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LMX2572LPEVM: LMX2572LP EVM in a deterministic phase relationship between REF input & RF out

Bob Haagensen
Intellectual 370 points
Part Number: LMX2572LPEVM
Other Parts Discussed in Thread: LMX2572LP, TICSPRO-SW, USB2ANY, LMX2571

We want to use an LMX2572LP EVM board to demonstrate that we can set up a deterministic phase relationship between REF input and RF output. But it's not clear if the SYNC input on the EVM is set up to support this.

REF in = 49.92 MHz, RF out = 38.4 MHz.  This is a fixed frequency application.

From Fig 159 of the data sheet, I conclude this will be a Category 3 process. Fig 160 suggests that the SYNC pin should be driven with a differential signal but it's not clear from the EVM schematic if this circuitry is in place.

Can I configure the EVM board to provide a deterministic relationship, given these frequencies?

Thank you

Bob

  • 0
    TI__Genius 11900 points

    Hello Bob,

    I agree that this falls under category 3 sync.

    "The SYNC pin allows the user to synchronize the LMX2572LP such that the delay from the rising edge of the OSCin signal to the RF output signal is deterministic."

    The SYNC pin can accept a differential or single-ended CMOS input. Register R58 helps configure the SYNC pin accept LVDS or CMOS input. The default is configured to CMOS input. Please see "Table 65. Register R58 Field Descriptions".

    On the EVM SYNC is configured to accept a CMOS input. This signal can be provided via the USB2ANY and TICSPRO-SW.

    Thanks,

    Vibhu

  • 0 in reply to Vibhu Vanjari
    Intellectual 370 points

    Hi Vibhu,

    1. We're getting an LMX2572LP evaluation board, which comes with a Reference Pro interface board. We already have a USB2ANY module which is being used for an LMX2571 eval board. Is there any reason to use one i/f board over the other when working with the LMX2572LP board?

    2. Is it correct that the Sync signal can be generated in TICSPro and just routed through the USB i/f board? IOW, I don't need to worry about the SYNC SMA connector on the evaluation board?

    3. Table 136 and the following text on page 63 seems to suggest that extra circuitry is needed and that the sync signal should be in LVDS format. Does that only apply to the external SYNC SMA connector?

    Thank you

    Bob

  • 0 in reply to Bob Haagensen
    TI__Genius 11900 points

    Hello Bob,

    Bob Haagensen said:
    1. We're getting an LMX2572LP evaluation board, which comes with a Reference Pro interface board. We already have a USB2ANY module which is being used for an LMX2571 eval board. Is there any reason to use one i/f board over the other when working with the LMX2572LP board?

    No, there is not. The reference pro board has the USB2ANY integrated with an oscillator that can be used as a clock source.

    Bob Haagensen said:
    2. Is it correct that the Sync signal can be generated in TICSPro and just routed through the USB i/f board? IOW, I don't need to worry about the SYNC SMA connector on the evaluation board?

    Yes, this is how the EVM is configured. You can toggle the SYNC on TICSPRO-SW. It is in the "User Controls" tab in the "Pins" section. This may not be ideal for timing critical syncs required for Category 3.

    Bob Haagensen said:
    3. Table 136 and the following text on page 63 seems to suggest that extra circuitry is needed and that the sync signal should be in LVDS format. Does that only apply to the external SYNC SMA connector?

    These recommendations must be followed. The extra circuitry is for an LVDS SYNC input. The external SYNC SMA connector is configured for an LVCMOS input.

    Thanks,

    Vibhu

  • 0 in reply to Vibhu Vanjari
    Intellectual 370 points

    Hi Vibhu,

    Thank you for sorting this out. Just one more thing - you said   "This may not be ideal for timing critical syncs required for Category 3.". Am I likely to run into problems in using TICSPro to generate the SYNC signal? What would be the ideal solution?

    Thank you

    Bob

  • 0 in reply to Bob Haagensen
    TI__Genius 11900 points

    Hello Bob,

    Please refer to "SYNC Timing" section of the "Electrical Characteristics" table and "Figure 2. SYNC Timing Diagram". These conditions must be met for Category 3 SYNC.

    Since you do not have absolute control over this, it is kind of left to chance whether you meet the requirement. The OSCin frequency you are using has a period of ~20 ns.

    Thanks,

    Vibhu

  • 0 in reply to Vibhu Vanjari
    Intellectual 370 points

    Hi Vibhu,

    Ok, I'll give it a shot and let you know how it goes. Thank you for your patience and your help.

    regards,

    Bob