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PSoC 3: opamp (follower mode) stability with 100 MFD load | Cypress Semiconductor

PSoC 3: opamp (follower mode) stability with 100 MFD load

Summary: 2 Replies, Latest post by Stub for 352898932 on 24 Dec 2013 02:59 PM PST
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lsen's picture
Cypress Employee
22 posts

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


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.

user_14586677's picture
7646 posts

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.

Stub for 352898932's picture
1 post

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 -


Regards, Dana.

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