• State
  • Locked Locked
  • Replies 4 replies
  • Subscribers 23 subscribers
  • Views 288 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LMX2595: Could not change the frequency

Doğancan Eser
Prodigy 10 points

Part Number: LMX2595

Hi Dear TI Team 

I development my own board with LMX2595. I can read and write registers as expected. I can measure the RF power from spectrum analyzer and change the rf power writing the register 44.  PLL is lock. The problem is that I can not change the frequency. I could not solve this problem . I am loading the register map that I extracted from TICsPro. and the code is below : 

LMX2595_writeReg(34, 0x0000);
LMX2595_writeReg(36, 0x0192);
LMX2595_writeReg(42, 0x0000);
LMX2595_writeReg(43, 0x0001);
LMX2595_writeReg(38, 0x0000);
LMX2595_writeReg(39, 0x0002);
LMX2595_triggerFCAL_only();

There is no problem about SPI and writing the registers. What can be the problem. 

void LMX2595_triggerFCAL_only()
{
    // 1) Read current R0 (e.g., your table ends with 0x241D)
    uint16_t r0 = LMX2595_readReg(0);


    // 2) Write back the SAME R0 but with only FCAL bit set
    //    (This triggers calibration; bit auto-clears internally after calibration)
    LMX2595_writeReg(0, (uint16_t)(r0 | LMX_R0_FCAL_BIT));
}

HexRegisterValues2.txt 

  • 0
    TI__Mastermind 19501 points

    Hi Doğancan,

    Can you provide what frequency you are initially outputting, what frequency you would like to change to, and what your Fosc frequency is?

    Thanks,

    Michael

  • 0
    TI__Guru** 121930 points

    Hi There,

    The configuration is fine except that we recommend set R25, DBLR_IBIAS_CTRL1 to 0x0C2B for better output power if you use the VCO doubler.

    Your configuration has R0 = 0x241D, which will power down the device, you should make it 0x241C.

    Your procedure to change frequency is correct, I don't see a reason why it does not lock to the new frequency. 

    Maybe the value of R36 is not correct. Is 192 decimal or hex?

  • 0 in reply to Noel Fung
    Prodigy 10 points

    Hi,

    I have solved  the issue. Registers values were not problematic. The problem was related to clock. Clock can not drive the LMX because of schematic mistake. However, PLL was showing the lock status as locked. Is there any possibility to understand whether correct frequency is in the output or not reading the some registers? This can be the good feedback for the operation ?


  • 0 in reply to Doğancan Eser
    TI__Mastermind 19501 points

    Hi Doğancan,

    The registers will provide clarity on the PLL_N and PLL_R values, as well as the other values that relate the Fpd, Fosc, and VCO values. Unfortunately, it will not provide clarity to the exact output value, as the value of the input/output frequency is not stored in the device. 

    The most appropriate way to measure the output frequency would be with a spectrum analyzer or oscilloscope.

    However, if the PLL is locked, then that implies that the VCO is phase locked to the input, implying that the input signal is valid. Can you probe the input to the device as well? Just to as a sanity check

    Thanks,

    Michael