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AD8546 'resistive load' limits

Thread Summary

The user questions the AD8546's ability to drive resistive loads under 100kΩ, despite its 11 mA short-circuit current and 15Ω output impedance specs. The final answer clarifies that the AD8546 is a micropower opamp, and its output swing degrades at higher currents, which is why it is rated for resistive loads down to 100kΩ. The output swing and load current figures (Figures 18 and 19) show that the opamp can maintain output within the headroom limits at 100kΩ loads, but performance degrades at lower resistances. The user's application, which requires unity-gain stability and a +5V supply, should still work with the AD8546.
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Recently I needed to specify a dual opamp with uncritical specs, for use in an oven controller:

(The other half of the amp interfaces the thermistor to the ADC, not shown.) 

A quick parametric search suggested that the AD8546 would be a good fit. Now that I'm looking closer at the data sheets prior to ordering, though, I'm seeing an unfamiliar warning:

What kind of opamp has problems driving resistive loads, and at the 100K level?!  Is this a misprint?  Nothing in the output impedance or short-circuit current specs suggests any limitations along these lines:

So I wonder if I'm missing something important here.  Any thoughts?  Obviously there are plenty of other opamps that will work in this application but before rejecting this one I'd like to learn more about the reasoning above.

Parents
  • Hi,

    AD8546 is a micropower opamp with 22uA maximum supply current at 18V designed and intended to be used for low power applications such as portable medical equipment and current loop drivers. Since it is low power, it is the reason it is rated to drive resistive loads down to 100kohms. Can I know what specs are important in your design?

     

     

     

     

     

     

     

Reply
  • Hi,

    AD8546 is a micropower opamp with 22uA maximum supply current at 18V designed and intended to be used for low power applications such as portable medical equipment and current loop drivers. Since it is low power, it is the reason it is rated to drive resistive loads down to 100kohms. Can I know what specs are important in your design?

     

     

     

     

     

     

     

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