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TMS570LC4357: TMS570LC4357 - GNSS/GPS L1 Band RF Interference

ofirbo
Prodigy 230 points

Part Number: TMS570LC4357
Other Parts Discussed in Thread: LAUNCHXL2-570LC43, HALCOGEN

Hello,

We have designed a custom PCB using the tms570lc4357 processor.

Unfortunately, we've discovered that when powered up, the PCB emits RF noise which is almost blocking entirely a nearby (about 30cm) GPS antenna (Here2) on the L1 Band (1575.42MHz).

We suspected that it had something to do with our design, but were surprised to find out that the development board LAUNCHXL2-570LC43 is causing similar results. It can be reproduced easily by using Android application like "GPS Test" next to powered-on Launchpad.

Is there any application note regarding this issue? RF shielding that can mitigate this?

Thanks,

Ofir

  • 0
    TI__Guru**** 200146 points

    Hello Ofir,

    Does your code outputs high frequency waveform on I/O pins (PWM, GIO, SPI, EMIF, etc)? What is the radiation level if no code is executed from the MCU?

  • 0 in reply to QJ Wang
    Prodigy 230 points

    QJ Wang said:

    Hello Ofir,

    Does your code outputs high frequency waveform on I/O pins (PWM, GIO, SPI, EMIF, etc)? What is the radiation level if no code is executed from the MCU?

    Hi QJ,

    The only high frequency waveform that we use is the Ethernet (100 MBit), and a PLL setting of 300 MHz.

    When the MCU is held at reset the radiation significantly drops (as viewed in satellite count and SNR on Android app), but we don't have professional RF equipment to verify that. 

    Thanks,

    Ofir

  • 0 in reply to ofirbo
    TI__Guru**** 200146 points

    Hello,

    The PLL clock traces is inside MCU. The MII clock (50MHz) or data might be the EMI source. You can check the RF strength without running ethernet code. The EMI is related to the PCB design.

  • 0 in reply to QJ Wang
    Prodigy 230 points

    Hi,

    Changing the PLL to from 300MHz to 200MHz really improved the GPS reception and reduced EMI. 

    Is there any optimal PLL setting to minimize EMI near GPS L1 band (1575.42MHz)?

    Thanks

  • 0 in reply to ofirbo
    TI__Mastermind 49120 points

    You can enable PLL output frequency modulation and see if that helps reduce the effect of the 300MHz clock domains on the fifth harmonic emissions. You can use HALCoGen to configure the modulation.