I bought Iduino Due Pro from Geeetech recently. The board is considerably smaller than the original one, for the ATmega16U2 is moved on the external programmer board. Great.
HOWEVER, there is little (if any) documentation available, and schematics are missing. So, this if what I found out about my board:
- there are no operational amplifiers responsible for automatical power supply selection. The 5V pin of one USB, of the other USB, and output of the 5V regulator are connected DIRECTLY to each other. A little bit dangerous situation.
- I have only one board to test, but i found out that the 5V regulator (step-down converter, LM2734Y in the original DUE) has probably wrong discrete elements, and gives 7.8V instead od 5. It doesn't matter for the microcontroller, because this voltage is correctly converted in another regulator into 3.3V, which supplies the ARM.
But, the mentioned converter is meant to transform Vin voltage into 5V, which is connected to USB and to all 5V pins. What it means is, if you supply the board from external power source (i.e. 12V battery), and connect USB to program it - you can burn your USB port with 7.8V. My computer has built-in protection, luckily. And, you can burn your peripherials with the mentioned voltage.
However, I just put the 5V regulator out and replaced it with good old LM78L05, and it works perfectly with USB and battery connected.
So - this board has significant defects and be aware of them, but it's still usable and considerably smaller than original one.