logo elektroda
logo elektroda
X
logo elektroda

Rail-to-rail opamp output swing with Vdd=5V, Vss=-5V, inverting amp configuration

306 10
Best answers LABEL_AI_GENERATED

Will a rail-to-rail op-amp powered from +5 V and -5 V produce exactly the rail voltage in an inverting amplifier with a 1 V input and 1 kΩ/5 kΩ resistors, and what limits its output swing?

No: with a 1 V input and 1 kΩ/5 kΩ feedback network, the ideal inverting-amplifier output is -5 V, not +5 V, and a rail-to-rail op-amp still will not reach the rail exactly in real life because output swing depends on load current [#21684546][#21684543] The datasheet usually gives a graph of supply-to-output headroom versus output current, and that current includes both the external load and the feedback network current [#21684543][#21684545] You should pick resistor values by checking the acceptable rail distance in the datasheet, then use Ohm’s law to keep the total output current low enough for the required swing [#21684545] In general, rail-to-rail parts are useful because conventional op-amps often leave a large portion of the supply range unusable, especially in 3.3 V and 5 V systems [#21684549] In inverting configurations, input common-mode limits are usually less of a problem, but output-stage limits still apply [#21684543]
AI summary based on the discussion. May contain errors.
ADVERTISEMENT
  • Rail-to-rail output still limited by load and headroom

    #1 21684542
    Alexandru Radu
    Anonymous  
  • ADVERTISEMENT
  • Rail current limits reduce rail-to-rail output swing

    #2 21684543
    Richard Gabric
    Anonymous  
  • #3 21684544
    Alexandru Radu
    Anonymous  
  • ADVERTISEMENT
  • Use datasheet output swing versus load current

    #4 21684545
    Richard Gabric
    Anonymous  
  • ADVERTISEMENT
  • #5 21684546
    Richard Gabric
    Anonymous  
  • ADVERTISEMENT
  • #6 21684547
    Alexandru Radu
    Anonymous  
  • #7 21684548
    Alexandru Radu
    Anonymous  
  • Need for rail-to-rail op-amps in low-voltage systems

    #8 21684549
    Richard Gabric
    Anonymous  
  • Open-loop gain simulation method needed

    #9 21684550
    Alexandru Radu
    Anonymous  
  • #10 21684551
    nani sandy
    Anonymous  
  • Simple op amp models omit input and output stages

    #11 21684552
    Richard Gabric
    Anonymous  

Topic summary

LABEL_AI_GENERATED
The discussion focuses on the output swing capabilities of rail-to-rail (RR) operational amplifiers (opamps) powered by ±5 V supplies in an inverting amplifier configuration. It clarifies that while RR opamps can approach the supply rails more closely than conventional opamps, the output cannot be assumed to reach the rails exactly due to limitations imposed by load current and feedback network currents. Datasheets typically provide graphs showing output voltage versus load current, which are essential for selecting appropriate resistor values to maintain desired output swing. The input stage topology and output stage design (e.g., use of charge pumps or dual differential inputs) affect offset voltages, input common-mode range, and output swing. The benefit of RR opamps is highlighted in low-voltage systems (3.3 V or 5 V) where maximizing dynamic range is critical, such as buffering ADC inputs. Simulation challenges in modeling open-loop gain are noted, emphasizing the need for accurate device models that include input/output stage behavior and saturation effects. Users are advised to consult datasheets and manufacturer application notes for detailed performance characteristics and to design with realistic load and bias conditions.
AI summary based on the discussion. May contain errors.
ADVERTISEMENT