最近霍尔效应电流感应的趋势

最近霍尔效应电流感应的趋势

By John Cummings, Michael C. Doogue, Andreas P. Friedrich

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Abstract

本文介绍了基于集成霍尔效应的电流传感器IC的最新进展。它涵盖了用于将主要电流路径集成到系统中的各种包装概念，IC参数的主要改进，以及用于不间断电源（UPS），逆变器和电池监控的典型应用电路的一些示例。

Introduction

The demand for low-cost, accurate, small-size current sensor solutions has grown rapidly during the last decade, in industrial, automotive, commercial, and communications systems. Various technologies can be used to transduce an electric current to a proportional voltage. The advantages of a Hall-effect magnetic detector are the inherent voltage isolation from the current path and the integration of the Hall element and interface electronics on a single silicon chip.[1] New design concepts and the systematic use of advanced BiCMOS technology have allowed further improvements in IC performance. These also have opened the door to new product approaches by supporting the integration of additional functions, such as power protection, in the same current sensor IC. This paper covers the basic packaging and IC design concepts of the Allegro™ ACS current sensor IC family and explores some recent trends that have enabled Allegro to develop its next generation of fully integrated low-cost current sensor devices.

Packaging Concept

Allegro电流传感器IC器件的特点是整合整体线性霍尔IC和低电阻初级电流导通路径，以单次包覆成型包装。通过霍尔换能器相对于铜导体的近距离和精确定位进行优化器件精度。低功率损耗和高压隔离是包装概念的内在型。封装电流测量系统的最终尺寸，形状和附加部件取决于要测量的初级电流的幅度。本节详细介绍了针对不同电流测量范围的创新包装技术。

Currents up to 20 A

对于小的标称电流，高达±20a，霍尔模具和初级电流路径在标准尺寸SOIC8表面安装封装中封装，如图1所示，这提供了兼容的紧凑，低轮廓解决方案具有大容量自动化板组装技术。使用倒装芯片技术允许在霍尔元件的主动面和被被感测电流产生的磁场之间的优化磁耦合。因此不需要磁通集中器。用于电流检测的铜路径的内阻通常为1.5MΩ，用于低功率损耗。电源端子也与低电压信号I / O引脚电隔离。仔细的IC和封装设计允许进一步提高装置的电压隔离，典型的直流隔离电压为5 kV，并且在初级电流之间具有1.6kV最小和2.5kV的RMS隔离电压为1.6kV路径和信号侧。

Figure 1. Internal structure of an ACS package, showing the U-shaped primary copper conductor and the single flip-chip–mounted Hall IC.

Figure 2. Internal structure of the CB package, showing the primary conductor (copper, left), the flux concentrator (red) and the linear sip Hall ic (black) and signal pins (copper, right).

图3.±20 A（LC封装）和±200a（CB封装）电流传感器IC的照片，如硬币所示。

Currents up to 200 A

For higher currents, the cross section of the copper conductor has to be increased to accommodate the current density within the material, which is provided in the CB package. Because of the magnetic coupling between this thicker conductor and the linear Hall element, a flux concentrator has to be used. The copper path, linear SIP Hall device, and concentrator are precisely assembled before being overmolded. Through careful design of the system, the primary conductor resistance is typically as low as 100 µΩ and a minimum rms isolation voltage of 3 kV (at 60 Hz for 1 minute) is achieved between primary path and signal sides. Figure 2 shows the internal structure of such a ±200 A current sensor, and figure 3 shows a photograph of both this and the ±20 A package types.

200 a上方的电流

If currents to be measured are higher than 200 A, the ICs can be used in a current divider configuration.[2] This method involves splitting the path of the current being sensed. The simplest approach is to design a notched bus bar such that only a well-controlled fraction of the current flows through the device, the other going through a shunt path (see figure 4). The current split ratio is determined by the geometry of the bus bar. An inherent disadvantage of this approach is that it reduces the current resolution by the same proportion as the current is divided.

