Re: 6cm rf?


Mark GM4ISM
 

Ben

160 C junction temperature  is pretty standard for this technology, the data that is missing is the thermal resistance, junction to case measured in C/W, and power added efficiency.  Without it you cannot calculate the permitted dissipation of the device and the expected output power WRT the junction temperature. Yes it can manage a P1dB of 2W  but maybe only with a 20% duty cycle for thermal considerations.

If the value  of thermal resistance is say 15C/W, then if you dissipate 5W in the junction, the junction rises to 75 degrees above the case,  that would be manageable as the heatsink would have to keep the case at a max of 85C

if the value is 30 then the same 5W dissipation would put the junction at 170C even if you kept the case anchored at 20C with a fantastic heat sink.

we can guess from the figures.. at 400mW the data sheets states that the max case temperature is 85C  and that this is at 5V and 600mA  That is 3W in, 400mW out   2.6W dissipation  ie about 14% efficiency

If you assume that  at these values the case temperature is allowed to approach the max of 85C the the junction will also be OK below 160 C, some 75C above case.  75/2.6 is  28.8 C/W thermal resistance.

Lets say the efficiency reaches 30% at the P1dB point of 2w out,  that would require a junction dissipation of 4.4W

With that thermal resistance which is a constant, the junction would be 127C above the case. Thus the case must not rise above 33C

Thats quite low, requiring a very good heatsink and likely a low duty cycle

These calculations make a few assumptions and may be quite a bit off, I may even have  made a slip on the calculator  but they look about right to me and support the supposition that  1W or maybe a bit more output, with good design and typical amateur duty cycles, is probably feasible.

There are a lot of devices out there that look good for really high output power at the P1dB point but being designed (thermally) for a lower mean power  means they just cant realise that P1dB for a useful time.  Not all data sheets tell you the whole story :(

Mark GM4ISM

On 20/05/2021 21:26, militaryoperator via groups.io wrote:
The data sheet from Skyworks does not give any thermal info and it may be that key down CW at 2W will overheat the junction.

160deg C Mark.


. if they work as advertised.  If they dont, send em back!
Mark GM4ISM


I doubt worth trying to send back to China. Still you get either a nice little project box or a nice heatsink depending on which you buy, hi. 

Ben,

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