AD7739 AIN Protection

The AD7739 datasheet states that the device can operate with +/- 2.5 volt inputs.

The Absolute Maximum ratings for the AIN pins are listed as -0.3V to AVDD + 0.3V which would appear to contradict the input voltage range.

I wish to use the device with an external instrumentation amplifier operating with supplies of ca +/- 15V and a ouput voltage range of +/- 2V in normal operation.

How should I protect the input of the AD7739 from overvoltage ouput of the instrumentation amplifier.

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  • Dear Chris

    Thank you for your reply. When I printed out the data sheet and studied it more carefully, I realized that the analogue input specification of +/- 2.5 V was for a differential input.

    The signals I am dealing with are very low frequency with a sample rate the order of 1 second or more so the dynamic performance is not really an issue. The signals have a range of +/- 2V so using an Instrumentation amplifier with a gain of one, I end up with a signal of +/- 2V from whatever reference I choose. I can obviously divide signal by a factor of two and use an ADC with an input range of 0 - 2.5 V, but this is not attractive as I will require eight precision dividers.

    My conclusion is that I am better off using an ADC with a +/- 2.5 input such as the ADS1258 or with an input range of 0 - 5V with an offset reference.

    Please let me know if you have any better ideas.

    Yours sincerely

    Lyn Roberts

Reply
  • Dear Chris

    Thank you for your reply. When I printed out the data sheet and studied it more carefully, I realized that the analogue input specification of +/- 2.5 V was for a differential input.

    The signals I am dealing with are very low frequency with a sample rate the order of 1 second or more so the dynamic performance is not really an issue. The signals have a range of +/- 2V so using an Instrumentation amplifier with a gain of one, I end up with a signal of +/- 2V from whatever reference I choose. I can obviously divide signal by a factor of two and use an ADC with an input range of 0 - 2.5 V, but this is not attractive as I will require eight precision dividers.

    My conclusion is that I am better off using an ADC with a +/- 2.5 input such as the ADS1258 or with an input range of 0 - 5V with an offset reference.

    Please let me know if you have any better ideas.

    Yours sincerely

    Lyn Roberts

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