Achieving Closed-Loop Accuracy in Open-Loop Current Sensors
Achieving Closed-Loop Accuracy in Open-Loop Current Sensors
By Shaun Milano,
Allegro MicroSystems, LLC
关闭d-loop current sensing technology is employed in many industrial and automotive applications for accurate current sensing. By employing proprietary packaging techniques and advanced integrated algorithms in a single monolithic, fully integrated current sensor IC, Allegro MicroSystems, LLC has developed magnetic-based current sensor IC solutions that achieve near closed-loop accuracy using an open-loop topology. The packaging methods and algorithms used to achieve this are the topic of this paper and will be discussed in detail.
Open Loop vs. Closed Loop Current Sensing Topology
一般来说,一个开环采用霍尔传感器使用s a magnetic transducer to create a voltage that is proportional to the current being sensed. This signal is then amplified to provide an analog output signal proportional to the current flowing in the conductor. The conductor is fed through the center of a ferromagnetic core to concentrate the field and the magnetic transducer is placed in the gap of the core. This topology is shown in Figure 1. In an open-loop configuration, any non-linearity or drift in the sensitivity of the Hall-effect current sensor IC over temperature can produce error. A closed-loop sensor uses a coil that is actively driven by the current sensor IC to produce a magnetic field that opposes the field produced by the current in the conductor.
The Hall sensor then observes a net zero magnetic field at the transducer. The output is generated by a resistor that has a voltage proportional to the current being driven into the coil, which is also proportional to the current flowing in the primary conductor leveraged by the number of turns of the coil wound around the magnetic core. The closed-loop topology is shown in Figure 2. Closed-loop current sensors not only require ferromagnetic cores but also a coil and additional higher power amplifiers to drive the coil. While closed-loop current sensors are more complex than an openloop
配置，它们确实消除了与霍尔传感器IC相关的灵敏度误差，因为系统在零场的单点运行。闭环和开环霍尔效应电流传感器通常具有相同的零放大器输出电压性能，如果设计得当，因此开放和闭环传感器零放大器检测精度非常相似。闭环传感器的尺寸较大，比开环解决方案占用更多PCB区域。它们还可以消耗更多的电源，因为它们需要驾驶补偿线圈并且更昂贵，因为
附加线圈和线圈驱动电路。
开环与闭环感测的选择随后是所需的准确性和响应时间之一。如果应亚博尊贵会员用程序需要高精度，则闭环电流传感器通常是一种简单且明显的选择，因为它消除了系统中上述的敏感性非线性误差。闭环的快速响应时间是保护半导体开关，如用于控制应用中电流流量的IGBT和MOSFET。然后，挑战变成开环传感器，具有足够的精度和速度，即它成为这些应用程序的选项。亚博尊贵会员Allegroo开发了该技术，提供了一种开环解决方案，具有行业领先的小型尺寸，高精度和速度，比闭环解决方案的较低价格点低于闭环解决方案，使其成为新的逻辑选择。
开环传感器IC包装
Allegro current sensor ICs are unique in that most are fully integrated. Patented flip-chip packaging techniques are employed to create sufficient field to remove the need for a ferromagnetic
core. Figure 3 shows an SOIC16 current sensor IC configuration. Notice the current comes in and out of one side of the package and the signal leads are on the other side of the package. The
current generates a magnetic field that is focused at the center of the ¾ turn conductor seen in the top view of Figure 4. The IC is bumped, and a flip-chip assembly technique is employed to place
the magnetic Hall transducer over the area of maximum field.
The cross section view of Figure 4 also shows that there is no physical contact between the semiconductor IC and the current carrying conductor. This provides the galvanic isolation required
在许多高压应用中。亚博尊贵会员不同的封装占用脚印将提供不同的隔离级别，如常见的UL和TUV规范UL / TUV60950-1版本
2. See device datasheets at//www.wangzuanquan.com/en/Products/Current-Sensor-ICs.aspxfor isolation ratings of individual sensors. The conductor resistance of these surface mount packages is very low at only 1 mΩ. These packages can be used for continuous currents up to 50 A RMS or DC with nominal thermal considerations on the customer PCB. A detailed application note on package thermal performance for DC and transient currents is located at the following link.//www.wangzuanquan.com/en/design-center/technical-documents/hall-yseSensor-publentications/dc-and-transient-current-capability-fuse-characteristics.aspx.
先进的半导体算法，提高精度和速度
The AllegroACS720 current sensor ICprovides an excellent example of the new open-loop technology. Figure 5 shows a typical block diagram of the IC.
