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TPS782: Utilization for RF application

Juan Aparicio Jimenez
Intellectual 1890 points
Part Number: TPS782
Other Parts Discussed in Thread: TPS7A02,

Dear Power support team,

My customer is facing some problems with the utilization of the TPS782xx family for RF applications:

A significant noise generated of around 100 mVpp. 

Previously, they were using the TPS7A02 and didnt have any problem. 

Can you confirm that the TPS782xx are the same "good / efficient" than the TPS7A02 when used to power RF modems which can generate a lot of inrush current and which are extremely sensitive to noise?

I recommended:

- Checking the testing method: tip & barrel method

- DC bias of the capacitors

- Follow the Layout Guidelines

Do you have other recommendations? 

Thanks and best regards, 

Juan. 

  • 0
    TI__Mastermind 32600 points

    Hi Juan,

    I am reviewing your question and will reply within 2 business days.

    Thanks,

    Stephen

  • 0 in reply to Stephen Ziel
    TI__Mastermind 32600 points

    I Juan,

    We will need schematics and oscilloscope plots or test data showing this noise to diagnose the issue further.  We will also need to confirm they have taken clean test measurements using clean measurement techniques.

    Thanks,

    Stephen

  • 0 in reply to Stephen Ziel
    TI__Intellectual 1890 points

    Hi Stephen, 

    The decoupling capacitors used in our design with the TPS are the Samsung CL05A105KO5NNNC.

     

    From the graph in the DS, I can see that there is a 100mV ripple for a current burst of 10mA.

     

    The GNSS modem uses a strange power pattern with a lot of big current draws during acquisition.

     

    The GNSS modem forbids more than 50 mVpp of ripple amplitude on its power supply, which could be the issue here I think.

     

     

    Here is a plot of 2 of our designs:

    • in blue, M5_01 using TPS7A0218PDQNR
    • in yellow, M5_02 using TPS78230DRVR

     

    Decoupling capacitor are the same kind in both design, and the routing is 99.9% identical.

    As you can see, the yellow plot has much more noise it, resulting in a non-fonctionnal GNSS modem.

    Do you have some other recommendations?

    Thanks and best regards, 

    Juan. 

  • 0 in reply to Juan Aparicio Jimenez
    TI__Mastermind 32600 points

    Hi Juan,

    The TPS782 is a 13 year old design with less bandwidth.  As a result, its load transient performance is worse than the newer TPS7A02.  This means you will need more capacitance on the output to hold up Vout during these load transients.  Without knowing the details on the load transients (ramp rate, peak amplitude, dc current draw) I cannot give a recommended output capacitance.  But you can try increasing Cout to the maximum you can obtain in an 0402 package.  This looks to be 10uF rating, and after 3V bias you probably can achieve close to 4uF effective capacitance.  So an increase in 4x may be possible.  I would test that to see if the TPS782 performance improves.

    Thanks,

    Stephen