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THS4631: Input protection diodes

Frederic Cartieaux
Prodigy 10 points
Part Number: THS4631

Tool/software:

Hello,

I can see in the previous threads that this question has been asked before, but the answer has been sent by mail to the requester.

So I ask again : on the THS4631, are they some protection diodes on inputs, to protect against over-voltage ? What is the maximum current sustainable ?

I thank you in advance.

  • 0
    TI__Mastermind 20827 points

    Hello Frederic,

    There is input protection diode circuitry on the inputs for overvoltage protection.

    Your question on maximum current must be answered by selecting a scenario: instantaneous, transient current, current pulse, continuous current, etc.  Generally these diodes are rated for a smaller continuous current, but they can handle a larger current for transient conditions.

    Would you be able to share more about your application and circuit?

    Best,

    Alec

  • 0 in reply to Alec Saebeler
    Prodigy 10 points

    Hello Alec,

    I cannot share with you the exact schematic. The THS4631 OpAmp is used as a Schmitt trigger, with a 22kOhms in series on the inverting input.

    There is a risk in the application that a 28V is applied on the 22kOhms input resistance. The OpAmp shall be powered with +/-15V rails. This 28V can last for several minutes (so continuously).

    If there is an integrated protection diode, the clamping current should be 0.59mA ( =(28-15)/22000).

    Is that acceptable ?

    Best regards,

    Frédéric

  • 0 in reply to Frederic Cartieaux
    TI__Mastermind 20827 points

    Hello Frédéric,

    Thank you for sharing what you are able to share.  I can also connect with you privately so you may email me supporting material if you would like to do so.

    To confirm my understanding: there is a possibility of 28V present at the inputs, which would be across the 22kOhms of input impedance.  This voltage is considered a steady-state (continuous) signal for several minutes.

    Are you able to consider any adjustments or changes to your design?  Generally for high-speed amplifiers the input protection ESD diodes internal to the devices are sized to be as small as possible while being able to protect the amplifier.  The trade-off of a larger ESD cell could effect AC performance in other specifications, which is why ESD diodes internal to the device are typically lower-rated for continuous current.

    Would you be able to add external protection circuitry to your system design?  

    Is the 28V condition a known/acceptable condition for the circuit, or is this a glitch or unwanted signal which you have observed to occur?

    Best,

    Alec

  • 0 in reply to Alec Saebeler
    Prodigy 10 points

    Hello Alec,

    Ok in this case, let us connect by email.

    Best regards,

    Frédéric

  • 0 in reply to Frederic Cartieaux
    TI__Mastermind 20827 points

    Hello Frédéric,

    I have sent you a message request here on the e2e forum.  Please accept and I can share my email with you so you may share the information.

    Best,

    Alec

  • 0 in reply to Alec Saebeler
    TI__Mastermind 20827 points

    Hello Frédéric,

    The input protection diodes of the THS4631 can handle small continuous currents.  I can verify the input protection can handle the ~1mA or less current that you have proposed.

    You may proceed with your design understanding that the input protection diodes will handle ~1mA continuously.  I cannot disclose the actual limit & values here, but the application will work as you have described it to me.

    Best,

    Alec

  • 0 in reply to Alec Saebeler
    Prodigy 10 points

    Hello Alec,

    Thank you for your feedback !

    Best regards,

    Frédéric