Hi,
I'm reading temperature sensor LM73 every 100 ms. Can you explain me how to calculate the self-heating error along 24 hours of operation?
Thanks!
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Hi,
I'm reading temperature sensor LM73 every 100 ms. Can you explain me how to calculate the self-heating error along 24 hours of operation?
Thanks!
Hi Leonardo,
What is the power supply that you going to use for the LM73?
Aaron
Hi Leonardo,
There are several parameters to take into account in order to find the LM73 self-heating.
To determine the TJ of the LM73, you need to know the thermal resistance of the package (RqJA), the device power dissipation (Q) and the ambient temperature (TA). In the picture example attached, the heat flows from the junction (TJ) to outside ambient (TA), it shows the independent thermal resistances that make up RqJA. The thermal resistance of the PCB depends on how many layers that you are going to use.
1. Find Q, the maximum power dissipated by the device:
a. Let assume that you are using Vs(max) = 3.0V.
b. The maximum current in the datasheet is 320 uA.
c. To calculate the maximum power that the die is allowed to dissipate is Q = Vs(max) * Ips = 3.0*320 uA = 0.96 mW
2. Then Delta T, the temperature difference from the junction to the ambient
a. The LM73 thermal resistance assuming you have a 2-layer board and no airflow is RqJA = 186°C/W
b. Delta T = (Q)( RqJA) = (0.96mW)(186°C/W) = 0.179°C
c. The junction temperature can be calculated: TJ = delta T + TA = 0.179°C + 25°C = 25.179°C
Q is the power dissipated by the device.
TJ is the junction temperature in the device.
TC is the temperature at the case.
TA is the temperature at ambient.
TPCBis the temperature at PCB.
RqJA is the device’s absolute thermal resistance from junction to case.
RqJC is the device's absolute thermal resistance from junction to case
RqCPCB is the case absolute thermal resistance from case to PCB.
RqPCBA is the thermal resistance from PCB to ambient.
I hope this will answer your question. Please let me know if you have more question.
Aaron Heng