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# LT1966 LT SPICE SIMULATION

hii my name is aied and i want to use the LTC1966 trms converter

so i built circuit   in lt spice and used an a capacitor of 0.1uf at the output in order to get the response time at the output .

and i feed the LTC with a sine wave with an a amplitude of 0.25v and frequency of 50 hz

sense TRMS converter is  suppose ti measure the heat value of the signal i expected to see on a 0.25VPP sine wave a dc output around 1 volt .

i calculated the area between the X axis and the  sine with the 0.25v amp graph from 0 to 2*pi and i got an answer of 1.

so i am suppose to see in output of 1 v    .(SENCE THE TRMS is the area between the graph and the x axis )

but i got a different result a ripple with about 200mv max and 100mv min

i expected to see a dc  voltage of 1v with much more smaller ripple

i attached picture from the lt spice and i wonder if i did something wrong ?

my goal is to measure a TRUE RMS signal with an amplitude ranges from 0 to 3.3volts and frequency of 50 to 60 hz max ,i would be very thankful for your help .

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• Hi aiedb:

In your circuit, IN1 is being driven negative while the LTC1966 does not have a negative supply.  In order to use LTC1966 on a single supply, use the circuit shown in the datasheet, Figure 9b.

Also, with a 250mVpk (500mVpp) sinusoid, the correct RMS/DC level to expect from the LTC1966 is 1/root2*250mV = 176.8mV.