The resolution of the current sensing system can be increased if the current is split equally and two devices are used in parallel (see figure 5). A simple circuit involving level-shifting and adding the outputs of the two devices can be used to obtain a linear output proportional to the total primary current.[2]

图4.当前分频器配置。电流传感器IC可以直接连接到汇流条。

Figure 5. Equal current splitting with enhanced resolution. The outputs of the two devices can be combined to obtain a linear output proportional to the total current to be sensed.

IC Design

This section details the basic chip architecture and most important IC parameters.

框图该装置的中心元件是一种精确的低偏置硅霍尔IC。框图如图6所示。由初级电流产生的磁通量会影响霍尔元素。使用BICMOS斩波器稳定电路来减少信号偏移，并在其工作温度范围内稳定IC的输出。[3]片上电子器件产生与输入电流成比例的模拟电压。

Figure 6. Block diagram of the circuit.

The output is ratiometric, which means that both the offset and sensitivity scale with V_CC。设备精度优化到行尾trimming of the offset, sensitivity, and temperature response. The ICs are designed to measure both positive and negative currents, but the parameters can be trimmed for uni-directionality if required. The device is trimmed after packaging in order to reduce package stress effects on the Hall element. As shown in figure 6, an external bypass capacitor is recommended, to reduce noise. If the bandwidth of the application allows it, a simple rc filter can be used at the output to further improve signal-to-noise ratio.

±20 A Model Main Features虽然SOIC8器件设计为±20a，但它们可以承受高达100 A的大瞬态过度电流。确定器件的过电流能力的限制因素是IC的结温（T_J(max), which equals 165°C), and is therefore determined by the thermal design of the printed circuit board (PCB) in the application.

The main features and benefits are summarized as follows:

• AC and DC current measurement
• 1.5 mΩ internal conductor resistance
• 1600 VRMS (min) isolation voltage
• 4.5 to 5.5 V supply operation
• 50 kHz bandwidth
• 室温下的总输出误差±1.5％
• operating temperature range of –40°C to 85°C
• small footprint, low-profile SOIC8 package
• near-zero magnetic hysteresis
• 电源电压的比率输出
• RoHS compliant (flip-chip high-temperature Pb-based solder balls are currently exempt from RoHS)

±200 A模型主要功能The thickness of the copper conductor allows survival of the device at up to 5× overcurrent conditions. The main features and benefits are summarized as follows:

• AC and DC current measurement
• 100µΩ内部导体电阻
• 3000 VRMS (min) isolation voltage
• 4.5 to 5.5 V supply operation
• 35 to 50 kHz bandwidth
• ±1.0% total output error at room temperature
• operating temperature range –40°C to 150°C (a function of primary current)
• small package size, easy mounting capability
• 电源电压的比率输出
• lead (Pb) free

Recent Trends

Current-sensing solutions for advanced industrial, automotive, commercial, and communications systems are facing new challenges. Although the solutions presented in the previous paragraphs are already covering a large variety of customer requirements, the general trend is clearly towards low cost, high accuracy, and small size systems, but with added functionality. This section describes two innovative devices developed at Allegro to address these needs.

改进了IC表现In an effort to further improve the characteristics of the ±20 A low-profile SOIC8, Allegro developed a third generation device with specific focus on noise and total output error reduction. The chip design was developed on the latest Allegro low-noise 0.65 µm BiCMOS process (DABIC6). A total of 23 programming bits can be used to optimize following IC parameters after packaging:

• quiescent output voltage
• sensitivity
• 灵敏度温度系数

The combination of improved process performance, new design concepts, and additional programming capability resulted in a 2× reduction in noise. The total output error at I_P= ±20 A was improved from ±8.4% to ±1.5% in an industrial temperature range, 40°C to 85°C.

This new device also has a filter pin that can be used to set the –3 dB point with a capacitor. This reduces the number of external components required to improve IC resolution (no sense resistor needed). The peak-to-peak current noise levels, for different filter capacitor values, at T = –40°C to 85°C, and IP = ±20 A, are given in the following table:

This new ACS712 device is a drop-in replacement of the previous generations, ACS704 and ACS706.

Added Functionality

For large volume applications, it may be worth integrating some additional functions on the Hall IC that would usually be realized with external components. In the implementation described below, this approach resulted in a new protection IC with integrated hot-swap gate driver and internal Hall-effect based element.

