• State Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 2 answers
  • Subscribers 20 subscribers
  • Views 308 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

LMX2571: Calculations for Numerator and Denominator values

LMX2571: TICS PRO automatic calculator

Mochi
Genius 3885 points
Part Number: LMX2571
Other Parts Discussed in Thread: CDCE6214, LMX2572LP, LMK00105

Hello,

We are aiming to get clock outputs 74.25MHz and 74.25/1.001=74.1758241758242MHz

74.25MHz setting easier but the other is quite complicated.

 

TICS Pro result is attached image. It shows Fvco=4747.2527472528MHz

However hand calculation result has discrepancy between TICS Pro.

Fvco = Fpd×Prescaler×N Divider×(Fnum/Fden)

Fvco = 13.5×4×87×(15302295/16777215) = 4284.989011

 

Is there some limitation of accuracy caused by bit length on TICS Pro?

How can we get 74.1758241758242MHz output from 27MHz Fosc?

Is there automatic divider calculator?

 

Regards,

Mochizuki

  • 0
    TI__Guru* 85380 points

    Hi Mochizuki-san,

    The N-divider value = Nint+ Nfrac. in this case:

    Nint = 87

    Nfrac = 15302295 / 16777215

    So the N-divider value = 87.9120879

  • 0 in reply to Noel Fung
    Genius 3885 points

    Hi Noel,

    Thank you for your prompt reply, I got the point.

    Actually we are working on to replace IDT 2ch clock generator 5V9885, but no need the function of Split spectrum and EEPROM then two of LMX2571 are one of candidate.

    But it seems no automatic divider calculator on TICS Pro, it is quite heavy task to create all of divider setting for requested output frequencies.

    Do you have any suggestion of ease to use 2ch clock generator with jitter clearing function device?

    Regards,

    Mochizuki

  • 0 in reply to Mochi
    TI__Guru* 85380 points

    Hi Mochizuki-san,

    Do you need LVCMOS output?

  • 0 in reply to Noel Fung
    Genius 3885 points

    Hi Noel,

    3.3V CMOS is processor input port type, but we can add level shifter device for 1.8V CMOS clock output.

    Minimum output clock is 27MHz, Maximum is less than 150MHz and Automatic calculation tool is mandatory this time.

    Can we pick such a device from clock device selection tool?

    Regards,

    Mochizuki

  • 0 in reply to Mochi
    TI__Guru* 85380 points

    Hi Mochizuki-san,

    The best part is CDCE6214, it support 1.8V LVCMOS output and has a fractional PLL to support your clock frequencies. Unfortunately, TICS Pro of this device does not support automatic frequency calculation.

    The next best solution is LMX2572LP, it is a fractional-N synthesizer with two differential outputs. You may need a clock buffer such as LMK00105 to convert differential clock to 1.8V CMOS clock. In LMX2572LP TICS Pro, you can type the desired output frequency, the tool will calculate the VCO frequency and divider value for you.

  • 0 in reply to Noel Fung
    Genius 3885 points

    Noel, 

    Thank you very much for your recomendation.

    We are going to study those devices.

    Regards,

    Mochizuki