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

4.2 Slew Rate Variability

It is best to allow for some margin between the application's slew rate requirement and the typical slew rate of the device used. Normal process variance affects internal bias currents and capacitor oxide thickness, which are two factors that determine slew rate. These components are highlighted in blue in Figure 4-1. There may also be a slight difference between the positive and negative slew rates. The reason for this difference is simple: the transistor in the red box in Figure 4-1 has no turn off drive. The NPN transistor driving the red box transistor can only source current to turn on, but cannot sink current to turn off. The base to collector capacitance of the transistor in the red box in this device family varies among the dies in production. The beta of the NPN transistor is also a factor in determining slew rate. If the natural turn off slew rate of the red boxed transistor

SR Natural   =   100   µA β NPN   ×   Cap CB

is slower than the slew rate set by the bias and compensation capacitor

SR Comp   =   6   µA Cap Comp

then the positive slew rate is reduced while the negative slew rate is not affected. Hence, the positive slew rate can be slower than the negative slew rate. LM358B, LM2904B, LM324B, and LM2902B have a discharge path for the base of the red boxed transistor. Therefore, the slew rate is not affected by this highlighted transistor.

GUID-AC1A49E0-E906-414D-AE88-60AB46B25AFB-low.gif Figure 4-1 Schematic With the Following Slew Rate Components Highlighted: Tail Current (Blue), Compensation Capacitor (Blue), Collector Current (Green), Collector to Base Capacitance (Red)

Only the commercial grade quad op amp with the widest input offset specification has a die with enough base-collector capacitance to typically demonstrate variation in high temperature slew rates. Slew rate differing in all other device variants will be a rare occurrence. The key point is not to depend on matching slew rate. Fortunately, few circuits actually require matching slew rate. For reference, the slew rate curves of two common devices are shown below with the commercial grade in Figure 4-2 and the automotive grade in Figure 4-3. Note that the other die designs typically have matching positive and negative slew rates. A small percentage of samples may exhibit some differences at high temperature.

GUID-952DE4CC-5861-456F-BC3F-C28E422577D0-low.gifFigure 4-2 Plot Showing Slew Rate vs Temperature for LM2902DR
GUID-90D284C6-F202-4A21-90F8-A36A96116240-low.gifFigure 4-3 Slew Rate vs Temperature for LM2902QDRQ1