E-00000-411-600-1 DCS过冷裕量计算器组件

E-00000-411-600-1 DCS过冷裕量计算器组件 

OPA858可与单个正电源（接地负电源）一起使用，无需改变
如果输入共模和输出摆幅在设备的线性操作中偏置，则性能。到
将电路从分体式电源更改为单电源配置，将所有电压电平移动一半
电源导轨之间的差异。在这种情况下，热垫必须接地。
9.4.2断电模式
OPA858具有断电模式，以减少静态电流以节省功率。图23和
图24显示了当PD引脚在禁用和启用之间切换时，OPA858的瞬态响应
美国。
PD禁用和启用阈值电压参考负电源。如果放大器是
配置3.3 V的正电源和接地的负电源，然后禁用和启用
阈值电压分别为0.65V和1.8V。如果放大器配置有±1.65 V电源，则
禁用和启用阈值电压分别为-1 V和0.15 V。如果放大器配置为：
±2.5-V电源，则阈值电压为-1.85 V和-0.7 V。
图54显示了当PD引脚从启用状态向下扫描时，典型放大器的开关行为
变为禁用状态。类似地，图55显示了典型放大器的开关行为，如PD引脚所示
从禁用状态向上扫描到启用状态。之间切换阈值的微小差异
下扫和上扫是由于放大器中设计的滞后，以增加其抗干扰性
PD引脚上的噪声。
图54.开关阈值（PD引脚从高电平扫描
低）
图55.开关阈值（PD引脚从低扫描
高）
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。
SBOS629A–2018年4月–2018年7月修订www.ti.com
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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R

E-00000-411-600-1 DCS过冷裕量计算器组件 

E-00000-411-600-1 DCS过冷裕量计算器组件 

The OPA858 can be used with a single positive supply (negative supply at ground) with no change in
performance if the input common-mode and output swing are biased within the linear operation of the device. To
change the circuit from a split-supply to a single-supply configuration, level shift all the voltages by half the
difference between the power supply rails. In this case, the thermal pad must be connected to ground.
9.4.2 Power-Down Mode
The OPA858 features a power-down mode to reduce the quiescent current to conserve power. Figure 23 and
Figure 24 show the transient response of the OPA858 as the PD pin toggles between the disabled and enabled
states.
The PD disable and enable threshold voltages are with reference to the negative supply. If the amplifier is
configured with the positive supply at 3.3 V and the negative supply at ground, then the disable and enable
threshold voltages are 0.65 V and 1.8 V, respectively. If the amplifier is configured with ±1.65-V supplies, then
the disable and enable threshold voltages are at –1 V and 0.15 V, respectively. If the amplifier is configured with
±2.5-V supplies, then the threshold voltages are at –1.85 V and –0.7 V.
Figure 54 shows the switching behavior of a typical amplifier as the PD pin is swept down from the enabled state
to the disabled state. Similarly Figure 55 shows the switching behavior of a typical amplifier as the PD pin is
swept up from the disabled state to the enabled state. The small difference in the switching thresholds between
the down sweep and the up sweep is due to the hysteresis designed into the amplifier to increase its immunity to
noise on the PD pin.
Figure 54. Switching Threshold (PD Pin Swept from HIGH
to LOW)
Figure 55. Switching Threshold (PD Pin Swept from LOW
to HIGH)
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.
SBOS629A –APRIL 2018–REVISED JULY 2018 www.ti.com
Product Folder Links: OPA858
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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 R