LMX2594: LMX-MultiDevice-Outputs-PhaseAlignment

Ajmal Rashid

Part Number: LMX2594
Other Parts Discussed in Thread: LMK04832

I'm using the #1Nos LMK04828B and #2Nos LMX2594RHAR in my design to provide #4Nos phase aligned sampling clocks from LMX to my device.

I referred some EVK and mapped the LMK to LMX as shown in the attachment. And i have some queries for the same,

1- If we are providing the phase aligned clocks from LMK (DCLK_OUT0 and DCLK_OUT4 with same length) to LMX-1 and LMX2, all LMX-1 and LMX-2 output clocks will be phase aligned?

2- What is the use of LMX-Sync pin? The Sync pin use is must for LMX output clocks phase alignment if we are using multiple LMX devices?

3- In my reference design, the both SDCLK_OUT are configured in LMK as LVDS and only connecting the 'P' of the output clock to the LMX-Sync pin through 0.1uF Capacitor. This is correct? or do you have any recommendation? ( FYI, both LMK and LMX are powered with 3.3V)

over 2 years ago

0 vicente flores prado over 2 years ago

TI__Mastermind 32152 points

Hi Ajmal,
1. If you provide a sync pulse to both LMX devices - yes outputs will be synced.

2. That is correct.

3. Refer to snippets below.

Regards,

Vicente

0 Noel Fung over 2 years ago in reply to vicente flores prado

TI__Guru** 119790 points

Hi Ajmal,

Your LMX configuration has the output frequency equals integer multiple of input frequency, you don't need the SYNC pin to sync. You only need to make VCO_PHASE_SYNC = 1.

0 Ajmal Rashid over 2 years ago in reply to Noel Fung

Prodigy 120 points

Hi Noel Fung,

Good to hear that.

For some application, I may generate fraction output also, so in this case sync pin is required rt?

Since i can only generate a differential signal from LMK SDCLOCK outputs, the terminations i provided from the LM SDCLOCK outputs to LMX-Sync inputs are correct?

0 Ajmal Rashid over 2 years ago in reply to vicente flores prado

Prodigy 120 points

Hi Vicente ,

Still i have not clear about the termination from LMK-SDCLOCK output to LMX-Sync input. From LMK-SDCLOCK output, i can only generate differential clock outputs (currently selected as LVDS), so the way i'm connecting from LMK-SDCLKOUT to LMX-sync pin is correct?

Do you have any reference circuit that shows LMK-SDCLK output to LMX-sync pin connections?

0 Noel Fung over 2 years ago in reply to Ajmal Rashid

TI__Guru** 119790 points

Hi Ajmal,

As Vicente pointed out, datasheet section 7.3.14.2.1 already explained how to deal with LVDS driver for sync pin.

Alternatively, you may consider to use LMK04832, it supports CMOS output.

0 Ajmal Rashid over 2 years ago in reply to Noel Fung

Prodigy 120 points

in the datasheet section 7.3.14.2.1, we can see one resistor is there between P and N , what is the value of the resistor to be used? The resistor to be placed near to LMX sync pin side Or differential clock source side?

0 vicente flores prado over 2 years ago in reply to Ajmal Rashid

TI__Mastermind 32152 points

Hi Ajmal,
Should be 100Ohms & on the Rx* side.

Regards,

Vicente

0 Ajmal Rashid over 2 years ago in reply to vicente flores prado

Prodigy 120 points

Hi Vicente,

In LMK datasheet, it is recommended to use the 100E and a coupling capacitor near to the receiver side for LVDS/HSDS clock output. So is there any problem if we are placing the 100E and near to the LMX sync pin side.

Thanks & Regards,

Ajmal Rashid

+1 vicente flores prado over 2 years ago in reply to Ajmal Rashid

TI__Mastermind 32152 points

Hi Ajmal,
Not a problem.

Regards,

Vicente

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LMX2594: LMX-MultiDevice-Outputs-PhaseAlignment