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TPS61046: Not Switching

Jerker Skogby17
Prodigy 120 points
Part Number: TPS61046

We have already successfully assembled and tested 500+ PCBs containing the TPS61046 together with a professional SMT House. 

The design itself seems to be fine since we have not had any issues at all until now.

But for the next batch of 300 PCBs roughly 50% of the TPS61046 do not switch. 

We find this a bit odd since nothing in the SMT process has been changed, nor any components. 

The output voltage from the circuit is roughly Vin - 0.7V when the Enable pin is High (2.5V).

We have measured on the SW pin and it is not switching as compared to the working units. 

We thought the problem might have been due to oxidation on the PCB, however using a lot of soldering flux and re-attaching the same IC does not work.

Replacing the TPS61046 with a new one on the same PCB does however solve the issue.

Do you have any idea what might have happened, what could have caused this problem?

It should be added that the TPS61046 is from the same batch as we used the last time and that it was about 4 months since the last SMD process.

  • 0
    TI__Mastermind 46905 points
    it look like IC is damage from your description and experiment. to confirm this, try these experiment
    1. make the voltage at each pins of a failure device with EN=H and L
    2. remove the external components connected with the TPS61046, measure the impedance between each pin and the ground pin. and then measure the ESD diode between GND pin to other pin to check if connection of the pin is good.
    3. careful check if there is physical damage in the IC.
  • 0 in reply to Jasper Li
    Prodigy 120 points
    Thank you for your feedback Jasper!

    Regarding Step 2, what impedance should we expect when measuring the impedance between the pins and ground?

    When storing the TPS61046 before it is mounted, should it be protected against something else than ESD? Humidity etc?

    Thanks again!
  • 0 in reply to Jerker Skogby17
    TI__Mastermind 46905 points
    no exact data, but i would expect it is should be high impedance, higher than 100Kohm. you can compare the fail device with the normal device.
    humidity within 30% to 70% should be OK.
  • 0 in reply to Jasper Li
    Prodigy 120 points

    Hi again Jasper,

    We have measured the impedance on all of the pins from one of the faulty units towards ground. Both on ones mounted on PCB (with external components removed) and by de-soldering a non functional TPS61046 and measuring direct on the pins. We then compared it to a functional TPS61046.

    The conclusion is that there is no remarkable difference on any of the pins. 
    All pins show an impedance of >1MOhm and the impedance is roughly the same between the 2 non-functional and the 2 functional units we measured on. 

    Right now we are at a complete loss of what the fault may be... 
    We have not changed the design, no components and there is basically no load on the TPS61046 when we test them the first time. 
    We have X-rayed some of the units and the connection to the PCB looks good. 

    Do you have any other ideas of what might have happened?

  • 0 in reply to Jerker Skogby17
    TI__Mastermind 46905 points
    could you contact the local TI quality engineer or field support engineer to do fail analysis for this device?
  • 0 in reply to Jasper Li
    Prodigy 120 points
    Thanks Jasper, I did, they will get back to me on Thursday.

    While I wait for a TI field support engineer, could you please tell me if the IC is marked in any way for traceability like batch info or similar so that we can compare if the faulty ones are from the same batch as the previous ones?
  • 0 in reply to Jerker Skogby17
    TI__Mastermind 46905 points
    There is marking on the top of the device. it should be 7 characters marking.
  • 0 in reply to Jasper Li
    Prodigy 120 points

    Is the marking the same on all devices or rather; which number will be different if the devices are from different batches?