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LM8262: input terminal diode-clamp

Kai Nomiyama
Expert 5285 points
Part Number: LM8262
Other Parts Discussed in Thread: LM8272, OPA2322

Hi Team,

Can LM8262 support below comment?

"Input terminals are diode-clamped to the power-supply rails. Input signals that can swing more than 0.3 V beyond the supply rails should be current limited to 10 mA or less."

We can apply LM8272 simplified schematic as LM8262 schmatic and it doesn't have clamp diode to VDD so I thinnk LM8262 does not support above comment.

Regards,

Kai

  • 0
    TI__Guru*** 140026 points

    Hello Kai-san,

    LM8272 simplified schematic should be close to LM8262 ; both have input to input diodes , both are bipolar.

    Yes, input current must be limited. The lower the current the better. During this beyond 0.3V of rail, the output may not be correct. Phase reversal may occur.  

  • 0 in reply to Ron Michallick
    Guru 243220 points

    The LM8262's absolute maximum ratings allow to go 0.8 V beyond the rails, so there is some difference.

  • 0 in reply to Clemens Ladisch
    TI__Guru*** 140026 points

    Kai-san, Clemens

    Here is voltage sweep of input pins where input current is measured. Both power supply pins were 0V.

     

    LM826X has higher resistance for negative voltage.  

  • 0 in reply to Ron Michallick
    TI__Expert 5285 points

    Hi Ron,

    I refered OPA2322 datasheet comment so I reused 0.3V in my question but actual my question is that LM8262 can swing more than 0.8 V beyond the supply rails should be current limited to 10 mA or less?

    From below e2e, if we limit input current, we don’t need to limit the input voltage. Internal clamp diodes are safe to ±10mA.
    That internal clamp diodes clamp input to V+/-.

    Protecting Inputs from Damage— EOS - The Signal - Archives - TI E2E support forums

    On the other hand, When we take a look at LM826x, there is no internal clamp diodes to V+/- from LM8272 simplified schematic so I asked we can refer the same comment to LM8262 or not.

    Regards,
    Kai

  • 0 in reply to Kai Nomiyama
    TI__Guru*** 140026 points

    Kai,

    Which would be easier for the application to control, voltage at input or current into input?

    Simplified schematic means that not everything is included. 

  • 0 in reply to Ron Michallick
    TI__Expert 5285 points

    Hi Ron,

    in order to follow below comment, current into input is easier for the application to control.
    If we can say that LM8262 support below comment or similar comment, I close this thread.
    "can LM8262 swing more than 0.8 V beyond the supply rails should be current limited to 10 mA or less?"

    Regards,

    Kai

  • 0 in reply to Kai Nomiyama
    TI__Guru*** 140026 points

    Kai,

    The official limitation is 0.8V beyond rail. No current is specified. This way of defining the limitation was common in the past. This past method is not very practical or the best way to protect a "diode". The widely known general rule of the past was to limit current to 10mA ; this is practical advice. Some newer data sheets state a 10mA current. I personally recommend 1mA because it is 1/10th the ABS MAX stress and usually easy to implement.

    If a official current is needed, then I'll have to recommend a different op amp that has a current value stated in the data sheet.