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LMX2572EVM: Can't change the default frequency

Eleni Daskopoulou
Prodigy 20 points
Part Number: LMX2572EVM

Hello,

I have been trying to configure the LMX2572EVM to output a 915MHz waveform. I was able to connect it to TICS Pro and load the default configuration. I have also been able to write to registers and verify that the value was stored properly (by reading back the values). When I change the N divider value though, I see no change in the output frequency.

Thank you

  • 0
    TI__Guru 73890 points

    Hi Eleni,

    After changing the N divider value (or any frequency related register that is within the PLL loop), we need to program R0 (click the CalibrateVCO button) once to calibrate the VCO.

    If you have enabled the double buffer function, you also need to click the CalibrateVCO button to make the N divider change effective.

  • 0 in reply to Noel Fung
    Prodigy 20 points

    Hello, thank you for your suggestion. I have already tried that with no success

  • 0 in reply to Eleni Daskopoulou
    TI__Guru 73890 points

    Hi Eleni,

    Could you provide the TICS Pro configuration at 915MHz output?

  • 0 in reply to Eleni Daskopoulou
    TI__Guru 73890 points

    Hi Eleni,

    My EVM does not have any problem with this configuration.

    If you can program the EVM to the default setting of 1500MHz, you should be able to make it lock to 915MHz.

    I have my board locked to the default of 1500MHz. Then I type 915 in RFoutA box, then change PFD_DLY_SEL to 2. After that, I click the CalibrateVCO button, the EVM lock to 915MHz output.

  • 0 in reply to Noel Fung
    Prodigy 20 points

    I tried this exact sequence, but I still can't get the output to change. Also, I don't know if this is relevant but the output is not locked at 1500 even though that should be the case based on the settings. The measured output is closer to 1.7GHz. Could that indicate an issue with the reference signal? Still, I am not sure why changing the N divider would not change the frequency at all.

  • 0 in reply to Eleni Daskopoulou
    TI__Guru 73890 points

    Hi Eleni,

    Let's find out why you cannot lock to the default of 1.5GHz first.

    Please check you have a 100MHz clock source at the OSCin pin. After Vcc power up and program all the registers, MUXout LED should be ON if the VCO is locked. If not, check the voltage at CPout pin and Vtune pin, their voltage should be same if there is no connection issue. 

    Make sure you've got green light in TICS Pro Connection Mode. You can verify your USB connection by programming POWERDOWN=1, a significant current drop shall happen.