TSOP(I) and TSOP(II) refer to thin profile small outline package with an overall thickness of as thin as 1.1mm (cf. 2.6~2.8mm for SOP of the same I/O). TSOP(I) and TSOP(II) differ in the location of leads. TSOP(I) lines its leads on the narrow side, while TSOP(II) lines up its leads on the wide side.