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PSoC 5, 3 & 1

Anonymous
Not applicable

Will the opamp in PSoC 3 be stable in follower mode with upto 100 microfarad of load capacitance?

   

Ans:

   

With a 100MFD load, the opamp (in voltage follower mode) will be stable.

   

But it will have reduced bandwidth and hence, reduced slew rate. Phase margin is also very low leading to a longer settling time.

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ETRO_SSN583
Esteemed Contributor

It might be advisable to consider the effects a 100 mFD capacitor has

   

discharging thru output parasitic diode when Vdd falls to ground. Thats the

   

only discharge path C has and its thru a very small area (junction) diode.

   

And of course 100 mFD cap has a lot of charge in it, and potentially very

   

low ESR, read high currents result.

   

 

   

Regards, Dana.

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Anonymous
Not applicable

There is another issue with such high C load.

   

 

   

The OA stability may have been analyzed with output routed

   

directly to a pin. But if we employ routes thru muxes and other

   

components, out to a pin, then hang 100 mfd off pin, and take our

   

feedback from the pin, we have added a lot of phase shift due to

   

route R, and stability and phase margin will rapidly decline.

   

 

   

Useful reference - http://electronicdesign.com/power/what-s-all-capacitive-loading-stuff-anyhow

   

 

   

Regards, Dana.

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