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OPA316, level shift input signal, buffer output

VT
Genius 3300 points
Other Parts Discussed in Thread: OPA316, TIPD154, OPA317

1. I have application where input signal voltage varies from +5V to -5V. Have to level shift the signal and fed it to microcontroller adc which is sampling at 1MSPS. Microcontroller adc range varies from 0V to 3.3V

2. Selected OPA316 for this application. Attached find the circuit.
Can I level shift the signal using single supply opamp(3.3V) volt from +-5V to 0-3.3Vdc

3362.Design1.pdf

  • 0
    TI__Intellectual 2155 points

    Hi Vindhyachal,

    The voltage on your +IN pin on the OPA316 ranges from -1.25V to +1.25V. If the OPA316 is operated in single supply mode, the negative input range will be ignored and the OPA316 will simply output 0V for this entire input voltage range.

    You might find the TIPD154 reference design interesting for your application. It uses an OPA317 (you could replace this with an OPA316) to attenuate and level shift a bipolar +/-5V signal to a 0-3.3V signal for an ADC input.

    Please let me know if you have any more questions!

    Regards,

    Mihir Gupta

    Field Applications Engineer

    Texas Instruments

  • 0 in reply to Mihir Gupta65
    Genius 3300 points

    Hi Mihir,

    Is attached updated circuit ok? I think it should level shift +-5V signal to 0-3.3V dc using single supply opamp.

    2451.Design1.pdf

  • 0 in reply to VT
    TI__Intellectual 2155 points

    Hello Vindhyachal,

    Please take a look at the attached schematic. It should do the job.

    sbom887.tsc

    You can use the design guide in the TI Reference design that I linked to above to understand how the circuit works.

    Regards,

    Mihir

  • 0 in reply to Mihir Gupta65
    Genius 3300 points
    Hi Mihir,

    Thanks for providing the circuit.
    Is circuit provided by me in post#3 not correct or it will also work? As I have already ordered its pcb design.
  • 0 in reply to VT
    TI__Intellectual 2155 points
    The circuit in Post 3 will work, but I recommend changing R4 to 1kOhm, since the settling time becomes too long with a 10kOhm resistor

    Regards,
    Mihir
  • 0 in reply to Mihir Gupta65
    Genius 3300 points
    Hi Mihir,

    This ckt works. But it has one major consideration that source voltage should be able to both source & sink current.
    Let say I have a sensor which is not able to sink current like theromocouple. Suppose I have sensor with +-5V & it dont sink current.
    In that case what would be the ideal solution?
  • 0 in reply to VT
    TI__Intellectual 2155 points

    Hi Vindhyachal,

    you are correct when you say that a thermocouple cannot sink or source any significant amount of current, since the I2R losses through the thermocouple will heat up your thermocouple and significantly affect your temperature measurement. In this case you have two options:

    1. First buffer the output of your thermocouple and then feed it to a level shifter circuit.

    2. Use an instrumentation amplifier and then feed the level shift voltage to the reference pin of the instrumentation amplifier.

    Have a look at this document that covers thermocouple signal conditioning circuits. You might find it interesting.

    Regards,

    Mihir