What can cause a SP485 to burn

[El-Master]

In the attached circutry (its from a USB to RS485 converter), what could cause the driver SP485 to burn? I know a high voltage on the A and B wires could probably burn the SP485, but could for example a high load such as a terminal resistor placed between A and B also cause it to become overheated? Any other suggestions?

 

[keevvee]

Hi,

RS485 is a robust line and normally drivers designed for it are quite robust too. SP485 datasheet says it has an output current limit 250 mA, i.e. the load shouldn't burn it IMHO.

Question is why do you have the R3 and R4?

Were they mounted and are they really shorts? Shorting DI tot he RS485 line exposes it to all external events, transients, ESD, etc.

 

[El-Master]

Thanks for the information. I just found out that R3 and R4 is acctually not on the PCB Im using, so you can disregard these. So is it only a high voltage incorrectly placed on the A and B wires that can cause the SP485 to burn?

 

[keevvee]

I would be careful saying "only". It's the most likely cause, perhaps an ESD or a fast moving transient?
The datasheet doesn't state any high voltage protection. Give a look to LT1785, this one can handle much more
This however can't exclude for example a power supply error, that has baked your circuit ...