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Part Number: UCD9246
We would like to use the LM57-10 to measure the board temperature of our UCD9246 based design. This will be fed directly into the "TEMPERATURE" pin, w/o a mux.
Fusion Digital Power Design (FDPD) allows one to define a temperature sensor, and when I flip the "sensitivity" around in order to get sensor "gain" I end up with this selection window.
I guess it doesn't automatically calculate the voltage at 0C (2.202V)? Nor a sensitivity value? I just want to make sure I put this in correctly.
BTW, the LM57 has 4 different sensitivity curves, we're using J4 -> -10.339 mV/deg C, so it should be somewhat close to included LM94022.
Thanks, Best, Steve
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The committee that created the PMBus protocol choose to define several commands opposite of how they are typically defined by manufacturers.
Temperature is one of them.
Manufacturers will define sensor gain in mV/C while the TEMP_CAL_GAIN is entered as C/V.
So -10.39 mV/C will be 96.246 C/V.
And instead of specifying the voltage at 0C, PMBus uses the temperature at 0V.
In this case, you would take the voltage at 0C and divide by sensor gain.
LM57 isn't your typical analog sensor, the temperature to voltage curve, while appearing to be a straight line in the datasheet curves isn't specified as just Y=mX+b but is a polynomial which is specified over a relatively narrow temperature range (as least as far as I can tell with my brief review of the datasheet). I'm not sure if this would be the best selection for the UCD9246.
The polynomial "a" term is relatively small and could probably be ignored, with a loss in accuracy, then there is the "b' term which is multiplied by (Tambient - 30C). Although this could be accounted for by multiplying the -30C component with the gain and shifting it into a modified "c" term.
How this all plays out into the overall accuracy, I couldn't comment on. You might want to post to the forum which handles the temp sensor.
Is there a particular reason you chose this device, do you need the digital outputs?
In reply to Brad:
In reply to SteeVeeDee:
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