ALCL-13-5 380-500V 用于系统高压变频器

ALCL-13-5 380-500V 用于系统高压变频器 

将PD引脚连接到低电平将禁用放大器，并将输出置于高阻抗状态。当
放大器配置为非反相放大器，反馈（RF）和增益（RG）电阻网络形成
放大器输出的并联负载。为了保护放大器的输入级，
反相和非反相输入引脚之间的背对背保护二极管，如图48所示。当
如果放大器输入引脚之间的差分电压超过二极管电压降，则在输入之间产生额外的低阻抗路径。
+
±
GND
+
±
射频
穿越火线
OPA858
5伏
GND
3.4伏
100伏
20
OPA858
SBOS629A–2018年4月–2018年7月修订www.ti.com
产品文件夹链接：OPA858
提交文件反馈版权©2018，德克萨斯仪器公司
10.应用和实施
注
以下应用部分中的信息不属于TI组件
且TI不保证其准确性或完整性。TI的客户是：
负责确定组件的适用性。客户应
验证和测试其设计实现，以确认系统功能。
10.1申请信息
10.1.1使用OPA858作为跨阻抗放大器
OPA858的设计经过了优化，以满足行业对宽带、低噪声不断增长的需求
光电二极管放大器。跨阻抗放大器的闭环带宽是以下函数：
1.总输入电容。这包括光电二极管电容、放大器的输入电容
（共模和差分电容）以及来自PCB的任何杂散电容。
2.运算放大器增益带宽积（GBWP），
3.跨阻抗增益RF。
图56跨阻抗放大器电路
图56显示了配置为TIA的OPA858，其中雪崩光电二极管（APD）反向偏置，以便：
它的阴极连接到一个大的正偏压。在这种配置中，APD向运算放大器提供电流
使得输出相对于输入共模电压在负方向上摆动。到
OPA858共模被设置为接近正极限，
正极供电轨的电压为1.6 V。
反馈电阻RF和输入电容在噪声增益中形成一个零，如果留下会导致不稳定性
未经检查。为了抵消零的影响，通过将反馈电容器（CF.）添加到
噪声增益传递函数。高速放大器应用报告中的跨阻抗考虑
讨论说明如何补偿跨阻放大器特定增益的理论和方程
以及输入电容。应用程序报告中的带宽和补偿公式可在
Microsoft Excel™ 计算器关于跨阻抗放大器，您需要了解的内容–1部分提供了
链接到计算器。

ALCL-13-5 380-500V 用于系统高压变频器 

ALCL-13-5 380-500V 用于系统高压变频器 

Connecting the PD pin low disables the amplifier and places the output in a high-impedance state. When the
amplifier is configured as a noninverting amplifier, the feedback (RF) and gain (RG) resistor network form a
parallel load to the output of the amplifier. To protect the input stage of the amplifier, the OPA858 uses internal,
back-to-back protection diodes between the inverting and noninverting input pins as Figure 48 shows. When the
differential voltage between the input pins of the amplifier exceeds a diode voltage drop, an additional lowimpedance path is created between the inputs.
+
±
GND
+
±
RF
CF
OPA858
5 V
GND
3.4 V
100 V
20
OPA858
SBOS629A –APRIL 2018–REVISED JULY 2018 www.ti.com
Product Folder Links: OPA858
Submit Documentation Feedback Copyright © 2018, Texas Instruments Incorporated
10 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
10.1 Application Information
10.1.1 Using the OPA858 as a Transimpedance Amplifier
The OPA858 design has been optimized to meet the industry's growing demand for wideband, low-noise
photodiode amplifiers. The closed-loop bandwidth of a transimpedance amplifier is a function of the following:
1. The total input capacitance. This includes the photodiode capacitance, input capacitance of the amplifier
(common-mode and differential capacitance) and any stray capacitance from the PCB.
2. The op amp gain bandwidth product (GBWP), and,
3. The transimpedance gain RF.
Figure 56. Transimpedance Amplifier Circuit
Figure 56 shows the OPA858 configured as a TIA with the avalanche photodiode (APD) reverse biased such that
its cathode is tied to a large positive bias voltage. In this configuration the APD sources current into the op amp
feedback loop so that the output swings in a negative direction relative to the input common-mode voltage. To
maximize the output swing in the negative direction, the OPA858 common-mode is set close to the positive limit,
1.6 V from the positive supply rail.
The feedback resistance RF and the input capacitance form a zero in the noise gain that results in instability if left
unchecked. To counteract the effect of the zero, a pole is inserted by adding the feedback capacitor (CF.) into the
noise gain transfer function. The Transimpedance Considerations for High-Speed Amplifiers application report
discusses theories and equations that show how to compensate a transimpedance amplifier for a particular gain
and input capacitance. The bandwidth and compensation equations from the application report are available in a
Microsoft Excel ™ calculator. What You Need To Know About Transimpedance Amplifiers – Part 1 provides a
link to the calculator.