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LMV796-Q1: LMV796 Injection Current

Part Number: LMV796-Q1
Other Parts Discussed in Thread: LMV796, OPA365-Q1

Dear team,

please help with below:

Is it possible to use LMV796-Q1 with input voltage of (V+) +0,3V and/or (V-) -0,3V ?

I would expect this comes down to the allowed injection current of the input clamps!?

What is the allowed voltage TI would allow?

What is valid for the to inputs to each other?

Thanks,

Matt

  • Former Member
    0 Former Member

    Hi Matt,

    From the top of page 2 of the datasheet's "Absolute Maximum Ratings" section, it's possible to exceed the supplies by 300mV.  Please note that if this specification is violated, you may damage the part as the specification is an absolute maximum.  Also, make sure to not accidentally violate any of the other specifications, such as the Vin Differential specification two lines higher up which should answer your last question.

    I'm not familiar enough with the part's input structure to tell you exactly what is going on.  But yes, these input specifications are usually set to avoid damaging the input of the part and often involve exceeding some kind of a limit on a clamp.  Exceeding these limits may short a part of the input structure out leading to a damaged part.

    Regards,

    Daniel

  • Dear Dan,

    above does not answer our question.

    We understand that abs max can not be exceeded , but please check with design team on the input protection and the max injection current that LMV796 can withstand.

    It is critical to understand to ensure usage of the part in case input voltage exceeds the rated input ratings - per our understanding this can be tolerated when the max currents are known and power can be calculated.

    Could you please verify with design team?

    Many thanks,

    Matt

  • Matt,

    The practical limit is based on current, not voltage. The old school general rule for op amps was 'up to 10mA was safe'. The new general rule is 1mA is safe for continuous use and 10mA for rare events. Nevertheless this is not covered by the data sheet claims.

  • Dear Ron,

    thanks for your comment.

    Could you please clarify: is the 1mA per Input?

    What is the max injection current we could allow with LMV796-Q1?

    Is there another component with similar specification that allows higher voltage vs V+/V- as LMV796-Q1?

    Many thanks,

    Matt

  • Matt,

    Is there a reason that you can't reduce the level of the device abuse?  Voltage beyond the rails doesn't produce linear operation in the op amp. It would be better to reduce the input voltage or add external diodes to limit voltage.

  • Former Member
    0 Former Member in reply to 5t34m

    Matt,

    If you would like to look at alternative parts, consider OPA365-Q1.  It has higher performance and allows you to exceed the rails by 500mV instead of 300mV.  Please note that it does come with an elevated cost.  I would recommend following Ron's advice, if at all possible.

    Regards,

    Daniel

  • Matt,

    1mA per input pin is not very stressful. The estimated current is I = (V - 0.3V) / R  where V is the absolute voltage beyond the power supply rails.

  • Sometimes, a fix is to limit that input current with a defined series input R and then add external shunting Schottkies to the supplies to divert what you are calling an injection current away from the internal ESD steering diode - there is also a max differential voltage spec where you could divert that current with back to back diodes. In high speed we use the BAV99 for that kind of thing.