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在开环电流传感器中实现闭环精度

由Shaun Milano，
亚博棋牌游戏Allegro Microsystems，LLC

用于许多工业和汽车应用中采用闭环电流检测技术，用于精确电流检测。亚博尊贵会员通过使用专有的包装技术和在单一单体的全集成电流传感器IC中的专有包装技术和先进的集成算法，LLC开发了磁性电流传感器IC解决方案，使用开环拓扑实现近闭环精度。亚博棋牌游戏用于实现这一点的包装方法和算法是本文的主题，将详细讨论。

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
configuration, they do eliminate the sensitivity error associated with the Hall sensor IC, since the system is being operated at just a single point at zero field. Closed-loop and open-loop Hall-effect current sensors generally have the same zero amp output voltage performance if designed properly, and so open- and closed-loop sensor zero amp detection accuracy are very similar. Closed-loop sensors are larger in size and take up more PCB area than open-loop solutions. They also consume more power as they need to drive the compensation coil and are more expensive because
of the additional coil and coil drive circuitry.

The choice of open-loop versus closed-loop sensing then becomes one of accuracy and response time required. If applications demand high accuracy, a closed-loop current sensor is often an easy and obvious choice as it removes the aforementioned sensitivity nonlinearity error in the system. The fast response time of closed-loop is required to protect semiconductor switches, like IGBTs and MOSFETs that are used to control current flow in the application. The challenge then becomes making an open-loop sensor with sufficient accuracy and speed that it becomes an option for these applications. Allegro has developed the technology to provide an open-loop solution with industry-leading small form factor, high accuracy, and speed that draw less current than closed-loop solutions at a lower price point, making them the new logical choice.

Open-Loop Sensor IC Packaging

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
磁厅传感器在最大领域的区域。

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
在许多高电压应用。亚博尊贵会员不同package footprints will provide different levels of isolation as rated by a common and difficult UL and TUV specification UL/TUV60950-1 edition
2. See device datasheets at//www.wangzuanquan.com/en/products/current-sensor-ics.aspx.for 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-Effect-Sensor-IC-Publications/DC-and-Transient-Current-Capability-Fuse-Characteristics.aspx

**Figure 4: Top View and Cross Section**

Advanced Semiconductor Algorithms to Enhance Accuracy and Speed

The AllegroACS720电流传感器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.

The sensor also integrates features that are optimized for inverter applications where the power and signal boards are often powered by different supply voltages. The ACS720 internal regulator
operates on the 5 V power supply and has a large power supply rejection ratio that provides immunity to noise on the power rail. The output of the device however is nonratiometric and compatible
with 3.3 V supplies and can be fed directly in to the ADC of a microprocessor on the signal board. This allows the output signal offset and sensitivity to remain stable and 3.3 V compatible even with disturbances on the 5 V power supply. The fault pins are also open NMOS devices and can be logically OR’d together on a single digital I/O pin when using several ACS720 devices in multiphase inverters.

To optimize the accuracy over temperature, the IC has an integrated piecewise linear temperature compensation algorithm for both the main signal path gain and offset.

温度补偿算法

The accuracy of Allegro open-loop current sensor ICs is greatly enhanced with the addition of a digital temperature compensation algorithm that includes EEPROM technology. Piecewise linear
使用五个边界之间的温度补偿来大大减小模拟信号路径的天然漂移，而不会牺牲信号带宽。图6说明了
技术。零放大器输出电压（QVO）和灵敏度都可以用算法调整。虚线示出了QVO或灵敏度的本机漂移，虚线示出了虚线
line shows the linear compensation that is added between the boundaries, and the solid line shows the resulting behavior of the sensor output. Notice in Figure 5 that the digital compensation
happens in parallel with the main signal path. This allows the analog output to remain at high speed while the gain and offset are compensated as the temperature changes slowly over time.

The compensation parameters are programmed at the Allegro factory end-of-line testing and are accomplished by integrating an EEPROM, a temperature sensor, and the digital piecewise linear
IC上的温度补偿算法。该行终端编程在整个工作温度范围内提供稳定的零放大器输出电压和灵敏度。

传感器性能

获得专利的包装技术和集成数字补偿算法的结果提供了一个传感器，在整个温度范围内具有接近±1％的精度近±1％
传感器的带宽。这些结果可以在下面图7中的图表中看到。在整个工作温度范围内，QVO（偏移）误差小于±8 mV（±0.5％），以及
灵敏度在温度下仅±1％。

**Figure 7: Offset and Gain Error vs. Temperature: ±3 Sigma Data**

概括

通过使用先进的数字温度补偿算法结合独特的包装技术和先进的混合信号半导体工艺，开环电流传感器IC
实现闭环精度。小型PCB占地面积和庞大且昂贵的铁磁核心的消除使这些电流传感器IC从Allegro易于集成到需要高精度和速度的应用中，所有这些都以闭环传感解决方案低于价格点。亚博尊贵会员

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-Effect-Sensor-IC-Publications.aspx

Additional application notes, frequently asked questions, and product information can also be found on the Allegro website at www.wangzuanquan.com.

适用的专利
1. Gagnon等人，“电流传感器”，美国专利7,166,807;2005年6月3日提交，2007年1月23日发布;受让人：Allegr亚博棋牌游戏o MicroSystems，LLC。
2.摩托车等，“电流传感器”，美国专利7,709,754;2003年8月26日提交，并于2010年5月4日发布;受让人：Allegr亚博棋牌游戏o MicroSystems，LLC。
3. Milano等人，“带磁场传感器的电流传感器的增强隔离”，美国专利8,907,437;2011年7月22日提交，并发布2014年12月9日;受让人：Allegr亚博棋牌游戏o MicroSystems，LLC。

最初在2018年4月的EE Cimes刊登。转载许可。