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OPA2192: What circuit condition "No load" mean

Part Number: OPA2192
Other Parts Discussed in Thread: OPA192

Hi,

I am confirming datasheet of OPA2192, then I found following spec.

I wonder why saturation voltage is observed in case of "No load".

I believe that this voltage depends on output current (I think that we expect 0mV in this condition). Does it mean leakage ?

Could you please tell me why output swing from rail is NOT 0mV in case of "No load" ?

Best Regards,

Machida

 

  • Hello Machida,

    There is no op amp that allows true swing all the way to the rail.  Even the best rail-to-rail output stage will have some small level limitation (in the millivolts). It is important to realize that there will always be some bias current flowing in the output stage, even if no load is connected.  Normally this is about 1/2 the quiescent current (IQ) of the amplifier.  Another consideration is the MOSFET characteristic curve.  For very low drain current, VDS can be very low, but will never be zero. That minimum VDS is what sets the output swing limitation.  Also bare in mind that the characteristic table show on that table is a slam limit not linear output swing. 

    Best,

    Errol Leon

    Texas Instruments

    Precision Op Amp Applications

  • Hi Leon-san,

    Thank you for your reply.

    I understood about current source in case of "No Load".

    BR,

    Machida

     

  • Leon-san,

    I have one additional question.

    If user use single supply, this "voltage output swing from rail" spec is applied for only Vcc(not applied for GND), right  ?

     Best Regards,

  • Machida-san,

    The spec is applied to both positive and negative rails.  For the negative rail (with no load), the output swing is 5mV (typical) away from the negative rail (ground) for OPA2192.

    Best,

    Errol

  • Machida-san,

    Adding to Errol's response, if you are interested only in the linear output swing of OPA192, where the output maintains high open-loop gain, you must look at the condition column used to measure the open-loop gain, AOL - see below.  In the case of no load condition, I would estimate the linear output swing to be within 100mV from either rail but unlike the other two loads shown below it is not tested in production.

  • Hi Leon-san,

    I understood case of single supply as well.

     Hi Lis-san,

    Thank you for your reply.

    if you are interested only in the linear output swing of OPA192, where the output maintains high open-loop gain,

    Yes, I am also concerned about above. Thank you for sending comment !

    According to your comment, I understood as shown below in case of No Load.

    Best Regards,