FAQ: AD8362 RMS Detector: Equations for RMS Averaging Capacitor and Corner Frequency of Offset Control Loop

Document created by Larry Employee on Oct 28, 2009Last modified by enash on Oct 4, 2012
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Q.

What is the correct equation for the determining the corner frequencies associated with the rms averaging and the offset control loop in the AD8362 RMS Detector?

 

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A.

There are some errors in the Rev. D  datasheet. Under the heading “TIME-DOMAIN RESPONSE OF THE CLOSED LOOP” there is an equation

fLP = 1/(CLPF x 1.1 KΩ)


 

This is incorrect. The correct equation is:

FLP = 1/(CLPF x 1.1 KΩ x 2π)


 

In the section  “CHOOSING A VALUE FOR CLPF”, the equation is written as:

 

CLPF = 900 μF/(2π x FLP). 

 

This expresses the correct equation in a slightly different format

 

Equation 13 on page 21 of the Rev. D datasheet is also incorrect. The correct equation for determining CHPF, which sets the high-pass corner of the offset control loop is:


CHPF = 200uF/Fhp 

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