Thanks for all the responses.
Maybe use a P-MOS as a reverse protection? And looking into the datasheet this PIC has built-in clamping diodes to both rails, so a simple resistor my be enough for under- and overvoltage protection
The PIC will probably be ok but there are other components that need protection. I will have a look at some PMOS datasheets - trying to minimise parts but meet all specs.
Linear Technologies LTC4365 may be a good answer here. It protects from reverse polarity, overvoltage and undervoltage. I did a brief writeup here, with links to the data sheet and applications notes.
Thanks Jon, that nicely summarises the different protection methods. Whilst offering a nice solution the LTC4365 would be contributing the majority cost to the circuit so think it's a no go on this particular circuit.
If you replace the diode with a zener, it will protect from both overvoltage and reverse voltage. Replace the fuse with a polyswitch and it will recover after reverse voltage is removed.
What is the normal supply voltage range? What is the source impedance of the supply under abnormal conditions?
I haven't been given this information, the circuit has been designed to run at 5V and draws max 90mA.
Without the above info am I correct in thinking I can't choose PTCs / Zeners because I don't know how much current the supply can source and if more than the PTC Ihold max - poof!
And give us a totally inadequate specification of requirements (not that it stops people making up their own requirement and suggesting solutions to meet it).
"ESD Testing" is more or less meaningless.
Sorry that's my inexperience of not knowing what parameters are important and just trying to get an idea for what solutions are possible. The ESD testing is either IEC 810-2 or hand held discharge unit capable of 17kV, to be shocked 10x on each connector - Power, Gnd and two outputs - currently protected with the PESD5V0L2UU (if memory serves me correctly)
This is for the absolute most basic level of protection, that in my opinion should be deployed in every circuit made. If you expect to have LARGE voltages accidentally passed through the circuit you may want to consider something like a transient voltage supressor; if you need greater control over current protection you may wish to use both a fast acting fuse in the case of very high currents and a slow acting fuse for the small over currents; if isolation is key in this application you may wish to consider optical isolators et cetera.
The testing is just a requirement asked for - it shouldn't happen as the connector is keyed so unless they have an identical connector with reverse or higher voltage this shouldn't happen - it will be worst case there is a fault on the 5V rail. Fuses maybe an option but not at board level as the circuit will be potted making it a little more than tricky to replace