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LMX2571: How to use POWERDOWN and Multiplier

Part Number: LMX2571

Dear Specialists,

My customer is considering LMX2571 and has questions.

I would be grateful if you could advise.

---

(1) When F1F2_MODE=1 and POWERDOWN are used in combination, are there any limitation.

(2) Currently, by toggling TrCtrl 100 μs after return from "POWERDOWN" state,

I believe that PLL locks reliably without resetting FACL_EN

Is it correct?

(3) According to the datasheet 6.5 Electrical Characteristics, Multiplier frequency range is described  

MULT input frequency  : 10 ~ 30  MHz
MULT output frequency : 60 ~ 130 MHz

If MULT_F1, MULT_F2 = 1 (Bypass), Is it necessary to keep this frequency range?

I am thinking to use OSCin>30MHz, Pre-divider=1, MULT=1 and Post divider=1, is there any problem.

(4) about MULT_WAIT setting

When MULT_F1=1 and MULT_F2=1, is it possible to set MULT_WAIT=0.

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I appreciate your great help in advance.

Best regards,

Shinichi

  • Hi Shinichi,

    (1) F1F2_MODE and Powerdown are two separate settings, they don't have any relationship.
    (2) Calibration is always required after coming out from powerdown state. If MULT=1, simply program R0 (with FCAL_EN=1) once to initiate calibration. If MULT > 1, power up the device by programming R0 with POWERDOWN=0 AND FCAL_EN=0, then program R0 again with FCAL_EN=1.
    (3) Right, if MULT=1, you don't need to follow the MULT input/output frequency range constrain. OSCin > 30MHz is fine. A higher OSCin frequency is recommended if MULT is not used.
    (4) If MULT=1, MULT_WAIT is ignored, you can put any value on it.
  • Hi Noel,

    Thank you for your reply.

    I'll share your suggestion with the customer.

    I appreciate your grea help.

    Best regards,

    Shinichi

  • Hi Noel,

    I sent your suggestion to the customer and I got an additional question.

    Could you please advise?

    ---

    1. After setting it as F1F2_MODE=1, F1F2_INIT=0, FCAL_EN= 1, and
    F1F2_CTRL=1,
      PLL is in a Lock state in F1. Next, CE-pin is set as Low and made to
    Powerdown.
    2. After 10 ms passes, CE-pin is set as High and it is made to return from
    Powerdown.
    3. But PLL is not locked by F1.
    4. Then, TrCtrl-pin is reversed after 100us progress, and F2 is selected.
    [Question]
     Does F2 lock depending on such usage?

    ---

    I appreciate your great help and cooperation.

    Best regards,
    Shinichi
  • Hi Shinichi,

    After step 2, you should program R0 again, this is necessary to initiate VCO calibration.
  • Hi Noel,

    Thank you for your quick reply.

    I'll share your suggestion with the customer.

    I appreciate your great help and coopetation.

    Best regards,

    Shinichi

  • Hi Noel,

    I sent your suggestion to the customer, he has an additional question.

    I would be grateful if you could advise.

    ---

    [Reply of TI ]
    After step 2, you should program R0 again, this is necessary to initiate VCO
    calibration.

    [Question]
    If the procedure of "4" is followed even when not doing out the
    above-mentioned step,
    is the calibration of VCO newly started and locked not by F1 but by F2?

    ---

    I appreciate your great help and cooperation.

    Best regards,
    Shinichi
  • Hi Shinichi,

    In F1F2 mode (F1F2_MODE=1), the VCO will calibrate every time you switch between F1 and F2. Datasheet Section 8.1.4 has more details.
  • Hi Noel,

    Thank you for your reply.

    I'll share your answer with the customer.

    I appreciate your great help.

    Best regards,

    Shinichi