Measure opamp output Z

Sep 03, 2008 2 Replies

For anyone who's read my previous post you know that I'm using an MCP600x for an EA in an LDO. I first tried to do it in spice but the FET model and the EA aren't really designed for LDO's.I'm now doing it in MathCAD but I cant calculate DC gain as well as a pole location without knowing Ro.



The MCP600x datasheet doesn't have output Z versus frequency graph so I'm looking for a way to measure the output Z of the MCP600X.



I've found two ways to measure Ro.



This is from Apex



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They also suggest applying a sinusoidal signal to the input and measuring the rms current while sweeping the input frequency. Are there any other alternatives for measuring Zo or estimating Zo from the datasheet?



MCP600X Datasheet



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LDO Showing Cpar (effective input capacitance),and Rpar EA output Ro.



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DC gain of LDO.



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If you're still driving the gate of a mosfet, through a series resistor, inside a slow loop, the amp's Zout doesn't matter.

Spice should work fine here. Scribbling a Bode plot on a piece of paper should work too.

John

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