• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 49 subscribers
  • Views 473 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LM8272: Structure check

Roy Chou1
Genius 16980 points

Part Number: LM8272

Team,

Can you let me know if below connection is ok or not?

Roy

  • 0
    Guru 140200 points

    Hi Roy,

    the left OPAmp is working properly. But the right OPAmp cannot go with the output all the way to -5V. But you could connect the +input of right OPAmp to the output of left OPAmp.

    Another issue is the high input bias current. of LM8272. 2µA across 8k (10k and 40k2 in parallel) gives an additional offset voltage of 16mV.

    Kai

  • 0 in reply to kai klaas69
    TI__Genius 16980 points

    Hi Kai,

    Thanks for your kindly comments! To be cleared, pin6 and pin7 should be disconnected, right? Can we floating pin5, pin6, pin7 to disable right OPAmp?

    Roy

  • 0 in reply to Roy Chou1
    TI__Mastermind 33723 points

    Hey Roy,

    For unused op amps, the recommended configuration is buffer configuration, not floating so you can assure the op amp is in the linear range. You can find more information on this here. If this is a new design, is there a particular reason you are looking at the LM8272? You can also use a single channel device and not worry about unused connections (as well as a lower input bias current to fix any offset voltage issues from input bias current). If you are interested in a newer device I'd be happy to help you find an alternative!

    The issue you will run into with the unused amp is that the input is rail to rail but the output lower limit is approximately 250mV from V- (per the datasheet). Having your inverting and noninverting terminals at different voltages will force the op amp to try to correct this and may cause excess current consumption. As per the app note linked above, the recommended connection in this case is a resistor divider on the non-inverting terminal of the op amp.

    I agree with Kai's comments on the other op amp. 

    Best,
    Jerry