Tool/software:
Both the LMX2820 datasheet as well as the register manual note that the formula to convert from register value to a temperature in °C is:
Temperature [°C] = 0.85 × rb_TEMP_SENSE – 415
I have conducted some measurements where I measure the case (top) temperature using a thermal camera while simultaneously reading the internal temperature register. With the thermal camera I measure a case temperature of 97 °C, whereas the internal sensor reports a temperature of 133 °C. The LMX2820 datasheet mentions a Junction-to-case (top) thermal resistance of 9.5 °C/W (all heat flow through top) and a Junction-to-top characterization parameter of 0.1 °C/W (no heat flow through top). Given an estimated power dissipation of about 2 W, I cannot explain the large (36 °C) gradient between junction and top.
The following post ~5 months ago on this forum seems to indicate that a different formula is to be used, and that the documentation will be updated: https://e2e.ti.com/support/clock-timing-group/clock-and-timing/f/clock-timing-forum/1320438/lmx2820-die-temperature-using-tempsense-readback
Can you confirm that the equation listed in the datasheet is indeed wrong and that the formula in the post linked above is correct?
