ADC34J24: CDCLVP1204 interface ADC34J24 SYNC

Raj Kapadia

Part Number: ADC34J24
Other Parts Discussed in Thread: CDCLVP1204, LMH3401, LMH5401

I am looking to drive the ADC34J24 with a CDCLVP1204 as I need to distribute the SYNC to multiple ADC's.

The CDCLVP1204 has LVPECL output but the ADC34J24 requires 0.9V common mode voltage. Not sure how to interface the two devices because the supply to the CDCLVP1204 is 3.3V and the ADC is 1.8V.

5 months ago

0 William Pfennigwerth 5 months ago

TI__Expert 8231 points

Raj,

The CDCLVP1204 output will work, we will just need to move the common mode to the .9V. To do this we can put AC-coupling caps to remove the DC bias on the output of the CDCLVP (.1uF) and then use a voltage divider circuit to bias the outputs to .9V common mode.

Let me know if you have any other questions,

Will

0 Raj Kapadia 5 months ago in reply to William Pfennigwerth

Prodigy 10 points

hi Will,

I forgot to mention that I need to DC couple.

Raj

0 William Pfennigwerth 5 months ago in reply to Raj Kapadia

TI__Expert 8231 points

Raj,

Then the CDCLVP will not be the correct part as the LVPECL bias voltage is 2V. I will look into if we have a suitable replacement tomorrow.

Regards,

Will

0 William Pfennigwerth 5 months ago in reply to William Pfennigwerth

TI__Expert 8231 points

Raj,

Based on the ADC34J24 datasheet, the clock input must be AC-coupled.

Here is the appropriate termination for the CDCLVP1204 into the ADC.

Regards,

Will

0 Raj Kapadia 5 months ago in reply to William Pfennigwerth

Prodigy 10 points

hi Will, I need to distribute the SYNC input and not the CLK input. The CLK input is already AC coupled. The SYNC needs to be DC coupled.

Regards, Raj

0 William Pfennigwerth 5 months ago in reply to Raj Kapadia

TI__Expert 8231 points

Raj,

Sorry for the misunderstanding. I am going to loop in the ADC team to offer a suggestion. I was unable to find the schematic files for the ADC34J24 on ti.com but the ADC team should be able to assist you in understanding what output format your SYNC pulse should be and what the resistor network should look like to interface into their SYNC inputs.

Regards,

Will

0 Rob Reeder 5 months ago in reply to William Pfennigwerth

TI__Mastermind 25930 points

Hi Raj,

I would use the LMH5401 or LMH3401 as a level shifter to DC couple from the output of the LMK or CDC device to the ADC sync input pins.

This is how most customers do this interface.

Thanks,

Rob

0 Raj Kapadia 5 months ago in reply to Rob Reeder

Prodigy 10 points

hi Rob, I ended up using a biased three resistor voltage divider to set the proper terminating voltage and common mode voltage to the ADC34J24.

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ADC34J24: CDCLVP1204 interface ADC34J24 SYNC