Try these references:

Burawoy, Michael. 1991. The Extended Case Method. In Ethnography Unbound: Power and Resistance in the Modern Metropolis, ed. Michael Burawoy et al., 271–287. Berkeley: University of California Press.

Burawoy, Michael. 1998. The Extended Case Method. Sociological Theory 16 (1): 4–33.

Gluckman, Max. 1961. Ethnographic Data in British Social Anthropology. Sociological Review 9 (1): 5–17.

Van Velsen, Jaap. 1967. The Extended-case Method and Situational Analysis. In The Craft of Social Anthropology, ed. A. L. Epstein, 129–149. London: Tavistock.

I have read them. But slightly confused on it. Kindly provide clarity

I'm not really sure what you find confusing.  Do you have a copy of Yin's book?  

Case Study Research. Design and Methods

(1994, Second edition. Thousand Oaks: Sage)

By Robert K. Yin 

If you need more after you take a look at Yin, I've done case study work but it has been a while so I may not be all that helpful.

Dear Mr Kittredge 

Thanks for your help.