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ADS8318: Input over voltage

John Gray
Intellectual 310 points
Other Parts Discussed in Thread: ADS8318

What is the output behavior of the ADS8318 is over the range and over the +Va?  Specifically In+ and In- goes over or under the input range and exceeds the supply lines.

there are times our Op Amps will drive to 5.5V and -0.5V into the In+ and In- inputs through a 100 ohm resistor.  I know that input protection diodes will conduct and limit the voltages, but what does the output conversion do?  Does it go to Max or Min and stay?  Does it switch sign as it starts to go over voltage?  Does it sag from max as the input voltage goes over the max?  I didn't see anything in the datasheet that addresses this.

We are on a time constraint and welcome your help ASAP.

Thanks,

-John

  • 0
    TI__Expert 3675 points

    For differential Vin > Vref; output codes will be positive full scale. For differential Vin < -Vref; output codes will be negative full scale. Common mode of Vref/2 must be maintained at all times. If common mode is maintained, the converter will follow its transfer function. 

    As you pointed out, protection diodes will turn on and limit the input signal voltage between -0.3V and VA+0.3V. This will cause increase in the current drawn from driving op-amps. 

  • 0 in reply to RahulVK
    Intellectual 310 points
    Thank you RahulVK.