Prahlad,

There is much more on the Analog Devices web site than just the data sheet of the AD637.

There is in fact a whole book. It doesn't seem to show up under a search of "RMS" or as a single URL. Let me describe how to find it. Go to the URL for the AD536A (another true RMS device),
http://www.analog.com/en/prod/0...%2C00.html
click on application notes, and take note of the different sections under the heading "Design Handbook". Probablt easier just to download the whole zip file. Happy reading!

The range of devices manufactured by AD is http://www.analog.com/en/subCat...5F,00.html

Some are cheaper than the AD637, and some are also second sourced by Maxim. As I recall the cheaper ones have a smaller input voltage range. If you can scale your input, you may be able to reduce the cost of the product.

The is another article here that you may find useful
http://www.analog.com/library/a...index.html
and as I implied earlier, a search for RMS will yield other application notes that may pertain to your specific needs.

Linear Tech also has some info at
http://www.linear.com/search/searchResults.do
In particular, I reccomend Design Note 288.

Aslo check out this Linear Brief from National Semi
http://www.national.com/an/LB/LB-25.pdf#page=1

I have used the AD536 and AD736, both as a stand-alone and interfaced to a processor, and yes they do have long settling times. There is a capacitor value that you can tweak that will trade off accuracy for settling time as I recall. Rather than use the processor approach, I opted for the external device to allow the processor time for other tasks, and to allow for different frequencies (up to 100Khz) and the crest factor (non-sinusoidal waveforms)

Regards
Aubrey