SBOS784C November   2016  – January 2019

PRODUCTION DATA.

1. Features
2. Applications
3. Description
4. Revision History
5. Device Comparison Table
6. Pin Configuration and Functions
7. Specifications
8. Detailed Description
1. 8.1 Overview
2. 8.2 Functional Block Diagram
3. 8.3 Feature Description
4. 8.4 Device Functional Modes
9. Application and Implementation
1. 9.1 Application Information
2. 9.2 Typical Application
10. 10Power Supply Recommendations
11. 11Layout
12. 12Device and Documentation Support
1. 12.1 Device Support
1. 12.1.1 Third-Party Products Disclaimer
2. 12.1.2 Development Support
2. 12.2 Documentation Support
5. 12.5 Community Resources
7. 12.7 Electrostatic Discharge Caution
8. 12.8 Glossary
13. 13Mechanical, Packaging, and Orderable Information

• D|8
• DCK|5
• DBV|5
• D|8
• DCK|5

#### 9.2.2 Detailed Design Procedure

Figure 29 shows a unity-gain buffer driving a capacitive load. Equation 1 shows the transfer function for the circuit in Figure 29.Figure 29 does not show the open-loop output resistance of the operational amplifier (Ro).

Equation 1.

The transfer function in Equation 1 has a pole and a zero. The frequency of the pole (fp) is determined by (Ro + RISO) and CLOAD. The RISO and CLOAD components determine the frequency of the zero (fz). A stable system is obtained by selecting RISO so that the rate of closure (ROC) between the open-loop gain (AOL) and 1/β is 20 dB per decade. Figure 30 shows the concept. The 1/β curve for a unity-gain buffer is 0 dB.

Typically, ROC stability analysis is simulated. The validity of the analysis depends on multiple factors, especially the accurate modeling of Ro. In addition to simulating the ROC, a robust stability analysis includes a measurement of overshoot percentage and AC gain peaking of the circuit using a function generator, oscilloscope, and gain and phase analyzer. Phase margin is then calculated from these measurements. Table 3 shows the overshoot percentage and AC gain peaking that correspond to phase margins of 45° and 60°. For more details on this design and other alternative devices that can replace the TLVx172, see the Capacitive Load Drive Solution Using an Isolation Resistor precision design.

### Table 3. Phase Margin versus Overshoot and AC Gain Peaking

PHASE MARGIN OVERSHOOT AC GAIN PEAKING
45° 23.3% 2.35 dB
60° 8.8% 0.28 dB