LMK04828: Power supply filtering and Different pair outputs Reg.

Deva Guru

Part Number: LMK04828
Other Parts Discussed in Thread: TPS7A85, LMK04832

Hi ,

I have the below design query regarding LMK04828, I have a stringent requirement and i cannot have VCO/Any spurs coupled into my output.

1) Is High PSRR LDO required for VCC1-VCO supply or can i connect to common supply(derived using TPS7A85) that powers all VCC of LMK(Each pin isolated using ferrite bead)?

2) Can the VCXO also be powered from common supply(derived using TPS7A85) that powers all VCC of LMK or it needs to be fed using an separate LDO (isolated from LMK VCC power net)?

3) Can i connect DEV-CLK and SYSREF for DAC from different pairs and still synchronize ? eg: DEV-CLK from DCLKOUT4+ and SYSREF from SDCLKOUT7+

Thanks in-advance,

Deva

over 1 year ago

0 William Pfennigwerth over 1 year ago

TI__Expert 8421 points

Deva,

1) Having supply rails separated by ferrite beads as shown in the datasheet is our recommended filtering strategy. No separate LDO is required for datasheet rated performance. Although, adding a separate LDO for VCO supply could further reduce noise.

2) We recommend using a separate LDO for the VCXO.

3) Yes, you can.

Let me know if you have any further questions,

Will

0 Deva Guru over 1 year ago in reply to William Pfennigwerth

Prodigy 225 points

Hi,

Thanks for your reply,

Also one more thing,

Can i provide SYNC signal Deferentially DC coupled via clkin0 using FPGA LVDS standard(1.8V) ?

In datasheet DC coupled specification is mentioned only for MOS type with VIH >2V which is not possible if connected from FPGA 1.8V bank. Kindly advise.

Also, Does LMK04828 support R divider Reset for synchronization?

Thanks in-advance,

Deva

0 Andrea Vallenilla over 1 year ago in reply to Deva Guru

TI__Genius 10995 points

Deva,

Will is OoO and will get back to you by the end of the week.

Best,

Andrea

0 William Pfennigwerth over 1 year ago in reply to Andrea Vallenilla

TI__Expert 8421 points

Deva,

Thank you for your patience.

Yes, you can drive a SYNC signal to CLKin0 using dc coupled 1.8V LVDS. Make sure to set the CLKin1 Type to MOS.

LMK04828 does not support R divider synchronization. The LMK04832 supports R divider synchronization.

Regards,

Will

Clock & timing

Clock & timing forum

LMK04828: Power supply filtering and Different pair outputs Reg.