I searched in Rambam [hilchot Korban Pessach][1] and if I don't miss something, no Kappara (atonement) is mentioned. 

_Thanks to the answer of mevaqesh you can see [here][02] who is astonished by the Tosfot Yom Tov comparison between Pessach and taanit about  Kappara. The astonishing of Tif'eret Israel is perhaps also due to the lack of sources. 

But after an accurate lecture of Tosfot Yom Tov,  he also not said that the Pessach is Kappara. He said  a comparison between the sets: the  set of  korbanot and the set of  taaniot (not a comparison between the two items Pessach and taanit).  The major feature of the set of  korbanot is Kappara and  the set of taaniot also.  So Pessach as an item of the set of korbanot which is mainly characterized by  capara.  So the name capara is linked to pessach by his specie. 

But the [Levush Hachur OC 468, 1 ][03]  also  found by  @mevaqesh doesn't support this  teruts.  Anyway here It is possible to answer that to make himself exempt from caret because bitul mitsvat asse of Korban Pessach is Kappara but not at the sense of taanit. 



[1]:  http://www.mechon-mamre.org/i/9100.htm  
[02]: http://beta.hebrewbooks.org/pdfpager.aspx?req=40744&st=&pgnum=392&hilite=  
[03]: http://beta.hebrewbooks.org/pdfpager.aspx?req=9223&st=&pgnum=144&hilite=