Question of RESISTIVE LOAD   AD8657

Please, please advise me.


I read Datasheet of AD8657.

"For example 1 kΩ of feedback resistor and assortment of 1 MΩ of load cause load resistance equivalent in 999 Ω as a result by an output.

It's impossible that A.D. 8657/A.D. 8659 moves such heavy load, so the performance falls greatly."
24 of a revision B|20 page

If such design was performed, does AD8657 break?

Give my best regard.

  • 0
    •  Analog Employees 
    on Oct 3, 2016 10:58 AM

    Hello, 

    That will depend on what voltage output you are expecting. The rail-to-rail performance of the op amp is dependent on load current. You can check Figures 21, 22, 24 and 25 for more information. However, taking Figure 24 below as an example,:

    You would see that as the load current increases, the headroom of the output from the supply also increases. For a 10mA load, you would only be getting to within 1V of the rail. So I would say that if your output voltage is low such that the effective load current is low, there would be no significant degradation in performance. However, once you get to higher load currents, you may be better off using a different amplifier since you would not be optimizing the rail to rail capability of the amplifier. The AD8657 is also a micropower amplifier, so using it to drive heavy loads is not an intended application for this amplifier. 

    To put it shortly, no, you would not break the amplifier by using it this way provided that you operate within the absolute maximum ratings of the amplifier, but you would expect some degradation in performance.

    I hope this helps.

    Thanks, 

    Kris

  • Thank you very muchi.
    I get "The AD8657 is also a micropower amplifier".
    That never breaks without a reason in the rating, but headroom changes.