The Thin shrinksmall outline package has a smallerbody and smaller lead pitch than the standardSmall [Outline Integrated Circuit|SOIC] package. It is also smaller and thinner than a TSOP with the same lead count. Body widths are 3.0 mm, 4.4 mm and 6.1 mm. The lead counts range from 8 to 80 pins. The lead pitches are 0.5 or 0.65 mm.
Exposed Pad
Some TSSOP packages have an exposed pad. This is a rectangular metal pad on the bottom side of the package. The exposed pad will be soldered on the PCB to transfer heat from the package to the PCB. In most applications, the exposed pad is connected to ground.
HTSSOP
The Heat sink thin shrink small outline package is Texas Instruments name for a TSSOP with an exposed pad on the bottom side. There are some other manufacturers who use the same name.