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Original question:

ADS5263EVM

ADS5263EVM: ADS5263EVM

Alena Koroleva
Prodigy 20 points
Part Number: ADS5263EVM
Other Parts Discussed in Thread: THS770006, ADS5263

Hello,

I have a question about Vcm in ADS5263EVM. In datasheet for ADS5263 I see the recommended common-mode voltage = +1.5V (+-50mV), and for THS770006 this voltage needs to be from +2.25V to +2.75V. However, in datasheet for ADS5263EVM (on page 38) Vcm = +2.5V. And this +2.5V goes to the ADC pin.

 Am I correct, that it's permissible to apply more voltage to the ADC's Vcm pin, than +1.5V? Could you explain please, why does the Vcm voltage affect on the lower limit of the ADC frequency? 

Sincerely,
Alena

  • 0
    TI__Expert 6040 points

    Alena, 

    thanks for reviewing the sch so carefully!

    THS has a different VCM requirement compared to ADS. in the EVM design, there is a uninstalled 0ohm resistor between 2.5Vcm and 1.5Vcm.  So in the current configuration, ADC input network gets 1.5V VCM and THS output is biased at 2.5V. the THS outputs are AC coupled , thus 2.5Vcm won't pass to ADC input network. 

    we designed the board that way in order to support other pin pin compatible operational amps, whose VCM may accept 1.5V. 

    Thanks!

  • 0 in reply to Xiaochen (Sean)Xu
    Prodigy 20 points

    Hello Xiaochen,

    thank you so much for the reply! It solved our problem.