ADT7310
PCB design for optimized thermal performance
1. Overview
Temperature characteristic of the ADT7310 is dependant to
power dissipation and heat away of the PCB pattern.
Therefore, in design of the PCB pattern, Consideration of the
heat away characteristic is important.
ADT7310 package is designed to provide enhanced thermal
characteristics through the exposed PAD on the bottom surface
of the package. Exposed PAD effectively decrease the thermal
resistance, which in turn provides excellent heat dissipation
from the die.
In order to take full advantage of exposed PAD, the PCB must
have features to effectively conduct heat away from the
package. This can be achieved by incorporating thermal PAD
and thermal VIAs.
PCB to the bottom layers, thermal VIAs need to be
incorporated into the thermal pad design. The number of
thermal VIAs improve the package thermal performance.
Generally, web-constructed VIA is often used in through-hole
applications to facilitate the soldering of a pin to a large plane.
It has a large thermal resistance to the surrounding layer. For
this reason, do not use web-constructed VIA to the thermal
PAD. It is recommended use completely connected VIA to the
surrounding layer (Figure 2).
If the diameter of the VIAs is too large, solder will be pulled
away from the exposed paddle (solder wicking) during the
reflow process. This will decrease thermal characteristic of the
VIA
2. PCB Layout considerations
2.1 Heat transfer
For enhanced thermal performance, the exposed PAD on the
package needs to be soldered to thermal PAD on the PCB.
Furthermore, for proper heat conduction through the PCB,
thermal VIAs need to be incorporated in the PCB in the
thermal PAD region. The exposed PAD should be attached to
the ground plane for proper thermal and electrical
performance.
Figure 1 illustrates primary heat away through GND layer of
the PCB. The presence of large metal planes in the PCB can
heat away 90% of the generated heat in the ADT7310
(Reference 1)
<Figure 2. Thermal Landing and Thermal VIA>
3. Recommended PCB patterns
Figure 3 and 4 show adoptive PCB pattern of the ADT7310.
Top and bottom of the thermal PAD patterns are the same and
connected through the thermal VIAs. Also the bottom thermal
PAD must be connected to adjacent ground plane. It is recom-
mended that an array of thermal VIAs should be incorporated
at 1.0 to 1.2mm pitch with VIA diameter of 0.3 to 0.33mm.
<Figure 1. Heat transfer>
2.2 Thermal PAD
To maximize thermal performance, the size of the thermal
PAD should at least match the exposed PAD size. The size of
the thermal PAD on the bottom PCB layer should be at least as
large as the thermal PAD on the top PCB layer. It is
recommended that the bottom thermal PAD be thermally
connected to a GND layer (Reference 2)
2.3 Thermal VIAs
In order to effectively transfer heat from the top layer of the
<Figure 3. PCB land pattern – Top Layer>
* This specifications are subject to be changed without notice
Oct. 17. 2008 / Rev. 0.0
13/15
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