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SYNC and SYSREF for ADC34J45

ttd
Mastermind 7660 points
Other Parts Discussed in Thread: ADC34J45, ADC16DX370, ADC34J45EVM

Dear Technical Support Team,

I have some questions about ADC34J45.

The datasheet describes just typical specification of VIH、VIL、V(CM_DIG) for SYNC and SYSREF.

It is difficult to make an interface schematic for ADC34J45 with these datasheet specs.

On the other hand, ADC16DX370 describes the details of DC spec and internal schematics.

And it says the recommendation of DC or AC coupling.

 

 1.)

Do you have the detail of DC spec and internal schematics of Pin Functions(SYNC and SYSRE)?

2.)

How should we deal with V(CM_DIG)?

Which dose it describe internal or external common-mode voltage range? 

3.)

SYSREF seems to be ac coupled(LVPECL AC) on ADC34J45EVM schematics( Page.4 on ADC34JXXEVM-SCH_C.pdf ).

Does  V(CM_DIG)  effect  for internal common voltage?

4.)

SYNC is converted from LVDS to LVPECL on ADC34J45EVM schematics( Page.4 on ADC34JXXEVM-SCH_C.pdf ).

How Input differential voltage(VID) can  SYNC pin accept ?

Can it accept VID for LVDS?

ADC34J45 datasheet doesn't show it.

Best Regards,

y.i

  • 0
    TI__Genius 12965 points

    Yi,

    We are doing some data sheet updates and these questions will be addressed in those updates.  For the time being I will try to answer your questions.

    1. We currently do not include a functional diagram of the SYNC and SYSREF inputs.  We will try to get that included in the next update. The typical values for these input pins are VCM of 0.9V with a differential swing of +/-400mV.  We have used LVDS signals and they work fine.  For the datasheet revision we will try to include the range of VCM and the range of differential swing.

    2. You can use an LVDS signal for the SYNC and SYSREF.  The inputs will work for a range of VCM values.  The 0.9V is a typical specification.

    3. SYSREF can be AC coupled if the SYSREF will be toggling.  If the signal is very low frequency, DC or pulse, then it should be DC coupled to ensure that the differential signal does not settle to 0 which could cause the SYSREF signal to trigger randomly.  The VCM can have a range of values, the 0.9V is a typical spec.

    4. LVDS signal is ok.  We will specify the VCM and differential swing range in the update.

    Ken.