External 1.8V supply?

Question

Hello, just joined the forum to get some info on this. Can the W5100 use an external 1.8V supply? We have a design that needs to have the lowest power consumption as possible, and I’m wondering if we could save a little bit by using an external 1.8V supply. (It would be a buck (switching) regulator - more efficient than a linear type) Even saving about 100mW would be good. (Need to meet minimum standby power requirements… ) If it’s possible, then, what sort of timing requirements are there? Like, does the 1.8V have to come up after the 3.3V, does it have to come up with a specific dv/dt, etc… Looking forward to get some feedback! Thanks, -Ben

Coccoliso · Answer

From datasheet the “1V8_OUT” pin of W5100 is split and becomes 1V8D for the digital part and 1V8A for the analog part. The analog part is decoupled with a 1uH series coil and some capacitors. I can not answer on the timing of application of 1V8 but I saw that between version 2.0 and version 2.1 of the reference scheme is precisely the power and the decoupling between the analog and the digital part to have had the greatest differences therefore suspect that the designers have had problems in this regard.

Lelouch · Answer

[quote=“Coccoliso”]From datasheet the “1V8_OUT” pin of W5100 is split and becomes 1V8D for the digital part and 1V8A for the analog part. The analog part is decoupled with a 1uH series coil and some capacitors. I can not answer on the timing of application of 1V8 but I saw that between version 2.0 and version 2.1 of the reference scheme is precisely the power and the decoupling between the analog and the digital part to have had the greatest differences therefore suspect that the designers have had problems in this regard.[/quote] Yeah the inductor and capacitors are a filter, to filter out noise. (That’s what I think it is for, anyways) -Ben