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ADS1282 vs. ADS1282H Input Impedance

Sterling Jones
Prodigy 10 points
Other Parts Discussed in Thread: ADS1282

I am implementing the ADS1282 for a hydrophone input, and the datasheet (Sheet 12, Section 9.1) states that the H version of the ADS1282 has an "improved input stage" for use with high impedance sensors such as a hydrophone.  However, this is all that I can find and I don't see any further information.  In the electrical characteristics, the differential input impedance is listed as 1Gohm, but with a common mode input impedance of 100Mohm.  Is this different for the H version?  When connecting a hydrophone to the input, it is essentially going to look like a 200Mohm || 1Gohm, which means that the input impedance is about 167Mohm and creates a high pass filter with the input from the hydrophone, depending on the hydrophone's capacitance.

Can you provide any additional information about the H version, or clarify if my understanding of the common-mode input impedance is incorrect?

Thank you.

  • 0
    TI__Guru* 98045 points
    Sterling,


    The ADS1282H had some changes made to the input stage to address some overload conditions. With some hydrophones and charge-type sensors, source common-mode impedances can be high. As mentioned in the datasheet, when the terminating resistances are less than 50kOhms, use the ADS1282, when the terminating resistances are > 50kOhms use the ADS1282H.

    With higher terminating resistances, it was more difficult to recover from a transient overload condition in the front-end PGA in the original ADS1282.

    Looking into the inputs of the device, both should have a similar high input impedance. Note that the input impedance is just sampled charge and discharge of input capacitance as described on page 12 of the ADS1282 datasheet.


    Joseph Wu