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CC1120 RF power Problem

user4157937
Prodigy 120 points
Other Parts Discussed in Thread: CC1120

Hello

I'm trying to make a low power transceiver for datas with a CC1120 at 450 Mhz and a Microchip Pic microcontroller.

I use a developpement kit Smart RF TRXEB texas instrument (REV 1.7.0.3).

With the Pic microcontroller connected directly  to the CC1120_DK board wich is on the TRXEB board, all is OK, I can receive and transmit packets with a good power level.

After that, I made a personnal  board  following exactly the "450Mhz frerquency band " schematic by texas instruments, without the external osc option (I give you the link:   http://www.ti.com/lit/df/tidr227/tidr227.pdf  ).

On this board, there is a CC1120 embedded and a Pic microcontroller embedded (exactly the same program is running in the pic microcontroller), When I switch on the 3 Volts power, the SPI is working good because  I can obtain the IDLE mode or the TX mode. But When the TX mode is actived, the CC1120 try to run in TX during 5 seconds with a high current  50 mA or more (following the TX power programmed by the SPI), and I can see a little trace on the spectrum analyser, but His power is very small, and the frequency is not good, and the packets are not transmitted.  After 5 seconds, the high current stops (protection?...), and I must switch off then on the DC power to restart the system for 5 seconds.

I think there is an RF output  problem on the CC1120, but I don't know what is it... Can you help me please?

Best regards from France!

  • 0
    TI__Mastermind 39860 points

    If I understand correctly you tested your SW, which runs on a PIC, by connecting the MCU to a CC1120EM through the TrxEB. When testing with a good-known RF module (CC1120EM) you get the expected performance and the SW thus seems to be ok.

    When making your own design, with the CC1120 and the PIC on the same PCB, you do not get the expected performance and the CC1120 stops transmitting after 5 seconds. Agree that this sounds like a HW issue, and as a first step you need to measure on different CC1120 pins. Check voltage levels on pin 14 (RBIAS), the regulated supply pins (1.8V) and un-regulated supply pins. What about the crystal? Is this running continuously and at the right frequency? You write the "frequency is not good". Not sure what this means, but make sure that you calibrate the VCO when going into TX (use autocalibration when going from IDLE to TX) 

  • 0 in reply to Sverre
    Prodigy 120 points

    Hello Dear Sverre.

    Just before your answer, I found the reason of my problem, and I repaired it:

    On my board, I didn't sold all the metallic ground under the cc1120, The electric contact was good, but there was a thermal problem. The cc1120 tried to start , and stop after 5 seconds because it was too  hot. Now we solded the metalic ground, and all is OK,  like the datasheet.

    Thank you for your answer.

    Best regards from France.

    Benoît