ZHCSIQ4B September   2018  – December 2018

PRODUCTION DATA.

1. 特性
2. 应用
3. 说明
1.     Device Images
4. 修订历史记录
5. Pin Configuration and Functions
6. Specifications
7. Detailed Description
1. 7.1 Overview
2. 7.2 Functional Block Diagram
3. 7.3 Feature Description
4. 7.4 Device Functional Modes
8. Application and Implementation
1. 8.1 Application Information
2. 8.2 Typical Applications
1. 8.2.1 Typical Application: SAR ADC Driver
2. 8.2.2 Typical Application: Low-Pass Filter
9. Power Supply Recommendations
10. 10Layout
11. 11器件和文档支持
1. 11.1 器件支持
2. 11.2 文档支持
3. 11.3 接收文档更新通知
4. 11.4 社区资源
5. 11.5 商标
6. 11.6 静电放电警告
7. 11.7 术语表
12. 12机械、封装和可订购信息

• D|8

#### 7.3.6 Capacitive Load and Stability

Figure 48 shows the total circuit noise for varying source impedances with the operational amplifier in a unity-gain configuration (with no feedback resistor network and therefore no additional noise contributions). The OPA828 and OPA211 are shown with total circuit noise calculated. The op amp itself contributes both a voltage noise component and a current noise component. The voltage noise is commonly modeled as a time-varying component of the offset voltage. The current noise is modeled as the time-varying component of the input bias current and reacts with the source resistance to create a voltage component of noise. Therefore, the lowest noise op amp for a given application depends on the source impedance. For low source impedance, current noise is negligible, and voltage noise generally dominates. The OPA828 device has both low voltage noise and extremely low current noise because of the FET input of the op amp. As a result, the current noise contribution of the OPA828 is negligible for any practical source impedance, which makes it the better choice for applications with high source impedance.

The equation in shows the calculation of the total circuit noise, with these parameters:

• en = voltage noise
• In = current noise
• RS = source impedance
• k = Boltzmann's constant = 1.38 × 10–23 J/K
• T = temperature in degrees Kelvin (K)