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MUX36S08: MUX36S08 input protection

Part Number: MUX36S08

With a +/-10V supply to the MUX36S08 and analog input that can occasionally reach +/-25V, what type of input protection circuitry would be recommended ?  Is a series current limiting resistor (e.g. 5K) sufficient ?

The Data Sheet seems to indicate that the analog inputs can extend 2 volts beyond the rails without damage, from which I infer that there might -not- be internal, reverse biased diodes to the rails to protect the inputs. If this supposition is correct, then a current limiting resistor might not be sufficient and I might therefore need to implement my own (external) reversed biased diodes to the rails to protect the analog inputs (which would be a lot of extra parts for eight inputs ...)

The Data Sheet doesn't seem to include any information on input protection (or at least I couldn't find it) ....

Perhaps the internal reversed biased diodes were omitted to limited the leakage current ???  Or perhaps I'm just misinterpreting the Data Sheet ...

Thanks !

  • Hi Scott,

    In your case, I would recommend two external circuitry.

    1. As you suggested, a current limiting resistor in front of MUX36S08 input. Assume in your system,

    VDD =15V, Vin = 25V, Current limiting Resistor, R = 5KOhms

    Thus, the potential current is calculated as (25V - 15V)/5KOhms = 2mA.

    In terms of input current magnitude, 2mA is relatively small and can bearly damage the device input pin.
    In terms of the input voltage now, it is 25V - 2mA * 5KOhms = 15V, which is less than VDD. It compiles data sheet.

    2. If bandwidth is not a concern, external capacitors can be added at the MUX36S08 analog input pins. It can further limit your 25V transient effect.

    3. TVS diode is also recommended because I assume you have IEC ESD requirements. MUX36S08 is the first stage of your analog signal chain, while the device itself does not have IEC ESD protection capability.