Whether AD7792 chip can ON/OFF the Bias voltage very frequently

Hi,

My designing now use AD7792 chip to measure the thermocouple input.

AD7792 chip have the Bias voltage generator, it sets the common-mode voltage of a channel to AVDD/2. It is useful in thermocouple applications.

And, due to special reason, now, I need Open the bias voltage -> measure the thermocouple input(with BOOST bit active, This reducesBias voltage power-up time) -> Close the bias voltage, then, repeat this process forever. The time of each this loop process is 200mS about, it means that each 1 second, bias voltage need be ON/OFF 5 times.

Could you helps to check whether it is acceptiable for AD7792? whether it will damage the chip.

Thanks.

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  • 0
    •  Analog Employees 
    on Aug 2, 2019 7:27 AM

    Hi,

    May I know the reason why do you have to measure a thermocouple input without a bias voltage? The thermocouple voltage should be biased up so that the voltage on AIN+ or AIN- is within the acceptable range of the ADC. It set the sensor voltage DC operating point. When the common mode voltage exceed data datasheet limits, the ADC will still perform conversion, however, linearity and noise performance will degrade thus you may get an inaccurate or not reliable conversion. However, when the inputs exceeded the absolute maximum ratings it may cause permanent damage to the part. So it may not damage the part but we do not recommend to operate the part outside specification as we cannot guarantee its performance. That's why in most cases, biasing the input to the mid-supply ensures the thermocouple is within the input range of the ADC.  

    Thanks,

    Jellenie

Reply
  • 0
    •  Analog Employees 
    on Aug 2, 2019 7:27 AM

    Hi,

    May I know the reason why do you have to measure a thermocouple input without a bias voltage? The thermocouple voltage should be biased up so that the voltage on AIN+ or AIN- is within the acceptable range of the ADC. It set the sensor voltage DC operating point. When the common mode voltage exceed data datasheet limits, the ADC will still perform conversion, however, linearity and noise performance will degrade thus you may get an inaccurate or not reliable conversion. However, when the inputs exceeded the absolute maximum ratings it may cause permanent damage to the part. So it may not damage the part but we do not recommend to operate the part outside specification as we cannot guarantee its performance. That's why in most cases, biasing the input to the mid-supply ensures the thermocouple is within the input range of the ADC.  

    Thanks,

    Jellenie

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