I am working on Truck OBD communication systems.
I designed a prototype card and used ADG1406 for get communication with Truck's different communication pins. I added "multiple TVS"s for protect to MUX's pins.
I use battery voltage 24V for ADG1406's Vcc.
One of the truck pin has 24V voltage. It is not battery voltage pin. And also it is not communication pin. I don't know purpose of that pin.
When the vehicle's ignition is off, that pin stays 0V.
When the vehicle's ignition is on, that pin jumps 24V.
I tried two methods:
1-)While ignition is off, i plug the card to OBD socket "then i open the ignition" and i don't have any problem.
2-)While ignition is on, i plug the card to OBD socket and that pin burn the ADG1406's connected switch pin. After that ADG1406 doesn't work anymore and warming up fastly.
I designed new card and i added "resettable PTC fuse" to that pin.
While ignition is on, i plug the new card to OBD socket and that pin burn the ADG1406's connected switch pin and PTC fuse activated. After that ADG1406 works except that pin.
In datasheet, it says:
"ICs capable of 33 V operation"
So what is the problem?