wiz820io not working at 3.3v working at 3.80v


Hi there,

I have a real mystery for you. I have a module I got recently, but it’s behaving strangely. It doesn’t work at all at 3.3v. SPI communication is working, but the linkStatus is always LinkOFF, and the network lights remain off. I thought it might be a power spike causing a brownout, so added a bypass capacitor, but that hasn’t helped either ( I’m powering it through a bench power supply, with a max current set to 1A. Out of desperation I switched the voltage up a little and it worked. 3.7v was enough. Any idea how this happened, is it just a faulty part? Do you know of any scenarios that can cause this to happen.

Thanks for your help.


Datasheet for W5200 says that maximal power voltage applied to the chip is 3.63 V, thus please refrain applying higher voltages.

Probably, but you must find what is wrong.

Means that digital voltage is ok for the chip.

Means that analog part experiences undervoltage.

If you look into circuit diagram for the module you see that there’re ferrite beads and capacitors involved with W5200_3V3A signal. The actual issue can be anywhere - from defective capacitor leaking current to the ground, to the ferrite bead soldered badly, and finally to the issues with the MagJack. Start with supplying 3.3 V to the module, and measuring voltage on the power lines - VDD_3V3D, W5200_3V3D, W5200_3V3A and W5200_1V8D.

Also ensure PWDN input is having steady logical low level allowing PHY functioning properly.


That’s really helpful, thanks for the response. I’ll give that a go, and report back results.