thanks for the response..
Worst case power dissipation is 2.7W.
This 2.7W is a continuous static power dissipation? I thought I heard
or read 'packet transmission' somewhere - this suggests pulsations
that occur on prompt - with possible interruption for other functions
that may not require 2.7W dissipation. Is the input a human interface?
What kind of power source is used - does it contribute to the internal
dissipation (what is it's efficiency)? How long is the power source
expected (or proven) to last under this average worst-case power
condition? This can often be a more practical indication of
consuption/dissipation. Not a lot actually goes into free space as RF.
there is an exposed ground plane
on this chipset.. But this is facing towards the plastic body and
there is no clearance left.. Also, i've provided thermal vias below
this module(nearer to the shielding which cover the ICs)..
What is the proposed surface area of the plastic housing?
What is the proposed plastic material type and thickness?
here, the antenna is internal PCB antenna.. I'll check once again if
this can be used..
Getting the internal hotspot temperature nearer to the casing skin
temperature involves reducing impedance between the hotspot and the
skin. This means getting as much of the hardware in direct contact
with the internal skin wall as is possible.
The contact will cause the external skin temperature to vary from the
average, producing hotspots if the contact area is small.
Without contact, The internal skin wall temperature will be determined
by that of the internal ambient air. This then determines the
temperature of the electronics, then the hot spot. The characteristic
gradients throughout the electronics in air can be determined outside
of the case, by inspection.
The unit may not be kept at 55, but because of other components and
modules o the PCB, the ambient inside the box may rise to 55
You need to be more specific about the external operating ambient, as
this will determine internal temperature rises above external ambient.
yes sir, as the external casing is made of plastic, i guess the heat
can not be dissipated to the external environment.
It won't be dissipated anywhere else, unless it's hand-held or mounted
into some other absorbtive media.
This surface temperature limit will indicate permissible power
dissipation limits of the package contents, as a preliminary check of
design viability.
The question is whether the surface temperature will exceed acceptable
limits. What standards are you subject to? This should list the
permissible limits. Your sales department may have other ideas,
written on paper somewhere.
Plastic is generally a poor thermal conductor, so higher
safety-limited temperatures are often permitted than in those
instances where hand-held casings are metal, as the hand can cool the
plastic surface fairly quickly, ie without injury.
...............................................................
