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LMK05318BEVM: Using TCXO or OCXO on LMK05318BEVM

Zain Alishammat
Prodigy 220 points
Part Number: LMK05318BEVM
Other Parts Discussed in Thread: LMK05318B, LMK05028, LMK5B33216, LMK5B12212

Tool/software:

Hello

I would like to implement the 3-loop mode in the  LMK05318BEVM . For this i have to solder a TCXO since the TCXO or OCXO is responsible for frequency accurecy and stability.

Datasheet

On the EVM, however, the output of the soldered XO is routed together with the TCXO to the XO_P pin of the LMK05318B!, as described in the schematic of LMK05318B EVM User's Manual, page 9:

LMK05318B EVM user's guide

How to use the 3-loop mode in this case?

The second questoin relates to TICS Pro programm. Where can i bypass the input reference (PRIREF_P) to one the output (OUTx) in this programm using the REF Bypass Mux without setting registers manually, i mean with the Wizard tool?

BR

Zain

  • 0
    TI__Expert 3135 points

    Hi Zain,

    LMK05318B only supports 2-loop mode. LMK05028 can support 3-loop mode.

    For 2-loop mode on LMK05318B, you'd need to disconnect the onboard TCXO to connect the external TCXO/OCXO.

    Or you can use the onboard TCXO for XO_P and use the external TCXO/OCXO for PRIREF. This way, when DPLL locks to PRIREF, the device reference the frequency error of the external TCXO/OCXO.

    LMK05318B doesn't have an option to bypass the input to output. If this is for debug purpose, STATUSx pin can route input signal (divide by 2).

    We have an advance device LMK5B33216 that can bypass REF signal directly to OUTx. However, this is not a dedicate buffer device, so REFx on OUTx would have degraded performance.

    -Riley

  • 0 in reply to Riley Nguyen
    Prodigy 220 points

    Hi Riley,

    I read the wrong data sheet. How sillySlight smile

    I still have a question: can i use the DCO Mode in APLL-Only Mode?

    In the datasheet page 57 is mentiond "DCO mode can be enabled (DPLL_FDEV_EN = 1) when the DPLL is locked" means DPLL is being used.

    I can get around this problem by routing the output of APPL1 to one of the INx of DPLL exiting free-run mode or holdover mode and initiate lock acquisition.

    BR

    Zain

  • +1 in reply to Zain Alishammat
    TI__Expert 3135 points

    Hi Zain,

    DCO can only be used with DPLL.

    Routing APLL1 signal to INx for a DPLL lock will create a closed loop and will be unstable.

    If you want to use DCO mode, there are a few options:

    - Have APLL2 reference the XO to generate an output and route to INx. Then you might be able to use DCO to control APLL1 outputs. APLL2 outputs are not affected.

    - Or you can do a direct write to APLL num value. But output might be disrupted while programing and would need a reset to ensure operation.

    - LMK5B12212 is a similar device to LMK05318B, but with 12 outputs. It can support both APLL and DPLL DCO. It can also bypass XO and INx.

    Note that in DPLL mode, XO frequency must be in non-integer relation to BAW VCO1 2500 MHz.

    You can use XO frequency like 48 MHz, 19.2 MHz, etc., but 25 MHz can't be used with DPLL.

    -Riley