akh_power
Junior Member level 2
The datasheet of TI DP83822IRHBR and many other ICs recommend to use 49.9Ohm resistors as termination resistors for interfacing the PHY and RJ45. The screenshot of the circuit from the datasheet is attached. The resistor package usually recommended is 0402, which has a power rating 0.0625W. But, from the circuit it can be seen that if the differential voltage between RD- and RD+ is 3.3V (the IC power supply is assumed to be 3.3V), the power dissipated in each of the 49.9 Ohm resistor will be about 0.05445W. About 87% of the rated power. This does not satisfy the derating standard followed for many applications. Is there any mistake in the power calculation? How can be this be justified?