aclineneutralpower supply
Even though AC has no polarity, almost all the power supply AC inputs or most AC powered device input terminals indicate line and neutral terminals as L and N just like in the following example:
Is there a fundamental reason to wire line to L and neutral to N but not the other way around? Could you give an example what might go wrong if one connects neural to L terminal and line to N terminal?
Also I think (correct me if I am wrong) one should not connect the Neutral from the line to the ground from a PC.
Right. Never connect neither the phase nor the neutral of the mains to any node of a PC. If you did that, touching any node (including the chassis) of the PC could kill you.
Fig 21 on page 54 of the datasheet is then plain wrong?
It is not wrong. It just assumes that all nodes around the CS5490 and the "Application Processor" (including the "triangular" ground) are electrically isolated from any end user. This means that, if you want to connect a PC to the CS5490, you MUST insert isolation between them. Easiest: insert isolation at digital links like RX and TX (isolating analog links is much more complex), using either optocouplers or magnetic isolators like these ones (I've used many of them, and they work very well. They allow you to work at higher frequencies than with usual optocouplers. Some of them even allow you to transfer power to the other side (the isolated one). Look for "isoPower" in that same page).
Can I do it without the need of adding another power supply?
You need a power supply for the CS5490, which cannot be the same as your PC's power supply.
And what does a pointing down triangle mean compared to the more usual ground symbol?
Conceptually, the same. All of them mean grounds (0 V reference points, for their "local" circuitries), but different ground symbols mean different grounds.
The specification for the power supply states that the current limiting is "Automatic current limit/foldback". Foldback current limited supplies can cause problems with non-linear loads, especially those that draw substantially constant current. This is because there can be two or more stable operating points, one with the supply in constant voltage mode and one or more with the supply in current limit mode. A brief current spike could 'knock' the supply from one mode to another.
But this is somewhat speculative since we don't know the design of the power supply nor the IV characteristics of your product. It would however be worth trying a constant current limit supply instead.
This is an example of what can happen
Best Answer
One reason is that typically the internal fuse is on the live wire. In the event of a catastrophic internal failure causing a short to the PSU output the circuit will be dead when the fuse blows. With reverse connection the fuse might not blow and even if it did the internal circuit would be live.
simulate this circuit – Schematic created using CircuitLab
Figure 1. Left: correct. Right: incorrect.