SLOA277B january   2019  – july 2023 LM124 , LM124-N , LM124A , LM158 , LM158-N , LM158A , LM224 , LM224-N , LM224A , LM258 , LM258-N , LM258A , LM2902 , LM2902-N , LM2902-Q1 , LM2902K , LM2902KAV , LM2904 , LM2904-N , LM2904-Q1 , LM2904B , LM2904B-Q1 , LM2904BA , LM321 , LM324 , LM324-N , LM324A , LM358 , LM358-N , LM358A , LM358B , LM358BA , TS321 , TS321-Q1

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Devices Covered in Application Note
    1. 1.1 Common Schematic
    2. 1.2 Base Part Numbers
    3. 1.3 Input Voltage Offset Grades
    4. 1.4 Maximum Supply Voltage
    5. 1.5 High Reliability Options
    6. 1.6 HBM ESD Grade
    7. 1.7 LM358B, LM358BA, LM2904B, LM2904BA, LM324B, LM2902B
  5. 2Input Stage Considerations
    1. 2.1 Input Stage Schematic
    2. 2.2 Input Common Mode Range
    3. 2.3 Input Impedance
    4. 2.4 Phase Reversal
  6. 3Output Stage Considerations
    1. 3.1 Output Stage Schematic, VOL and IOL
    2. 3.2 IOL and Common Mode Voltage
    3. 3.3 Output Stage Schematic, VOH and IOH
    4. 3.4 Short Circuit Sourcing Current
    5. 3.5 Output Voltage Limitations
  7. 4AC Performance
    1. 4.1 Slew Rate and Bandwidth
    2. 4.2 Slew Rate Variability
    3. 4.3 Output Crossover Time Delay
    4. 4.4 First Crossover Example
    5. 4.5 Second Crossover Example
  8. 5Low VCC Guidance
    1. 5.1 Low VCC Input Range Supporting –40°C
    2. 5.2 Low VCC Output Range Supporting –40°C
    3. 5.3 Low VCC Audio Amplifier Example
  9. 6Comparator Usage
    1. 6.1 Op Amp Limitations
    2. 6.2 Input and Output Voltage Ranges
    3. 6.3 Overload Recovery
    4. 6.4 Slew Rate
  10. 7Unused Amp Connections and Inputs Connected Directly to Ground
    1. 7.1 Do Not Connect Inputs Directly to Ground
    2. 7.2 Unused Amplifier Connections
  11. 8Conclusion
  12. 9Revision History

3.3 Output Stage Schematic, VOH and IOH

Unlike most new op amps that have a rail-to-rail output, this family of op amps has a high level output voltage that is significantly lower than the VCC power rail, regardless of the load sourcing current. Figure 3-4 shows the Darlington NPN transistors that provide sourcing current. An active current limiter helps protect the op amp and load from overcurrent conditions.

GUID-C8EC1890-4906-44FB-82D8-F940911FC58E-low.gifFigure 3-4 Schematic of Output Driver Stage with Highlighted Source Driver and Current Limiter

The Darlington NPN provides a low output impedance and the base current flows to the output load for higher efficiency. This setup has a high headroom requirement that significantly reduces the VOH level. The two base emitter junctions in the Darlington NPN have a combined temperature coefficient of approximately –4 mV/°C. Therefore VOH has an equal and opposite temperature coefficient of 4 mV/°C. Per the data sheet Electrical Characteristics tables, the VOH level is VCC – 1.5 V or better with a 2-kΩ load to ground when VCC is 5 V at 25°C; this is 1.75 mA. The typical VOH level varies with load current and also varies with temperature as seen in Figure 3-5. VOH performance relative to VCC is independent of VCC, which means the set of curves in Figure 3-5 apply to the entire operating range of VCC.

GUID-E316D916-C62F-4098-BFA8-EEC578A53A93-low.gifFigure 3-5 Plot Showing VOH Relative to VCC (VOH - VCC) vs Load Current (IOH)