LMX2820: SYSREF clock not able to generate.

Akhila Challagundla

Part Number: LMX2820

Tool/software:

want to generate JESD clock and SYSREF from LMX2820, We were able to configure and generate RFOUTA_P/N as 6GHz. But we are not able to generate SYSREF CLK at SROUT_P/N. Attached the snap of my design, Please check and confirm we are missing anything?

over 1 year ago

0 Noel Fung over 1 year ago

TI__Guru** 113260 points

Hi Akhila,

What is your input, output and sysref frequency?

0 Akhila Challagundla over 1 year ago in reply to Noel Fung

Prodigy 40 points

Hi Noel,

Input Frequency (OSCIN) = 25MHz

Output Frequency ( RFOUTA) = 6GHz

SYSREF Frequency (SROUT) = 5MHz

0 vicente flores prado over 1 year ago in reply to Akhila Challagundla

TI__Mastermind 30692 points

Hi Akhila,
SYSREFREQ pin must see a low to high transition i.e. pulled high.

I see in the schematic the pins aren't connected.

Regards,

Vicente

0 Akhila Challagundla over 1 year ago in reply to vicente flores prado

Prodigy 40 points

Hi Vicente,

I have tried driving the SRREQ_P from 0 -->1 setting SYSREF_INP_FMT to CMOS mode. SRREQ_N is floating. Still there is no sysref clk .

Thanks,

Akhila Ch

0 vicente flores prado over 1 year ago in reply to Akhila Challagundla

TI__Mastermind 30692 points

Hi Akhila,
Please note SYSREFREQ pins need to be pulled HIGH and kept high - not just toggled.

Please try the following configuration while having SYSREF pins pulled high - I have confirmed this configuration works on bench.

Regards,

Vicente

SYSREF 5MHz out.tcs

0 Akhila Challagundla over 1 year ago in reply to vicente flores prado

Prodigy 40 points

Hi Vicente,

Thanks for sharing the setup file. I am able to generate SYSREF clock now. Is there any other way to drive SYSREFREQ pin high internally? Since I left it floating in my design.

Thanks,

Akhila Ch

0 Noel Fung over 1 year ago in reply to Akhila Challagundla

TI__Guru** 113260 points

Hi Akhila,

unfortunately there is no register setting to make this happen, we need to physically pull the pin HIGH to enable sysref output.

Clock & timing

Clock & timing forum

LMX2820: SYSREF clock not able to generate.