Question: I have a chip, AMTEL AT32UC3A4256S, with multiple VDDIO pins on. Do they all need a 3.3V power input or just one?

The power schematic from AMTEL shows a single decoupled VDDIO pin in their schematic - enter image description here BUT the pin out has many VDDIO pins. enter image description here

Background: I am involved in a project as a systems engineer and another team is developing a custom PCB for an AMTEL AT32UC3A4256S. I decided that this would be a good chance to try and learn more about electronics and am doing some homework on the chip. It's a pretty complex chip to start out learning from but everything I find will be relevant to the project.

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    \$\begingroup\$ All VDDIO pins should be connected, even if they are shorted inside the package. \$\endgroup\$ – Mike Jan 21 '17 at 8:59
  • \$\begingroup\$ "Common for pin groups", and "Close to device (every pin)" it says in the image you posted. They've basically just grouped all the pins for simplicity in their diagram. \$\endgroup\$ – Tom Carpenter Jan 21 '17 at 9:06

Short answer is yes they should all be connected.

Two reasons spring immediately to mind.

  1. Current supply to the IO on the chip the IOs and power are connected by thin aluminum traces. If these do not blow immediately if trying to supply to much current there is a phenomena known as electro migration which will tend to make a thin point in the track thiner and lead to failure later. ie a reliability hazard.

  2. ESD protection circuits on the IO rely on the voltage at the IO pads being firmly controlled to prevent ESD damage and latchup. Each IO needs a voltage source reasonably close to it electricaly to achieve this.


Do they all need a 3.3V power input or just one?

the datasheet would have good answers on that. in general, they recommend you to connect all Vdd/GND pins. however, you can get by with connecting just some of them - not a recommended practice but i have used it from time to time, being lazy at those times.


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