WIZnet Developer Forum

What is the recommended package size of pull up/down resistors?

I’m implementing a circuit referencing the W5500 ref with an integrated transformer. Since I have no experience of utilizing this, I would like to know how much the current in these resistors(49.9 & 10) would reach.

I checked some discusses and schematics from others to find that, 0402 and 0603 are used. But I’m worried that this is not big enough to satisfy power dissipation, especially for the 10 ohm resistor between 3.3V and TCT. If these pins go as low as 0V, current would be high.

I used 0603 for 49.9. As I work with W5100 there’s no 10 Ohm resistor, but for W5500 I guess it does not experience much current and serves as just a DC reference for the transformer’s central tap. But to be 100% safe wait for WIZnet engineer response.

I did some search and find that many PHY which have similar designs require 1/16W package for 49.9 and 10, if they are used. But 1/10W is used as well in some circumstances. It’s better for wiznet to provide detailed recommendation like other suppliers, especially when it’s more attractive for customers who are not very experienced with such design and demand highly integrated solution.

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