SLOA332 july   2023 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. 1Slew Rate Definition
    1. 1.1 Virtual Ground and Slew Rate
  5. 2Bipolar Op Amp Slew Rate Example
  6. 3CMOS 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. 4Four Methods to Determine Boost or No Boost Using the Data Sheet
  8. 5Slew Rate Dependencies on Circuit Signal Levels and Op Amp Gain Set by Feedback Network
  9. 6How Much Output Slew Rate is Needed to Support a Sine Wave or Other Non-step Inputs
  10. 7Stability Also Plays a Role in Observed Slew Rate
  11. 8Summary
  12. 9References

3 CMOS Op Amp Slew Rate Example

CMOS op amps replace NPN and PNP transistors with NMOS and PMOS transistors. The bias current split is based on voltage difference squared plus a linear factor. Therefore, expect some variation between different CMOS op amps. TLV9001 data is charted in Figure 3-1 up to 100 mV. The curve in Figure 3-1 looks similar to the bipolar example for VID. Most other CMOS amplifiers show similar behavior. Figure 3-1 is referenced throughout this application note, see Section 4 and Section 5.

GUID-20230509-SS0I-PRB6-Z3VG-CN8LHWZQK2XX-low.svgFigure 3-1 CMOS SR/SR[max] Versus VID

For the TLV9001, 100% of the maximum natural slew rate occurs with VID >> 100 mV. However, the internal bias current (B) and CC capacitor give 0.5 V/µs slew rate, not the 2 V/µs stated in the data sheet. The TLV9001 employs a slew boost circuit to raise the slew rate to 2 V/µs. Figure 3-1 is the natural slew rate based solely on bias current and compensation capacitance with the inactive boost circuit.