Hi everyone,

I'm looking at the schematics of the Arduino Micro and some things are not very clear to me.

1. How does the P-Channel MOSFET T1 work, assuming only USB is connected?
Here is what I think happens, please tell me if I'm correct - when USB is connected, Vusb is 5V, and the parasitic diode of T1 has some voltage drop, meaning there is now a potential on the source. Now, since Vin = 0V (NC/floating, is it the same as 0V?), Vgs is now negative and now the MOSFET is in saturation so that the +5V net now has 5V from the USB. Is this true?

2. What's the point of diode D2? And are C10 and C11 bypass capacitors?

Thank you!

 

I'm asking the second question because I am designing a circuit which connects to an Arduino Micro through the J5 and J6 connectors and I put a resistor - capacitor at the reset pin to automatically reset the Arduino with each power up of my circuit, and I wanted to know if it's necessary.

MOD: Clipped your images, easier to follow.

 

0v is not the same as n/c.

n/c means no connect, its not connected to 0v.

C11 and 10 are decoupling / noise suppresion

D2 ensures the reset voltage never goes above the power supply volts,

Arduino does not need a POR , the chip itself has one built in,

 

Thanks for your answer. Can you explain then how the circuit is powered if only USB is connected, or in other words how T1 works?

About the POR, are you sure? I've searched for this a couple of times but couldn't find any evidence it has one built in. I know the chip resets every time USB is connected (that's what the Arduino webpage says), so does this happen also when USB is not connected and voltage is supplied from a power source?