Input Protection of ADG5436

I use the ADG5436 in an application where it can happen that signals are applied to the analog inputs to the unpowered switch.
I want to ask if external schottky diodes to the supplies are recommended in such an application to protect the internal clamping diodes?
This common method for input protecting is described in the application note MT-088 on page 21. It is no problem in my application, if the input signal appears at the downstream circuitry, because the downstream circuitry has a high impedance. Unfortunately I can't use any of your power off protected switches because I need a SPDT configuration.

Regards,
Steffen

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  • +1
    •  Analog Employees 
    on Oct 7, 2011 1:37 PM

    Hi Steffan,

    While the ADG5436 is very robust from a latch-up and ESD transient view point, it is not fault protected. Analog inputs applied to the switch while unpowered may damage the switch if the current is not limited. As you can see from the Absolute Maximum Ratings section the analog inputs should be limited to 0.3V above the supplies or 30mA, whichever occurs first. This is due to the internal ESD protection diodes which may become forward biased under these conditions.

    You have two options here:

    1. You could use external components for protection such as schottkey diodes and current limiting resistors as you have suggested or...

    2. The second option is to use the ADG4613 and configure it externally to make a dual SPDT. The ADG4613 is a 4 x SPST with power off protection features, meaning analog signals may be applied to the switch with no power. This can be configured as an SPDT as follows:

    What is you application?
    Regards,
    Michael
Reply
  • +1
    •  Analog Employees 
    on Oct 7, 2011 1:37 PM

    Hi Steffan,

    While the ADG5436 is very robust from a latch-up and ESD transient view point, it is not fault protected. Analog inputs applied to the switch while unpowered may damage the switch if the current is not limited. As you can see from the Absolute Maximum Ratings section the analog inputs should be limited to 0.3V above the supplies or 30mA, whichever occurs first. This is due to the internal ESD protection diodes which may become forward biased under these conditions.

    You have two options here:

    1. You could use external components for protection such as schottkey diodes and current limiting resistors as you have suggested or...

    2. The second option is to use the ADG4613 and configure it externally to make a dual SPDT. The ADG4613 is a 4 x SPST with power off protection features, meaning analog signals may be applied to the switch with no power. This can be configured as an SPDT as follows:

    What is you application?
    Regards,
    Michael
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