The Allegro BiCMOS mixed signal semiconductor process allows for low offset analog circuitry together with medium density digital circuitry, making it possible to integrate advanced algorithms onto a single monolithic integrated circuit. The analog signal path is designed to operate at 120 kHz bandwidth with a < 4 μs response time that works well in most motor control and green energy applications. For applications that require faster response times for protection against overcurrent faults, the ACS720 also has both a digital slow fault for overcurrent detection and a very fast digital fault current output for short circuit protection. The trip points for both fault outputs are user-configurable with a resistor divider on the VOC pins. The fast fault trips go active low in just over 1 μs and provide a signal that can be used to protect the semiconductor switches from shorting events. This provides the high speed protection needed for most applications.
该传感器还集成了针对逆变器应用优化的功能，其中功率和信号板通常由不同的电源电压供电。亚博尊贵会员ACS720内部调节器
在5 V电源上操作，具有大的电源抑制比，可为电源导轨上的噪声提供免疫力。然而，设备的输出是非避险和兼容的
使用3.3 V供应，可以直接进入信号板上的微处理器ADC。这允许输出信号偏移和灵敏度保持稳定，即使在5 V电源上的干扰也兼容3.3V。故障引脚也是打开NMOS器件，并且在多相逆变器中使用多个ACS720器件时，可以在逻辑上或在单个数字I / O引脚上一起。
为了优化温度的精度，IC具有集成的分段线性温度补偿算法，用于主信号路径增益和偏移。
Temperature Compensation Algorithm
通过添加包括EEPROM技术的数字温度补偿算法，大大提高了Allegro开环电流传感器IC的精度。分段线性
五边界之间的温度补偿s employed to drastically reduce the native drift of the analog signal path without sacrificing the signal bandwidth. Figure 6 illustrates the
technique. Both the zero amp output voltage (QVO) and sensitivity can be adjusted with the algorithm. The native drift of either QVO or sensitivity is illustrated by the dotted line, the dashed
线显示在边界之间添加的线性补偿，并且实线显示了传感器输出的产生行为。在图5中通知数字补偿
与主信号路径并行发生。这允许模拟输出保持高速，而增益和偏移被补偿随着温度随时间缓慢变化而补偿。
补偿参数在Allegro工厂的线路终端测试中编程，并通过集成EEPROM，温度传感器和数字分段线性来完成
temperature compensation algorithm on the IC. This end-of-line programming provides a stable zero amp output voltage and sensitivity over the entire operating temperature range.
Sensor Performance
The results of the patented packaging techniques and the integrated digital compensation algorithm provide a sensor with near ±1% accuracy over the entire temperature range and operating
bandwidth of the sensor. These results can be seen in the graphs in Figure 7 below. The QVO (offset) error is less than ±8 mV (±0.5%) over the entire operating temperature range, and the
sensitivity is only ±1% over temperature.
Summary
By combining unique packaging techniques and advanced mixed signal semiconductor processes with advanced digital temperature compensation algorithms, an open-loop current sensor IC
achieves closed-loop accuracy. The small PCB footprint and the elimination of bulky and expensive ferromagnetic cores make these current sensor ICs from Allegro easy to integrate into applications needing high accuracy and speed, all at a price point below a closed-loop sensing solution.
For more information on current sensor ICs, including layout recommendations and other application notes, see the Hall-Effect Sensor IC Publications landing page://www.wangzuanquan.com/en/design-center/technical-documents/hall-affect-sensor-publications.aspx.
附加申请说明，常见问题提出的问题和产品信息也可以在www.wangzuanquan.com上的Allegro网站上找到。
Applicable Patents
1. Gagnon et al., “Current Sensor”, US Patent 7,166,807; filed June 3, 2005, and issued January 23, 2007; Assignee: Allegro MicroSystems, LLC.
2. Doogue et al., “Current Sensor”, US Patent 7,709,754; filed August 26, 2003, and issued May 4, 2010; Assignee: Allegro MicroSystems, LLC.
3. Milano et al., “Reinforced isolation for current sensor with magnetic field transducer”, US Patent 8,907,437; filed July 22, 2011, and issued December 9, 2014; Assignee: Allegro MicroSystems, LLC.
Originally published in EE Times China, April 2018. Reprinted with permission.
Copyright ©2018, Allegro MicroSystems, LLC
The information contained in this document does not constitute any representation, warranty, assurance, guaranty, or inducement by Allegro to the customer with respect to the subject matter of this document. The information being provided does not guarantee that a process based on this information will be reliable, or that Allegro has explored all of the possible failure modes. It is the customer’s responsibility to do sufficient qualification testing of the final product to insure that it is reliable and meets all design requirements.