LMX2572LP: IDT 5V9885 replacement

Mochi

Part Number: LMX2572LP

Hello,

To replace IDT 5V9885 by LMX2572LP, we are running some case of simulations on TICS pro.

Target EE is video system, it is required 74.25MHz and 74.25/1.001=74.175824175824200MHz output to cover TV monitor filed clock and PC display filed clock from 27MHz reference input.

In the case of IDT 5V9885, divider setting is 27MHz x 160 / 58.24 = 74.175824175824200MHz

LMX2572LP case, closest frequency is 27MHz x 4 x (43+ 4106177524 / 4294967295) /64 =74.175824175906200MHz

This fractional type divider could not create punctual 1/1.001 ratio from 74.25MHz.

Would you give us idea to meet this requirement ? Should we change PLL device selection?

Regards,

Mochizuki

over 1 year ago

0 Julian Hagedorn over 1 year ago

TI__Mastermind 20900 points

Hi Mochizuki,

you need a fraction of 43 + 87/91 to get exact 74.25/1.001.

regards,

Julian

0 Mochi over 1 year ago in reply to Julian Hagedorn

Genius 3885 points

Hi Julian,

Thank you very much for your prompt reply during holiday season.

It is great support, TICS-PRO automatic calibration tool could not give us this number.

Is there any application note of fractional divider setting example to support major TV/PC video clock frequencies ?

Regards,

Mochziuki

0 Julian Hagedorn over 1 year ago in reply to Mochi

TI__Mastermind 20900 points

Hi Mochizuki,

unfortunately we don't have this application note.

I have done these steps:

1. Calculate VCO frequency: 74.25/1.001*64 = 4,747.2527472527472527472527....

2. divide VCO frequency with PFD update freq to get feedback divider in decimal: f_VCO/f_pfd = 43.956043956043956043956043....

3. entered this decimal in a decimal to fractions calculator: https://www.calculatorsoup.com/calculators/math/decimal-to-fraction-calculator.php

3.a. I entered 43.956043 and that I have 6 decimal places that are repeating.

That gave me the solution. Maybe you can do this with your needed output frequencies.

Note, you may need to change the output divider to achieve a valid VCO frequency.

regards,

Julian

0 Mochi over 1 year ago in reply to Julian Hagedorn

Genius 3885 points

Hi Julian,

I appreciate very much for your prompt assistance.

How useful this tool, we will continuously put the effort to replace IDT device.

Regards,

Mochizuki

Clock & timing

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LMX2572LP: IDT 5V9885 replacement