RTL8211C & RTL8211CL
Datasheet
8.5. Efficiency Measurement
The efficiency of the switching regulator is designed to be above 75% in gigabit traffic mode. It is very
important to choose a suitable inductor before Gerber certification, as the Inductor ESR value will affect the
efficiency of the switching regulator. An inductor with a lower ESR value will result in a higher efficiency
switching regulator.
The efficiency of the switching regulator is easily measured using the following method.
Figure 16 shows two checkpoints, checkpoint A (CP_A) and checkpoint B (CP_B). The switching
regulator input current (Icpa) should be measured at CP_A, and the switching regulator output current (Icpb)
should be measured at CP_B.
To determine efficiency, apply the following formula:
Efficiency = Vcpb*Icpb / Vcpa*Icpa
Where Vcpb is 1.05V; Vcpa is 3.3V. The measurements should be performed in gigabit traffic mode.
For example: The inductor used in the evaluation board is a GOTREND GTSD32-4R7M:
• The ESR value @ 1MHz is approximately 0.712ohm
• The measured Icpa is 160mA at CP_A
• The measured Icpb is 400mA at CP_B
These values are measured in gigabit traffic mode, so the efficiency of the GOTREND GTSD32-4R7M can
be calculated as follows:
Efficiency = (1.05V*400mA) / (3.3V*160mA) = 0.80 = 80%.
We strongly recommend that when choosing an inductor for the switching regulator, the efficiency should
be measured, and that the inductor should yield an efficiency rating higher than 75%. If the efficiency does
not meet this requirement, there may be risk to the switching regulator reliability in the long run.
CP_A
CP_B
Figure 16. Switching Regulator Efficiency Measurement Checkpoint
Integrated 10/100/1000 Gigabit Ethernet Transceiver
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Track ID: JATR-1076-21 Rev. 1.3
ETC [ ETC ]
