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Pulling single supply OPA725 output to 0v with a negative supply and resistor

Mark Bridges
Intellectual 270 points
Other Parts Discussed in Thread: OPA725, OPA334, LM7705

Hello all, can you use a negative supply and resistor to pull the output of a OPA725 to 0v, when the part has a +12V supply?  I am referring to the same circuit as shown in figure 2 on page 8 of the OPA334 data sheet.  I would use the OPA334 but this circuit must operate off a +12V supply. 

If the OPA725 won't do this function, please recommend an op amp that will (one that can be made to go to 0v output but has a +12V supply).


Thanks for all responses.

  • 0
    Expert 2580 points

    Hi,

    perhaps the LM7705 is an option, giving the op amp a very small negative supply to get real Zero Output.

    With best regards

    Gerhard

  • 0 in reply to Gerhard Kreuzer
    TI__Guru 60570 points

    Mark,

    LM7705 (Negative Bias Generator) is in fact an option as long as the total sinking current is less than 20mA.  You may also try to use OPA725 and appropriatly sized pull-down resistor, Rpd, connected to a negatice supply, Vneg.  The resistor must be able to sink the entire quiescent current of the output stage which is typically ~50% of the total IQ.  Since in case of OPA725 the maximum IQ is 6mA, you must aim at sinking with the external Rpd around 3mA; thus with Vneg=-3V you must use Rpd=1k while Vneg=-12V would require Rpd=4k.