Problem with AD8293G80

I am trying out the AD8293G80 as a possible replacement for our current IA. The IA is used to amplify the output of a pressure sensor and pass the output to an A/D. I have hooked the AD8293 up as indicated in the data sheet but the output (either pin 4 or pin 6) reads 5.1 mV and doesn't change for any change in input. The input signal from the pressure sensor varies between 0 and 10 mV. The common mode voltage is about 2.44 V. The power supply voltage is 5V. I tried another AD8293 and got a similar constant output of 5.6 mV. The pressure sensor is working properly as is the A/D. Do you have any suggestions as to what might be wrong?

Thanks.

Parents
  • 0
    •  Analog Employees 
    on May 3, 2012 11:10 PM

    Hello ERussell,

    The minimum voltage you can set on the reference terminal is 0.8V above the negative supply. This would explain the behavior you are observing.

    I can think of two options for you:

    1. You can increase your reference level. However, since you have a 1.2V reference, this means you'll reduce your input range, and since this part has a fixed-gain, you'll need to increase your reference voltage as well to something like 2.048V or 2.5V. You could consider ADR430 or ADR431.

    2. If you can't change your reference voltage, you may want to consider a single-supply rail-to-rail instrumentation amplifier, such as AD8226 or AD8420. Even in this case, keep in mind that the output won't go all the way to zero, so you will need to provide some room for that. Also, for AD8226, you'll need to buffer the divider with an opamp before connecting it to the reference pin.

    Let me know if you have any additional questions.

    Regards,

    Gustavo

Reply
  • 0
    •  Analog Employees 
    on May 3, 2012 11:10 PM

    Hello ERussell,

    The minimum voltage you can set on the reference terminal is 0.8V above the negative supply. This would explain the behavior you are observing.

    I can think of two options for you:

    1. You can increase your reference level. However, since you have a 1.2V reference, this means you'll reduce your input range, and since this part has a fixed-gain, you'll need to increase your reference voltage as well to something like 2.048V or 2.5V. You could consider ADR430 or ADR431.

    2. If you can't change your reference voltage, you may want to consider a single-supply rail-to-rail instrumentation amplifier, such as AD8226 or AD8420. Even in this case, keep in mind that the output won't go all the way to zero, so you will need to provide some room for that. Also, for AD8226, you'll need to buffer the divider with an opamp before connecting it to the reference pin.

    Let me know if you have any additional questions.

    Regards,

    Gustavo

Children
No Data