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Derating Formula Confusion

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Ian.M:
I'd be somewhat inclined to interpret the  MLD-1640 datasheet as derate absolute power linearly, as that's what's the norm for nearly every other semiconductor device that uses linear derating.   If they want you to derate the dBm number linearly they should have explicitly said so.  However derating linearly by dBm would derate more aggressively at lower temperatures (still in the range 25 deg C to 100 deg C), so if in doubt, and in the absence of input from their application engineer, it would be more conservative to do that.

rstofer:

--- Quote from: Ian.M on September 12, 2019, 05:15:00 pm ---I'd be somewhat inclined to interpret the  MLD-1640 datasheet as derate absolute power linearly, as that's what's the norm for nearly every other semiconductor device that uses linear derating.   If they want you to derate the dBm number linearly they should have explicitly said so.  However derating linearly by dBm would derate more aggressively at lower temperatures (still in the range 25 deg C to 100 deg C), so if in doubt, and in the absence of input from their application engineer, it would be more conservative to do that.

--- End quote ---

It seems to me the datasheet said exactly that.  They gave a dBm value for 25 deg C and a dBm value for 100 deg C and told us to derate linearly between these endpoints.  It sure seems to me that they gave the endpoints of a straight line in terms of dBm.

Of course, I could be very wrong...

IanB:
I don't think dBm vs power makes much difference over such a small range. 20 dBm is 100 mW and 25 dBm is 316 mW. Half way between 100 and 316 is 208 mW, which is 23 dBm. So interpolating on the dBm scale to 22.5 dBm is conservative and therefore safe.

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