SLOA332A July   2023  – September 2024 LMV821-N , LMV831 , OPA2991 , OPA345 , OPA376 , OPA376-Q1 , OPA377 , OPA377-Q1 , OPA4991 , OPA991 , TL074 , TLV376 , TLV9001 , TLV9002 , TS321

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1 Slew Rate Definition
    1. 1.1 Virtual Ground and Slew Rate
  5. 2 Bipolar Op Amp Slew Rate Example
  6. 3 CMOS Op Amp Slew Rate Example
    1. 3.1 Slew Boost Example 1
    2. 3.2 Slew Boost Example 2
    3. 3.3 Slew Boost Summary
  7. 4 Four Methods to Determine Boost or No Boost Using the Data Sheet
    1. 4.1 Method 1: Compare Slew Rate Versus Gain Bandwidth
    2. 4.2 Method 2: Compare Quiescent Current Versus Similar SR Devices
    3. 4.3 Method 3: Evaluate Large Signal Response
    4. 4.4 Method 4: Evaluate Small Signal Response
  8. 5 Slew Rate Dependencies on Circuit Signal Levels and Op Amp Gain Set by Feedback Network
  9. 6 How Much Output Slew Rate is Needed to Support a Sine Wave or Other Non-step Inputs
  10. 7 Stability Also Plays a Role in Observed Slew Rate
  11. 8 Summary
  12. 9 References
  13. 10Revision History

Abstract

This application note discusses the discrepancy between the slew rate in applications and the slew rate specifications in op amp data sheets. The virtual ground (or virtual zero) concept simplifies op amp design by assuming the voltage difference between the inputs, VID, is zero. VID must increase to generate slew rate. Just over 100mV are needed to reach the maximum natural slew rate that is listed in many data sheets. Some op amps have a data sheet slew rate greater than natural slew rate by incorporating a slew boost circuit. The VID needed to reach boosted slew rate can be several hundreds of millivolts. Most data sheets do not state the presence of slew boost; however, there are methods to determine the presence of slew boost by examining the data sheet figures with waveforms.