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TPS78233 creating noise when powering Atmega256RFR2 WiFi audio chip

Kayiita Johnson
Prodigy 415 points

Hey all,

When my customer tries to turn on their WiFi chip through the TPS78233, there are a couple issues.

1, it creates a lot of noise; and 2, it results in much less of a range for the WiFi chip. 

When they replace our part with the Maxim part # MAX8891EXK33 it works just fine.

Any thoughts on why this is?

Here are some additional details:

There is a 4.1mA draw without the WiFi chip being on. Once on, it rises to 10mA, with 14mA on receive and 18mA on transmit.

Their products are already in the field, so time is of the essence. I have the gerbers as well if needed (directed towards TI folks).

Thanks,

Kayiita

  • 0
    TI__Genius 10405 points

    Possible missing ground connection on pin 4 of  customer design.

     

    Recommend checking with customer to try a white wire rework and test.

     

      - Rick

  • 0 in reply to Rick Nardone
    TI__Genius 10405 points

    Customer says U2 p2 and U2 p4 are both grounded, so the device is connected properly.

    Problem still open.

     

    - Rick

  • 0 in reply to Rick Nardone
    TI__Expert 8905 points

    Hi Kayiita,

    Could you describe more about the noise - namely is it noise that is coupling through the device? It would be great if you could provide a scope shot of Vin and Vout as well, for a quick check of the noise.

    The MAX8891 has a much higher PSRR but a much higher Iq, so I suspect it may be input noise coupling through the device. If that is the case, the TPS79933 or TLV70033 should provide a similar result as the MAX8891 part.


    Regards,

    David

  • 0 in reply to David Hopkins
    Prodigy 10 points

    Hello,

    Sorry no screen capture yet.  Noise on output is ~250mv sine wave at 10kHz.  Ripple on input is similar in shape but at~5mv.  Power is from battery.

    Thanks,

    Joe

  • 0 in reply to Joe Ziehler
    TI__Expert 8905 points

    Hi Joe,

    What else in your system is operating at 10kHz, such as I2C?

    Based on the PSRR curves for this LDO, PSRR is only a few dB at 10kHz so anything near that may cause these problems (basically, picture this as being a high-impedance supply at 10kHz...source current at 10kHz, and you will see large voltage drop).

    This would be rectified by using one of the other two LDOs mentioned above, or you could use some really massive bulk capacitors. I would suggest the TLV70033, which is P2P with the TPS78233 is the TSOT package.

    Regards,

    David