TVS (Transient Voltage Supressor) Diodes are a fast type of zener diode. The idea is that if an overvoltage occurs, they open and they sort that high voltage to GND (or another low voltage.
There are also (at least) two types of these diodes.
The datasheet you linked to, acts as a normal diode in one direction, and as a fast zener in the other, while the schematic symbol you used is for a TVS device that has two diodes in “anti-series”, which means means that they have a higher threshold (around 5V in your case) in either direction.
The other issue I was refering to is for the PWR_FLAG symbols. Search this forum or read the manual for more info. The way it works has been written down many times.
Edit:
If you want to use a diode as reverse polarity protection, then use a normal silicon, or an skottky diode.
TVS diodes are used for a different purpose. Often a DC current is barely specified in their datasheets.
I use these on external inputs for protection against surge and fast transients.
On your circuit the unidirectional type would be more suitable and should be VBUS to GND, bar end to VBUS.
Normally USB powered circuits don’t bother with this (see @retiredfeline reply) and have a low value resistor or inductor in series with VBUS
Ah okay. To be honest, I’m reusing parts from a damaged board and that’s the item it used and in that layout. I’ll be using a USB micro b port, so not particularly worried about polarity.
I’ll look at changing this then
Changed that bi-directional diode to a schotty and ironed out the errors. Just the one left on pin 33 but according to Arduino boards and others, that should be put to ground.
