Other Parts Discussed in Thread: DP83TG720EVM-MC
Hi all,
we're evaluating the DP83TG720S-Q1 PHY with the DP83TG720EVM-MC evaluation module.
When reading the internal voltage & temperature sensors, we get realistic values for voltages, but implausible values for the temperatures.
We're calculating the temperature according the the formulas and values from the datasheet:
We captured temperature register values from -20C to 120C ambient temperature.
When we calculate Tj according to the formula and values from the datasheet (Tj1 / blue in the picture), we get implausible results.
It's unrealistic that:
- at Ta = -20 C, Tj is at -44 C: Tj can't be below ambient temperature
- at Ta = 120 C, Tj is at 166 C: with about 600 mW dissipation and RtJA=33 C/W, junction should be about 20 C above ambient, not 46 C
The calculated slope of the blue trendline is very close to 1.5, while the expected slope should be closer to 1.0 - since the power dissipation is almost static the junction temperature should rise at the same rate as the ambient temperature.
Is it possible that the slope_temperature_sensor = 1.5 from the datasheet is wrong, and that the correct value should be 1.0?
When we calculate Tj with slope_temperature_sensor = 1, we get much more realistic results. See Tj2 / orange in the picture above.
