Problem with ADG1606 protection

Question

Hello, 
 We use an ADG1606 MUX as the final stage of our circuit to connect to external units (Hot unplug condition is normal in our application). From datasheet, I understood that "Overvoltages at IN, S, or D are clamped by internal diodes. Current should be limited to the maximum ratings given" and from engineerzone I know that ADG1606 is protected against ESD. 
 We have implemented following items as protection for the MUX (Our switch is powered from a single supply): 
 1- A blocking 1N4148 diode is placed in series with supply to VDD pin. (The circuit is not subjected to negative voltages and we eliminated blocking diode in GND side.) 
 2- A current limiter circuit is implemented in D channel and prevents currents above 60mA to pass S channels to D channel (S->D). (D ->S is under control and over-current is not possible.) 
 Before we implement protection methods above, we had different kinds of failures, but recently we had only one type of failure (It is rare, but it happens); A single channel is shortened to GND. It seems an INTERNAL Zener diode of channel is burnt out and the result is short-circuit to GND. If the MUX is protected against over-voltage, why does it happen? What is the solution? 
 Look forward to your reply, 
 Best regards

JCreech · Accepted Answer

HI imanjohn, 
 If you prefer the second option you must also ensure that the voltage on the pin does not exceed the voltage max ratings. It may be best to use the current limiter with a Schottky diode to ensure both over current and over voltage requirements are met. 
 ADI also do a range of over voltage suppression parts (the ADG465 and ADG476) which may be of use in the application, as they will ensure that signal is within defined rails. I have attached the data sheets for your consideration. 
 Regards, 
 Joe)

JCreech · Answer

Hi imanjohn, 
 Have you any more details on what the fault is that is damaging the part? Is it a positive or negative over voltage condition? 
 I have attached a tutorial which outlines protection methods to be used. You have implemented one of them but you should note that it is important to verify that the protection method used is acceptable for all possible errors the part can be subjected to. 
 The ADG1606 data sheet states that the ADG1606 analog inputs have a max rating of 30mA in an over voltage condition (Vdd+0.3V) and so the 60 mA limit you mentioned below is too high for this case. 
 If you have any further questions, let me know. 
 Regards, 
 Joe

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Problem with ADG1606 protection