CDCM61004 with 50MHz LVPECL ouput

Ty Le Van

Other Parts Discussed in Thread: CDCM61004, CDCM6208, LMK03318, CDCE62005, CDCE62002

Hi,

This is the first time I'm using CDCM61004. I need 50MHz LVPECL output frequency. I would like to use 20MHz or 12MHz crystal as input

With Crystal is 25MHz, I see that CDCM61004 can not generate 50MHz

With Crystal is 12MHz, PR[1:0] = 10, OD[2:0] = 101, CDCM61004 ouput is 50 MHz

Could you please help me review above crystal frequency input, output divider, and feedback divider configuration?

Regards,

over 8 years ago

0 Alan O over 8 years ago

TI__Mastermind 32575 points

This configuration violates the crystal input frequency and phase detector frequency specs, so proper operation cannot be ensured and is not recommended.

If you can't use a different crystal frequency, can you consider another serially programmable clock gen device like CDCE62002, CDCE62005, CDCM6208, or LMK03318?

Alan

0 Ty Le Van over 8 years ago in reply to Alan O

Prodigy 80 points

Hi Alan,

Thank you so much for your support
What the value of crystal do you recommend for 50MHz LVECL output?

Ty

0 Alan O over 8 years ago in reply to Ty Le Van

TI__Mastermind 32575 points

26.66666 MHz input with feedback div=15, prescaler=5, and output div=8.

0 Ty Le Van over 8 years ago in reply to Alan O

Prodigy 80 points

Hi Alan,

I have finish schematic design for CDCM61004 with 50MHz clock output.

Could you help me review schematic?

Thanks & Regards,

TY LE

0 Alan O over 8 years ago in reply to Ty Le Van

TI__Mastermind 32575 points

Ok, but I don't see it attached?

0 Ty Le Van over 8 years ago in reply to Alan O

Prodigy 80 points

CLOCK_GEN_CDCM61004_280416.pdfHi Alan,

Please get attached file

Regards,

TY LE

0 Alan O over 8 years ago in reply to Ty Le Van

TI__Mastermind 32575 points

Your crystal is 26.65 MHZ, which is not precisely 26.66666(...) MHz. Since your input frequency is offset from nominal by about -625ppm, this offset will carry over to your output clock (49.96875 MHz ). Is this acceptable?

0 Alan O over 8 years ago in reply to Ty Le Van

TI__Mastermind 32575 points

Beside crystal frequency, what is the crystal load cap spec? If it is higher than 10 pF, you may need to add additional cap on the XIN pin to GND to match the load capacity spec (per section 9.3.3 in datasheet). Otherwise, the rest looks fine.

0 Ty Le Van over 8 years ago in reply to Alan O

Prodigy 80 points

Hi Alan,

I have searched in digikey but I can not find any crystal with 26.6666 MHz so I would like to use HCMOS Oscilator FXO-HC530-26.666 with 26.666 MHz . Is the part number is OK for my design?

Regards,

Ty Le

0 Alan O over 8 years ago in reply to Ty Le Van

TI__Mastermind 32575 points

What's your frequency tolerance spec for 50 MHZ clock?

Clock & timing

Clock & timing forum

CDCM61004 with 50MHz LVPECL ouput