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Original question:

LMK05318: About LMK05318

LMK05318: About LMK05318 TCXO Selection

wenxing zheng
Intellectual 280 points
Part Number: LMK05318

Hello,

My LMK05318's  Two Reference Clock Inputs are 1pps and output5 is 1.8V CMOS 10Mhz, if two inputs lost and LMK05318 will be holdover mode, then the 10MHz output holdover stability  will depend on external TCXO.

My question is if in holdover mode,output clock needs meet Stratum 3/3E,then must  my TCXO use high accuracy TCXO,for example Stratum 3/3E TCXO or TCXO can use common device,for example +/- 0.5ppm TCXO?

Thanks.

  • 0
    TI__Mastermind 18070 points

    Hi Wenxing,

    A higher precision TCXO (0.5ppm) is recommended for 1pps input. Also, please make sure that this 1ppm is with reference to your PRIREF/SECREF otherwise the reference may not be validated.

    Regards,
    Hao

  • 0 in reply to Hao Z
    Intellectual 280 points

    Hello Hao,

    Thanks your comments.

    So my understanding is below:

    1. If PRIREF and SECREF are 1pps input, both  PRIREF and SECREF MUST has valid nput,don't support only one input,is it right?

    2.If the output clock needs meets,for example  Stratum 3/3E (my customer requirement is to keep in 1.5us over 48 hours in holdover mode) in holdover mode, the TCXO at least 0.5ppm ?

    I have a below try in lab:

    The TICS PRO 's default configuration has a mode: 1pps input,I export the Regs values and write these Regs values into my board LMK05318.

    I measure the output is 10MHz,but I can't make sure the 10MHz is from  PRIREF and SECREF's 1pps or from TCXO.

    I read reg R14=0xC0, that means Loss of phase lock DPLL=1; Loss of frequency lock DPLL=1.

    Does it mean the 10MHz is from TCXO?

    But I remove the 1pps inputs, then the Reg14=0xD0, means  Holdover event DPLL=1, I feel 10MHz locked the 1pps input based on Holdover event DPLL=1 .

    I don't know my understanding is ok or not, has any reg can judge  if 10MHz output locked  1pps inputs?

    Thanks.

  • 0 in reply to wenxing zheng
    TI__Mastermind 18070 points

    Hi Wenxing,

    No it's OK to have only one valid reference. You may find if easier to understand the device by looking into the GUI. Download the latest Ticspro and select LMK05318B

    For 1pps input, please use LMK05318B instead of LMK05318. The two are pin compatible. So if you already have an EVM then you can directly swap the part.

    The LMK05318B wizard in Ticspro will tell you that 10MHz TCXO cannot be used.

    And 12.8MHz TCXO is recommended for 1pps (or some other frequency that doesn't have an integer relationship with 2.5GHz. All the detailed explanation can be found in the wizard)

    Before checking DPLL_LOPL and DPLL_LOFL, the first step would be to set the reference validation (the new wizard does that automatically, and you can read through the instructions to understand what it's doing) and then check PRIREF_VALSTAT and SECREF_VALSTAT status registers. You need to first make sure that one of the 1pps references is valid. This requires high precision 1pps source (in the range of a few ppm, with respect to TCXO frequency)

    Once the reference is valid, the rest will be easy. 

    Regards,
    Hao

  • 0 in reply to Hao Z
    Intellectual 280 points

    Hello Hao,

    Thanks for you help!

    Maybe I don't describe my design clealy yesterday.

    Attached file is my design and is testing in custom field. So now it must use LMK05318,not LMK05318B.

    In Tiscspro GUI, I set TCXO=19.2MHz,output5=10MHz,then according to default config's 1pps export all regs values.

    Then write these regs values to my LMK05318. The result is output5 has  valid 10MHz output,but I read reg R14=0xC0,

    then I remove 1pps inputs, the Reg14=0xD0,that means Holdover event DPLL=1.

    Can I judge output5=10MHz locked 1pps input according to these observations ?

    Another question is about how to select TCXO.

    For example,my customer needs holdover 1.5us in 48 hours, what formulation can calculate the TCXO's accuracy,0.5ppm or higher-quality TXCO?

     

  • 0 in reply to Hao Z
    Intellectual 280 points

    Hello Hao,

    Can I export the regs values according to LMK05318B ,then write these regs values into my LMK05318?

    If the two device have same regs?

  • 0 in reply to wenxing zheng
    Intellectual 280 points

    Hello Hao,

    In Tiscspro GUI,when select  LMK05318B, the Set reference of Wizard hasn't PRI/SEC interface type selection.

    The exported regs values R46=0x11(AC-Diff), but I need COMS input type.

    Where can set the related regs in  LMK05318B wizard?

  • 0 in reply to wenxing zheng
    TI__Mastermind 18070 points

    Hi Wenxing,

    First of all, LMK05318B is recommended for 1pps because there's improvement made specifically for low frequency input, compared to LMK05318. In short, a DC buffer was added for PRIREF and SECREF to avoid being noise-sensitive at the input. Hysteresis level was also increased in case AC buffer is to be used 

    Second, reference interface can be set here:

    Third, you need to select backward compatible in the first wizard page if you insist on using LMK05318. However, there's a software bug for that mode - DPLL_LOFL won't clear. That bug has been fixed but the new version of Ticspro has yet been released. So for now, you can download the profile here: LMK05318B.zip

    In order to import this profile, go to Ticspro - Select Device - import user device - then choose this zip folder (don't unzip it). After that, go to Select Device again and choose User devices - LMK05318B.

    Finally, both DPLL_LOFL and DPLL_LOPL must be cleared to 0 before you can say that the DPLL is locked. The usage of status bits is explained in the last wizard page.

    Regards,
    Hao

  • 0 in reply to Hao Z
    Intellectual 280 points

    Hi Hao,

    In TICS PRO GUI  Step 3: set DPLL reference, if PRI/SEC=1Hz, no input type selection.

    My TICS PRO is V1.6.10.0.

  • 0 in reply to wenxing zheng
    TI__Mastermind 18070 points

    Hi Wenxing,

    That's because it's automatically configured as DC buffer. The Diff/SE and etc are only for the AC input buffer. Again, if you select "backward compatible" in the first wizard page then you'll see that AC buffer is always force selected because there's no DC buffer in the non-B version.

    Regards,
    Hao