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LMX9838 Power-up problem

Mike Frampton
Prodigy 30 points

Hello,

I am trying to debug an issue with an LMX9838 module I am trying to integrate into my product.

The problem I'm seeing is that the module will only power-up intermittently. According to the datasheet, after applying 3.3 V to the module's supply I would expect the Tx line to go high after some time. However, I don't see the Tx line go high.

I can fix the problem by applying 3.3 V from a bench power supply. I find that after I have powered it up once from the bench supply then I can successfully power the module up normally on my board. I suspect this is a problem with the power supply I'm using to drive the module. The regulator I'm using to power the module is the TLV70233.

Cheers,

--Mike

  • 0
    TI__Guru* 85400 points
    Hi,

    Please feel free to contact Lin, Ryan at ryanlin@ti.com directly.

    Regards,
    Gigi Joseph.
  • 0 in reply to Joseph Gigi
    Prodigy 30 points

    Hi Gigi,


    I have not been able to contact Ryan, emails sent to him seem to bounce back.



    Delivery to the following recipient failed permanently:

         ryanlin@ti.com

    Technical details of permanent failure:
    Google tried to deliver your message, but it was rejected by the server for the recipient domain ti.com by cluster5.us.messagelabs.com. [216.82.250.83].

  • 0 in reply to Mike Frampton
    TI__Guru* 85400 points
    Hi,

    Apologise the inconvenience. Let me check internally about this and get back to you.

    Regards,
    Gigi Joseph.
  • 0 in reply to Joseph Gigi
    TI__Expert 4085 points

    Hi Mike,

    I will help you out with this. Did you make any progress on this so far?

    Could you please provide me your schematic and layout?

    Thanks,

    Julian

  • 0 in reply to Julian Di Matteo
    Prodigy 30 points

    Hi Julian,


    I believe I have rectified the problem. I have attached a document containing my original schematic.

    I solved the problem by changing the regulator on my board to a TLV70233, which has a higher current output than the regulator shown in the schematic. Also, the first time I powered up my board I had to use a bench power supply rather than the USB supply used during normal operation.

    I found this problem rather annoying because the LMX9838 datasheet doesn't say anything about current draw during startup. Hopefully this info will be helpful for somebody else.

    Thanks,

    --Mike

    WTTR2-Bluetooth.pdf

  • 0 in reply to Mike Frampton
    TI__Expert 4085 points

    Hi Mike,

    I'm glad you were able to resolve the issue. Thanks for the feedback and let me know if you have any other questions.

    Best Regards,

    Julian

  • 0 in reply to Julian Di Matteo
    Intellectual 700 points

    Just want to add some info regarding this.

    We have been using this LMX9838 for a few years without problems. This spring, 80% of the pcbs failed with this components in a batch of 20 pcbs. The failure was two different kinds. Either internal shortcut or no current at all. I suspected overheat and issues with the manufacturer so i ordered new ones and manually changed them. The same result persisted, about 80% of the new ones failed as well. In this time we just gave up and had to remain without blutooth on this small prototype batch.

    As it happend later I checked where we purchased those bluetooth chips, it turns out that the manufacturer and us ordered from the same place. I ordered, as a test, a few from another place and tried them. Wolalala, they all worked like a charm, like it allways did before on the same pcbs as earlier had failed bluetooth chips.

    This has costed us huge amounts of money and time to investigate, so I want to spare others with the same issues. If you have the same issues, try and source them from another place.

    (There is at least one bad batch out there, TI. If you email me I can tell you more about where we ordered and where they failed - to not hang out any distributor in the forum.)

    Br,

    Mikael