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TPS25947: EFuse does not reliably switch on

Timo Novak
Prodigy 10 points
Part Number: TPS25947

Tool/software:

Hi there!

We are using TPS259470LRPW eFuse to switch on and off a resistor.

When the EN/UVLO pin is rising from 0V to 3.3V, the voltage at the OUT should be the same as IN, i.e. 12V. Sometimes, the voltage at OUT is too low, i.e. 2V or 6V or 10V. In the oscilloscope you can see the EN/UVLO in green and OUT in yellow.

See the attached images. 

The effect occurs in room temperature sometimes. When cooling down the assembly, I can provoke the behavior. 

Has anyone ever seen this behavior? We are using the same type of EFuse in other boards, there they work reliably. Could it be that there is a bad batch? The text on the chip is 2A8H 518 C497.

Thanks for your help!

  • 0
    TI__Mastermind 38835 points

    Hi Timo,

    Can you share your schematic and test conditions (load details and test performed before this). You mentioned cooling the board is causing this. Can you tell more details. Is this happening with multiple devices or multiple boards? Did you perform A-B-A swap?

    Best Regards,
    Arush

  • 0 in reply to Arush Gupta
    Prodigy 10 points

    Hi Arush,

    thanks for you quick reply.

    See the attached schematic. There are multiple of these on the board. I noticed the behavior on all of them. This occurs sometimes at room temperature, but I can provoke it when cooling with cooling spray, then it happens every time. The warmer the board gets the more reliably it seems to get. I tested with multiple assemblies, it happens on all of them. The load is a 36 Ohm resistor (no capacity or inductance) and an LED with resistor to show the status, leading to a power of 4 W.

    We are using the same eFuse on other boards, there they seem to work reliably under the same test conditions. Other boards have a different number engraved on the chips.

    Best, 

    Timo

  • +1 in reply to Timo Novak
    TI__Mastermind 38835 points

    Hi Timo,

    Timo Novak said:

    We are using the same eFuse on other boards, there they seem to work reliably under the same test conditions. Other boards have a different number engraved on the chips.

    Any moisture buildup when you are using cooling spray. This can create some leakage paths which can result in unexpected behavior like what you are seeing. (Vout varying). Does this problem go away when you replace the device or resolder the same device or is it happening on same board with different devices also.

    Also, can you share the symbol marking. I can check and tell you if this is correct marking or not. 

    This behavior which reported is not expected and is not seen when we did the cold temperature testing. We usually use Themestream or thermal chamber, so moisture is not an issue in our setup. 

    Best Regards,
    Arush

  • 0 in reply to Arush Gupta
    Prodigy 10 points

    Hi Arush,

    Yes I think that might be it. The initial problem wasn't caused by the eFuse. I will come back to you if anything changes.

    Thank you very much for your support.