Texas Instruments THS4503EVM - Manual (Page 24)

4-2
Circuit pathways should be made as symmetrical as possible for both
feedback pathways to minimize second and other even-harmonic content.
The printed-circuit board used with PowerPAD packages must have features
included in the design to remove the heat from the package efficiently. As a
minimum, there must be an area of solder-tinned-copper underneath the
PowerPAD package. This area is called the thermal land. The thermal land
varies in size depending on the PowerPAD package being used, the PCB
construction and the amount of heat that needs to be removed. In addition, this
thermal land may or may not contain thermal vias depending on PCB
construction. The requirements for thermal lands and thermal vias are detailed
in http://www−s.ti.com/sc/techlit/slma002 and
http://www−s.ti.com/sc/techlit/slma004.
Finally, all inputs and outputs must be properly terminated, either in the layout
or in the load instrumentation. Unterminated lines, such as coaxial cable, can
appear to be a reactive load to the amplifier. By terminating a transmission line
with its characteristic impedance, the amplifier’s load then appears to be
purely resistive, and reflections are absorbed at each end of the line. Another
advantage of using an output termination resistor is that capacitive loads are
isolated from the amplifier output. This isolation helps minimize the reduction
in the amplifier’s phase-margin and improves the amplifier stability resulting
in reduced peaking and settling times.