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Original question:

LMX2594: How to check pll lock.

LMX2594: VCO calibration speed:The actual test was 68uS.The manual says it can reach 35uS

user6062940
Intellectual 610 points
Part Number: LMX2594
Other Parts Discussed in Thread: LMX2572

Hi,

When we tested the frequency hopping time of LMX2594 and LMX2572 phase-locked loop chips, the VCO calibration used Partial assist mode, with the output frequency hopping between 1.0g and 1.1g. The frequency hopping time of LMX2594 was 68uS, which could reach 35uS according to the manual.LMX2572 test we found that the actual FM time difference is quite large compared to the manual.

What do we need to improve? Thanks!

  • 0
    TI__Guru* 81250 points

    Hi There,

    Could you provide your LMX2572 configuration? It will be great if you can provide it in TICS Pro format.

  • 0 in reply to Noel Fung
    Intellectual 610 points

    Dear，

    1875M.txt 
    R112	0x700000
R111	0x6F0000
R110	0x6E0000
R109	0x6D0000
R108	0x6C0000
R107	0x6B0000
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R91	0x5B0000
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R57	0x390020
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R48	0x300300
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R15	0x0F064F
R14	0x0E1E70
R13	0x0D4000
R12	0x0C5001
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R4	0x040A43
R3	0x030642
R2	0x020500
R1	0x010808
R0	0x00241C

  • 0 in reply to user6062940
    TI__Guru* 81250 points

    Hi There,

    The setting is for LMX2594 or LMX2572? I think you have issue with LMX2572 only, right?

  • 0 in reply to Noel Fung
    Intellectual 610 points

    Hi,

    The setting is  LMX2594.

  • 0 in reply to user6062940
    TI__Guru* 81250 points

    so you have problem with LMX2594 or LMX2572?

    I think you have issue with LMX2572, right? if this is the case, would you please provide the LMX2572 setting?

  • 0 in reply to Noel Fung
    Intellectual 610 points

    Hi ,

    We tested the LMX2594 Demo Board of TI,

    Frequency from 1.8G to 2.5G time is consistent with the manual.The time from 2.5g to 1.8g is longer than the manual.

  • 0 in reply to user6062940
    TI__Guru* 81250 points

    Hi There,

    OK, I think you want to shorten the VCO frequency switching time. Then, what is your target switching time?

  • 0 in reply to Noel Fung
    Intellectual 610 points

    Hi,

    Partial assist: 35uS

  • 0 in reply to user6062940
    TI__Guru* 81250 points

    Hi There,

    35µs is a very aggressive number, I am afraid it is not always possible with partial assist. You may consider to use full assist, which will bypass calibration and therefore save some switching time. However, you also need to ensure that your loop bandwidth is wide enough to support less than 35µs switching time.

    Please review the following appnote to get a sense of what kind of calibration assist can help you.

    www.ti.com/lit/snaa336