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LMX2820: Unlocked at low temperature

jiayi.li
Prodigy 10 points
Part Number: LMX2820

Hi,

     We find that when setting frequencies of 4160MHz，using instant calibration ,at -10℃，LMX2820 can not be locked.

     Could you tell me how to resolve this?Thanks so much.

  • 0
    TI__Mastermind 28882 points

    Hi Jiayi, 
    Are you using the LMX2820EVM or your own board? 
    Is this seen on one unit or various units? 
    Is this random, predictable, etc.? 

    Regards, 

    Vicente

  • 0 in reply to vicente flores prado
    Prodigy 10 points

    Hi Vicente,

    On my own board.

    Various units.

    Predictable.When it is power on and the temperature rises,the problem disappears.

    Regards,

    Jiayi

  • 0 in reply to jiayi.li
    TI__Guru** 106770 points

    Hi Jiay,

    Could you help verify, if you program LMX2820 to 4160MHz without any calibration assist and Instant Calibration, will it unlock at any temperature?

  • 0 in reply to Noel Fung
    Prodigy 10 points

    Hi Noel,

    We are verifying it.Have you ever been in this situation before?Unlocked at low temperature with instant calibration on.

    Regards,

    Jiayi

  • 0 in reply to jiayi.li
    Prodigy 10 points

    It won't unlock if programmed to 4160MHz without instant calibration.

  • 0 in reply to jiayi.li
    TI__Guru** 106770 points

    Hi Jiayi,

    Please try below InstCal sequence, let us know if this sequence cannot fix the problem, thanks.

    Initialization register setting
    1. Set DBLBUF_PLL_EN, DBLBUF_CHDIV_EN, DBLBUF_OUTBUF_EN, DBLBUF_OUTMUX_EN = 1
    2. Set DBLR_CAL_EN = 0; INSTCAL_SKIP_ACAL = 0
    3. If VCO doubler is required, set INSTCAL_DBLR_EN = 1, otherwise set this bit to 0
    4. Set INSTCAL_DLY = T x fosc (in MHz) / 2^CAL_CLK_DIV, where T = 2.5 x CBIASVCO / 0.47µF. CBIASVCO is the bypass capacitor at pin 3
    5. Configure other registers to lock to 5.65GHz without any calibration assist
    6. Set INSTCAL_PLL_NUM = 2^32 x (PLL_NUM / PLL_DEN)
    Programming
    7. Vcc power up LMX2820
    8. Program all the registers, LMX2820 should lock to 5.65GHz
    InstCal calibration
    9. Program INSTCAL_EN = 1
    9.5 run Index routine
    10. Program R0 (with FCAL = 1), calibration will begin
    11. Wait 100ms
    12. Program R0 (with FCAL = 0) to complete the calibration
    13. If LD pin did not turn HIGH, program RESET = 1 to reset LMX2820. After LMX2820 is reset, repeat Step 8 to 12
    Changing VCO frequency
    14. Program INSTCAL_PLL_NUM, PLL_N, PLL_NUM and PLL_DEN (if their value have change)
    15. Program R0 (with FCAL = 0) to change VCO frequency

    9.5 Index routine
    1. Program R106[10] = 1 (0X6A 0400)
    2. Program R107[5:0] = 0 (0x6B 0000)
    3. Program R108 = 0 (0x6C 0000)
    4. Program R109 = 0 (0x6D 0000)
    5. Program R106[9:0] = 514 (0x6A 0602)
    6. Program R106[11] = 1 (0x6A 0E02)
    7. Program R106[11] = 0 (0x6A 0602)
    8. Repeat step 5 to 7 for R106[9:0] = 515 to 519
    9. Program R106[10] = 0 (0x6A 0000)