LMX2594: Phase Matching between 2 LMX2594 devices

Deeksha M R

Part Number: LMX2594
Other Parts Discussed in Thread: LMK04828, ADC12DJ5200RF, , USB2ANY

Hi,

I'm using two LMX2594 devices with 2 ADC12DJ5200RF ADCs. The input reference for both LMX2594 is buffered input from OSCout of LMK04828.

RFoutB is used as SYSREF output. SYNC pin has CMOS input from one of the SDCLKout of LMK04828. (Differential to single ended buffer used).

With VCO_PHASE_SYNC_EN = 1, there's no JESD output. Making this 0 and setting MASH_SEED value to a desired number I'm able to shift the output and get phase matched output. But this is frequency specific. As the frequency changes, phase matching is lost.

I want to phase match between the two LMX2594 devices independent of frequency. How do I proceed?

over 4 years ago

0 Noel Fung over 4 years ago

TI__Guru** 108410 points

Hi Deeksha,

Which SYNC category and SYSREF mode you are working at?

0 Deeksha M R over 4 years ago in reply to Noel Fung

Prodigy 110 points

Hi,

I'm working with SYNC category 1(CHDIV = 2) and SYSREF(continuous) in repeater mode.

0 Noel Fung over 4 years ago in reply to Deeksha M R

TI__Guru** 108410 points

Hi Deeksha,

With Cat. 1 SYNC, you don't need a SYNC pulse to sync, set VCO_PHASE_SYNC = 1 should be good enough. Input and output should always sync.

to use SYSREF, did you make INPIN_IGNORE = 0?

To enable continuous SYSREF clock output at RFoutB, we should pull SysRefReq pin HIGH.

Can you share your TICS Pro configuration? We can review to see if anything is missing.

0 Deeksha M R over 4 years ago in reply to Noel Fung

Prodigy 110 points

Hi,

Sorry for the delay in reply.

Below are the screenshots of TICS Pro config of LMX2594.

When VCO_PHASE_SYNC is enabled, JESD link is not getting established.

With the below config, I'm able to get the JESD link up.

Also as I'm using SYSREF in repeater mode, SysRefReq is not always high. Is it necessary that for continuous SYSREF it has to be operated in master mode?

P.S. : INPIN_IGNORE is 0

0 Noel Fung over 4 years ago in reply to Deeksha M R

TI__Guru** 108410 points

Hi Deeksha,

I cannot understand why SYSREF did not work when VCO_PHASE_SYNC = 1.

Can you try the following debug? You should get continuous 62.5MHz clock from RFoutB.

2594sysref.tcs

0 Deeksha M R over 4 years ago in reply to Noel Fung

Prodigy 110 points

Hi,

There's no 62.5MHz clock output on RFoutB.

Since I'm operating in repeater mode, SysRefReq is not made always high; instead a SDCLK from LMK is connected to it.

0 Noel Fung over 4 years ago in reply to Deeksha M R

TI__Guru** 108410 points

Hi Deeksha,

The clock will be output only if you are in master continuous mode (SYSREF_REPEAT = 0) and there is a L-to-H transition at SysRefReq pin. To debug, could you disconnect SysRefReq from LMK and then connect it to USB2ANY so that you can provide a L-to-H SysRefReq transition?

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LMX2594: Phase Matching between 2 LMX2594 devices