I have used these types of components (QFN with Thermal Pad) at lot over the past couple of years. I add the PowerPad to the package symbol as four separate pins which form the one pad. The reason for this is because TI, among many other vendors, that use these packages recommends that four separate solder paste areas are used in the PowerPad area. To connect down to the GND planes I add vias inside the PowerPad area in the package symbol to immediately connect to planes once placed. I would strongly recommend you review the THERMAL INFORMATION section of the TI Spec sheet and also the TI QFN Application Report which gives you details on the solder pad and solder paste footprint requirements.
Attached to this post is an example of one of our QFN footprints which use a PowerPAD underneath the device. Underneath the device there is 5 vias shown as donuts because I have plated holes displayed, 4 top side smd pads which touch each other with stepped back solder paste apertures which space in between each.
Hope this help,
UTStarcom, Inc.Originally posted in cdnusers.org by mcatramb91