• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 2 answers
  • Subscribers 49 subscribers
  • Views 474 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

OPA836: How to treat unuse FBx pin on OPA836

Jason Dai
Expert 3720 points
Part Number: OPA836

Hello E2E,

How to treat unuse FBx pin on OPA836?

~Jason

  • 0
    TI__Genius 11585 points

    Hi Jason,

    I reviewed a section on the OPA836 datasheet, section 9.1.8 (page 34-35), which references how to treat the FBx pins on the OPA836.  It appears the simplest setup, which you may be referring to when you mention the 'unused' FBx pin, requires the modification of shorting pin 1 to pin 9.  This results in a non-inverting gain of 1 V/V.  The tables referenced include various configurations and gains.

    If you have a more specific use case, possibly one where it is unclear how to treat the FBx pins, please elaborate and respond.

    Best Regards,

    Alec Saebeler

  • 0 in reply to Alec Saebeler
    TI__Expert 3720 points

    Alec,

    If customer wants to configure OPA836 as buffer, which connection in table 3 and 4 should we follow?

    Should we refer to connection as gain=1v/v? if so, how to treat pin 2?

     

    ~Jason

  • 0 in reply to Jason Dai
    TI__Genius 11585 points

    Hello Jason,

    Great question: for a unity-gain buffer configuration with noninverting input, as you mentioned, the desired configuration is to short pin 1 (output) to 9 (FB1) for a 1V/V noninverting gain.  Also, for unity-gain buffers you will want to wire/short the inverting input (pin 2) to the output (pin 1).  This is specific to the unity-gain buffer case, as gains of >1 will necessitate a feedback network between the inverting input and op-amp output.  If the customer is not implementing the power down feature, the PD pin (pin 4) should be wired to positive supply (V_s_+).  If the customer intends to use the power down functionality, I would advise to always drive the PD pin, and never let it float.  You may float the remaining FB2-FB4 pins (pins 6,7,8), as my understanding is they need only be connected when intended to be in use.

    In addition to properly wiring the op-amp, including the Power Down pin (pin 4), you would also want to advise the customer to be aware of input common mode and output limitations.  Since the OPA836 is a Rail-to-rail op-amp, the output voltage can swing quite close to the supply rails, within 200mV of either supply.  Additionally, an a 5V single-supply configuration the OPA836 can operate within an input range of -0.2V - 3.9V.  While these limits are generous, if the customer has a specific set of supply, input signal, and output load conditions they are designing around, they should review the datasheet for advice on the best method of operating the OPA836 to achieve the desired results.  

    I hope this helps with the customer design.

    Best,

    Alec