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I began working with Ethernet controllers and there is a recurring theme that keeps confusing me.

Currently I am incorporating the KSZ9031RNX into my design. The data sheet calls for digital and analog voltage supplies. My first thought is that I will need to incorporate a DAC in my PM circuitry.

However, when looking at the reference design for said chip, I notice that both supplies come from the same DC source, only to be separated by a FB. So does this mean the IC is taking care of the digital to analog conversion? I am just trying to understand this so I can move on.Thanks in advance.

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    \$\begingroup\$ i think that the datasheet is referring to separate power supplies for the analog and the digital sections ... it is not talking about a D/A converter .... the D & A means D and A \$\endgroup\$ – jsotola Aug 30 '19 at 17:01
  • \$\begingroup\$ Yes exactly. However, the reference design shows that both of these supplies come from a DC input. \$\endgroup\$ – circuit_noob533 Aug 30 '19 at 17:14
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DVDDH is the digital IO supply, which must match the other device's RGMII IO voltage. AVDDH is the tranceiver analog supply. They can come from same 3.3V supply if they both need to be 3.3V anyway. Decoupling one supply voltage into the digital and analog supplies with ferrite beads is good enough like in the reference design. There is no mention that these supplies should be separate.

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  • \$\begingroup\$ I don't understand why you are able to connect AVDDH to a DC voltage supply? Shouldn't it be connected to an analog voltage supply since it is analog? My confusion arises because the pin is labeled 3.3/2.5V analog Vcc \$\endgroup\$ – circuit_noob533 Aug 30 '19 at 21:53
  • \$\begingroup\$ @circuit_noob533 And you need to explain to us why you are confused, instead of just saying you don't understand why an analog supply pin is connected to DC voltage supply. What is your definition for an "analog voltage supply", and what do you expect to be connected to AVDDH pin instead? \$\endgroup\$ – Justme Aug 31 '19 at 7:28
  • \$\begingroup\$ Okay. I am confused because the analog supply pin is connected to a DC source. Shouldn't this pin be connected to an AC source since it is analog? I think the problem is that I am associating analog signals with ac power supplies. So when I see an analog pin connected to a DC supply I get confused. I am slowly beginning to realize how that can be problematic for me. Lastly, if I understand correctly, AVDDH & DVDDH are supply pins for the Digital and Analog parts of the IC? So they can be powered from the same DC source and not an AC source regardless of the type of signal? Apologies \$\endgroup\$ – circuit_noob533 Sep 3 '19 at 14:00
  • \$\begingroup\$ Chips in general do not take AC supplies - there might be exceptions though. It really is a DC supply for noise sensitive analog components inside the chip. For example an operational amplifier is an analog chip and it still needs DC supply. \$\endgroup\$ – Justme Sep 3 '19 at 14:52

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