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ISO224: Common-mode Output Voltage

Koshi Ninomiya
Expert 4105 points
Part Number: ISO224

Hi Team,

Tolerance of Common-mode output voltage of ISO224B is,
  VCMout: Min=0.48 x VDD2, Typ=VDD2/2, Max=0.52 x VDD2

Could you let me understand how the VCMout is generated?
Could you let me understand the reason why VCMout has +/-4% tolerance?

My customer is considering to use the ISO224B with Single-ended input ADC. ISO224 datasheet has "Figure 48. Connecting the ISO224 Output to a Single-Ended Input 5-V ADC", and they know it. But to reduce system cost, they are also considering to input to ADC directly from ISO224 output.
Thank you.

Best Regards,

Koshi Ninomiya

  • 0
    TI__Mastermind 47595 points

    Hi Ninomiya-san,

    I can't get into our device's inner working on the public forum, but as stated in the datasheet it is typically VDD2/2. The tolerance will be a result of process variation. 

    I cannot recommend sampling only one output from the ISO224 directly for the reason that you have pointed out, it will be less accurate and susceptible to noise in the system. The best thing to do is a differential to single ended conversion near the input pin of the ADC. This can be accomplished using a very low cost amplifier. If they do choose to only use one output, please terminate the other output to ground through a 10kohm resistor. 

    For more information, please see: