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TPS23861: Some IC did not work anymore after a few days in the field

user3885262
Prodigy 100 points
Part Number: TPS23861

Hi 

We use the TPS23861 in our 4G router to power a small video camera.

Our schematic are attached below:

We used the reference design.

All works very well, we have now 50 devices in the field. 

But 2-3 devices we get back because the PoE part is broken.

I took of the TPS IC and soldered in a new one and everything worked fine again.

I think the whole IC is broken, but why? For a short test we soldered the borken IC on EVALUATION BOARD TPS23861EVM-612 and checked with the sotfware the status of the IC but there is no answer/connection to the device...

Schema_PoE_CK5_MainPoE_V2.0.pdfSchema_Power_CK5_MainPoE_V2.0.pdf

  • 0
    TI__Mastermind 40100 points

    Hi User,

    Can you help double check the VPWR and VDD startup sequence? For the TPS23861 the VPWR rail must go up first before VDD goes up. Looking at the schematic I don't see the LDO is able to do this. Perhaps with a divider on CE pin, you can turn ON the LDO after the VDD goes above its UVLO. Thanks!

  • 0 in reply to Darwin Fernandez
    Prodigy 100 points

    Hi Darwin

    thanks for your fast answer :-)

    Yes you are right, maybe the LDO turns on faster than VPWR. But can this damage the IC?

    So we will change to this:

    Turn on LDO sourced by VPWR and delayed on the CE pin with rc.

    OK?

    We are anyway out of pcbs and had to order new ones....

    Shoutdown is also critical? VPWR is longer present than VDD or vice versa..

  • 0 in reply to user3885262
    TI__Mastermind 40100 points

    Hi User,

    Yes it can damage the IC if the proper startup sequence is not met. Delaying the 3.3V enable would be okay as long as the delay is long enough to stay LOW while VPWR goes above its UVLO.

    Shutdown is not critical. Thanks!