Hi,
We are using DP83630 chip in both Twisted Pair and Optical Fiber modes on an Omapl138-based board with Linux. In our hardware configuration, Vcc of the DP83630 is set to 3.3V and at power-up the chip always traps in Twisted Pair mode. For Optical Fiber mode, after power-up we write to the appropriate registers of the chip as follow:
- bit 6 is set to 1 in PCSR for enabling FX
- bit 9 is set to 1 in PHYCR2 for soft reset
We did some power consumption measurement at 100Mb/s. In Twister Pair scenario but with RJ45 cable not connected we are measuring 243mA and 3.15W for the whole consumption of my board (including the DP83630 chip). Similarly in Optical Fiber mode with optical cable not connected, we are measuring 262mA and 3.39W for the whole consumption of my board (including the DP83630 chip). The difference is then of 240mW!
To locate where this difference comes from, we did some temperature measurement. And we found that between the Optical Fiber and the Twister Pair scenarios, there is 4.3°C of difference at the DP83630 chip itself, and also 2°C of difference at the Omapl138. That is higher temperature in the Optical Fiber scenario. When we roughly convert these temperature differences we reach around 200 mW. That is almost equivalent to the difference of 240mW obtained while measuring the consumption of the whole board (including the DP83630 chip)
We are quite surprised by these results and would like to know if you have any hint on these. Particularly, does the DP83630 chip itself is supposed to consume much more power in Optical Fiber mode that in Twister Pair mode?
Thank you in advance for your help,
Regards,
Fabrice
