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ADC34J24: Questions about driving the ADC34J24 differential analog input

Part Number: ADC34J24

My customer is working to drive the differential input circuit on the ADC34J24, with a schematic similar to Figure 202 in the datasheet.  The Vcm output pin is at the 0.95V nominal level noted in the datasheet.  He would like to provide a relatively high drive amplitude of 2Vp-p differential, which is only specified in the datasheet as a nominal voltage for use with lower frequencies, which he complies with.  To further describe this scenario, I believe a 2Vp-p differential signal should correspond to peak voltage cases of 1.45V/0.45V and 0.45V/1.45V on the INP and INM rails, respectively, with Vcm = 0.95VDC.  Please correct me if I'm wrong!

The engineer would like some guidance with regard to this 2Vp-p signal level since it is a nominal spec.  We don't specify a max input voltage.  For proper operation (no clipping or distorting) do we recommend backing off the 2Vp-p by some amount?  He wants to make sure that this circuit will work well over PVT variations.  I'm assuming this guidance should also take into account some variation in the 0.95V Vcm level.

Thanks, David Hildebrand

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David Hildebrand
Analog Field Applications
Texas Instruments, Inc.
Office:  214-479-0917
Cell:       972-841-6499
david.hildebrand@ti.com
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  • Hi,

    You need to look at ADC's offset error spec and DC gain error spec. The datasheet specifies offset error as within +/-20mV. The gain error is specified as within +/-4%FS (including reference error). These specs mean for a corner lot device with extreme gain and offset error, you may reach positive saturation code of +1024 (signed binary) for a differential input of 0.94V( 0.96V -0.02V=0.94V). So, if your system has reasonable margin, it should be safe to keep analog input below -1dBFS which means 90% of Full-scale range (+/- 0.9V).

    Regards,

    Sourabh