I want to protect an IC output (MOSFET driver) that the vendor says can survive V_cc +0.3V on the output pin from an accidentially connected overvoltage of about 35V on the plug. Problem: my V_cc is only 5V!
One approach I found here at StackExchange EE was to use a combination of TVS and a PTC.
My assumption is, that the 35V will create a current trough the highside switch to V_cc of the MOSFET Driver or through the lowside switch to GND.
1) How will I know if the IC can survive the time that the PTC needs to become highly resistive? Can I look for hints in the IC datasheet?
2) I always thought TVS are meant for ESD or surge protection (short time and high voltages) and not for longer durations of moderate (35V) Voltages. Can they also be used for these things?
3) Whats a good starting point to understand these time related questions concerning PTC and TVS? Are there other solutions you can point me to? I have a bad market overview on what's available.
Best Answer
I don't think using normal PTC will give us a well predictable behavior. The thermal time constant given by datasheet is referred to zero-power conditions. Is behavior is determined by too much factors (ambient temperature, voltage applied, etc).
Why dont use a fuse? Maybe a resettable fuse (PPTC, I think you means this device in the question), that generally is little slow compared to fast-acting fuse, according to Littlefuse specification (see "Time-Current Characteristic").
Or better, why not an overvoltage crowbar?Some useful links about thermistors:
And about TVS, Littlefuse and Vishay sites are a good sources of informations.