. Since this was during turn-on and only happened in 2 out of 30 boards (assuming same setup) it's possible you accidentally swapped power and ground for those two tests which could definitely explain the damage.

    Also, if there was enough of a transient (long cables for test setup) that could damage the internal ESD diode it would have a direct path to ground through the device causing it to quickly burn up. As Randy said, section 10.7 in the datasheet will go over methods to help prevent this from occurring. 

    Regards,

    Kalin Burnside

  • 0 in reply to Kalin Burnside
    Intellectual 470 points

    Thank you Randy for sharing this info. 

    Kalin  - Since the power input to the TPS2121 is a USB type C connector this eliminates the possibly of swapped power and GND. However, we do have a very long cable (3 meters) from the power supply output to our unit's input and so the transient issue seems to be the problem!

    Thank you for your help!

    Nir