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ADC3660: Is the input full scale a 3.2Vpp?

Part Number: ADC3660


I'm checking ADC3660 datasheet.

This is its parameters.

 - input full scale : 3.2Vpp

 - input common mode voltage : 0.95V

 - VREF : 1.6V

With a differential driver IC, I have designed following.

 - Vocm for the driver : 0.95V

 - Vmin , Vmid, Vmax, Vfullscale of the driver output pins : 0.15V,  0.95V,  1.75V , 1.6V

With above parameters, I have a question.

In the ADC3660, the VREF is 1.6V and the Vmax of the input pin is 1.75V.

In ordinary ADCs,the Vmax of the pin is same to VREF.

So, I expected following new parameters.

- To use the VREF as 1.6V, change Vocm as 0.8V.

So, Vmin, Vmid, Vmax, Vfullscale of the dirver ic : 0V, 0.8V, 1.6V, 1.6V

And the Vfullscale of the ADC is 3.2V.

Q : Does the parameters of the ADC3660 correct?

     Do I must see it differently to ordinary ADC?     

     Or, does the my design for differential driver IC have mistake?

  • Hello,

    VREF should not exceed 1.6V under nominal conditions. Can you please share with me where 1.75V max for VREF is shown in the datasheet?

    Since the ADC3660's VCM is 0.95V +/- 0.05V, using a VOCM of 0.8V is not recommended.

    Please use the first differential driver configuration that you have shared: - Vmin , Vmid, Vmax, Vfullscale of the driver output pins : 0.15V,  0.95V,  1.75V , 1.6V.

    Best Regards,


  • Dear Dan,

    I edited again to understand easily.

    Followings are presents fixed and anothers.
    - Fixed conditions by the datasheet
    - Differential input full scale : 3.2V
    - max voltage of a input pin : Not presented.
    - VCM : 0.95V
    - VREF : 1.6V
    - Derived from fixed conditions
    - Vmid : 0.95V
    - Vmin : 0.95-(VREF/2) = 0.15V
    - Vmax : 0.95+(VREF/2) = 1.75V
    So, the input pin must permit the input voltage of 1.75V.

    Is it correct? Normally, in the fully differential ADC,
    the max voltage of a input pin is limited to VREF.
    Because, ADC can measure the input voltgae level with the VREF.

    I think I missed some important points. But the datasheet doesn't
    have any information about this.

    Best Regards,

  • Hi G.S Lee,

    Thank you for the clarification. Yes, I see why you are concerned. However, internally in the ADC, a shift in the VCM is performed, so the VREF is not actually violated. Similar to how the VCM on AINP and AINN are effectively cancelled during the differential subtraction inside the ADC. Please be reassured that the VREF will not be violated in the use case that we have discussed.

    Hope that helps.

    Best Regards,