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LMT01: RF susceptibility?

John Gerthoffer
Prodigy 35 points
Part Number: LMT01

Has anyone ever seen the temperature reading effected during an RF test?  

We see an effect on temperature that peaks at 350 MHz.   

A couple ideas we kicked around are;

  • Beat frequencies on the PWM?
  • Voltage rail variation on GPIO pin

Any suggestions or random thoughts would be welcome.

  • 0
    TI__Expert 5695 points
    The support team will contact you shortly.
  • 0 in reply to Jose Arteaga4
    TI__Genius 13650 points

    Hello John,

    there are no known issues regarding RF immunity with this device. 

    Which test standard are you testing to, and what output are you observing? Are you able to share the test results and setup parameters, as well as schematics and layout with our team to review? You can send me details in a private message if you wish. 

  • 0 in reply to Ben Kasemsadeh
    Prodigy 35 points

    EMC test was a stepped freq. sweep from 80 to 1000 MHz.  We were shooting it with approx. 320 MHz at 10V/meter for susceptibility testing.  Orientation (Horiz/Vert, front, back, side A, side B) didn't really matter.  The temperature reading was effected by a negative coefficient.  e.g.  Ambient temp was 84 DegF, as freq. swept from 200 to 320 MHz, the reported temperature dropped from 84 to -10 DegF respectively.  

    The readings from an ADS131 analog front end on our PCB were also effected in the 320 MHz +/- 25Mhz range.  This is mentioned because the AFE's temperature reading is used to scale the LMT01's temperature.  I don't know whether the issue resides with either of the TI parts, our power supply, both, etc.

     

    I'm checking on the schematic/layout review.

  • 0 in reply to John Gerthoffer
    TI__Genius 13650 points
    Hello John,
    the fact that both the ADS131 and LMT01 are affected is unusual. Can you change your test setup to apply a fixed voltage to the ADS131 input and repeat the sweep? If you are still seeing issues, then it would suggest that the issue is with the power supply.
  • 0 in reply to Ben Kasemsadeh
    Prodigy 35 points

    Cannot easily rerun test.  It was run at an EMC/EMI facility.

  • 0 in reply to John Gerthoffer
    TI__Genius 13650 points
    Hello John,
    I agree with you; it is not easy to re-run tests in an EMI lab. With two failing ICs in a similar frequency range on the same PCB, it is likely that failing immunity is a systems issue, for example caused by power management. Another visit to the EMI lab may help to rule out different parts of the circuit and isolate the problem.