I’ve been having some problems with the 5V line on the Panda II.
In the past I’ve been using Domino’s boards. The 5V line differs not much from that value.
On the Panda II the voltage differs some tenths of a volt. I’ve tested two Panda II boards now, and the 5V line reads 4.64 and 4.62V. For the USBizi chip it’s not a problem, cause it will run at 3.3V.
I’ve been used to have a 5V display connected to the Domino. The minimum voltage needed for the display is 4.7, and now the display sometimes works and does not work.
I’ve also been reading about using the USB port on the Panda II as a USB Host on
There is noted to short diode D4 that normally protects the board to get the 5V at the connected USB device. The voltage on both Panda II boards at that point is about 0.4V lower than the 5V, that will cause some USB devices that were connected to mailfunction (e.g. USB to Serial converter).
To get the USB Host working, the 5V of IC3 was directly connected to the USB port pin. Now all USB devices connected did work.
Comparing the 5V circuit from the Domino and the Panda II, they both use a LM1117MP-5. On the Panda II there is an extra diode (D2) in series, that will cause the output of IC3 to drop about 0.4V.
I’ve looked the diode STPS140 up, it’s a power schottky rectifier, but that’s the point my analogue knowledge ends.
What is the purpose of the schottky rectifier D2, and why it’s not on the Domino board?
Can it be shortened to get a real 5V on the 5V line of the board, and what problems can shortening it bring?