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DP83867CS: Power supply modes and sequence

Part Number: DP83867CS


I am planning a new design with SGMII interface and considering using the DP83867CS. I have some doubts related to power supply.

1) First of all, the DP83867CS can work in two or three modes, as I can see the difference is to use or not to use the VDDA1P8 pin, so what are the functions related to that power supply pin? Do I need that 1.8 V analog power supply? What is needed for? I am not clear if I have to work in two or three power supply mode.

2) I do not understand the power sequence. As I can see in page 112, it says "When operating in three-supply mode, the 1.8-V VDDA1P8 supply must be stable within 25 ms of the 2.5-V
VDDA2P5 supply ramping up
". I am confused because it says "VDDA1P8 supply must be stable" and I assume that VDDA1P8 is ON (stable on 1.8 V), but I can see in the sequence diagram (see figure) that VDDA1P8 is OFF while VDDA2P5 is ramping up. If the sequence diagram is correct, I understand that I have first to switch on VDDA2P5 (keeping VDDA1P8 off) and switch VDDA1P8 on 25 ms after. Am I right?

Thanks in advance.