The block diagram of this ACS760 device is shown in figure 7. The power supply load is measured without the use of an external sense resistor. The part uses an integrated 1.5 mΩ copper conductor and a Hall-effect element to accurately measure load currents up to 30 A. The device contains overcurrent protection circuitry that trips at a user-selectable level between 30 and 40 A. If an overcurrent condition is detected, the fault output of the part trips and the gate of the external mosfet is pulled to ground. The delay between the detection of an overcurrent condition and gate shutdown is set by an external capacitor.

图7.具有集成热插拔栅极驱动器和基于内部1.5Ω霍尔效应元素的保护IC的框图。

应用例子

本节提供了两个应用示例，其中ACS设备支持最佳雷竞技最新网址电流传感解决方案。

Battery MonitoringSmart battery systems require circuitry to monitor cell voltages, temperatures, and currents. For capacity monitoring applications, all of these measurements are critical. The most difficult to design-in properly, however, is current measurement. The reasons for this are the requirements for accuracy, power dissipation, and solution size.

Current measurement accuracy is essential to ensuring that the capacity monitoring algorithms are working well. The traditional method of measuring this current is with a shunt in the ground path or on the low side. The key problem with this method is that, to minimize I²R losses, the value of the shunt needs to remain very small. With this approach, low-current measurement accuracy becomes compromised. What it means for notebook computer applications is that during suspend, hibernate, or other low-power states, it is difficult for the battery to accurately monitor the current flowing into the system.

If the battery is using a 10 mΩ sense resistor to minimize power dissipation at nominal loads, when in a low-power state with only 50 mA of power draw, the voltage across the shunt would be only 500 pV. This voltage is very difficult to resolve, and complicated algorithms for estimating the residual capacity must be developed for the battery in order to compensate for this effect. These routines are conservative in nature, meaning that they tend to assume that the battery is losing a little more capacity than is actually calculated. The result can be an appearance of excessive loss in battery capacity over time.

Depending on the battery and the application, sense resistors in the range of 1 to 2 W would be required to monitor the currents. Typically in portable solutions, however, there is not enough space for 2 W resistors, so the solution is usually limited to 1 W resistors. For higher-current solutions, multiple resistors are used in parallel to keep the power ratings within the device limitations. Both solutions have a large impact on the board real estate required to fit these components.

By using a Hall-effect device as a shunt solution in the battery pack, the power dissipation in the pack can be reduced. The advantage of using Hall-effect devices is readily apparent with the low insertion loss of the device. In an SOIC8 package, the ACS712 lead-frame insertion loss is only 1.5 mΩ. The difference in power consumption over a range of load currents is shown in figure 8.

The use of a Hall-effect device as shown in figure 9 can increase the accuracy of current measurements. This block diagram shows a high current path and a low current path. The low-current path can be enabled for better accuracy at monitoring small currents. Not only does the solution shown in figure 9 provide higher accuracy for lower charge and discharge currents, but also it provides more signal than the shunt solution over the measurement range. Assuming that the Hall-effect device has a gain of 100 mV/A, this signal is much larger than the resulting signal across a shunt resistor, as shown below in figure 10.

Figure 8. Power loss in shunt versus Hall-effect current sensing solutions.

Figure 9. Improved accuracy and efficiency in battery monitoring with Hall-effect devices.

Figure 10. Output voltage of a Hall-effect solution compared to a 20 mΩ shunt.

The step increase in gain with the Hall-effect solution assumes that the application enables the high current path shown in figure 9. The actual threshold for the transition and level of hysteresis desired will be a function of the application as well as the value of the shunt employed.

The use of Hall-effect devices in battery systems will help to reduce the PCB area required for a shunt sensing solution and enable high-side sensing, which does not interrupt the ground path. The two major benefits in using a Hall-effect device are improving current measurement accuracy over a wider current range, and reducing power consumption by significantly reducing the 1²失去分流器。

Hall Effect Devices in UPS and Inverter ApplicationsThe use of either Hall-effect devices or current transformers (CT) is common in UPS systems. While CTs are seen as low-cost solutions, they actually require more support components than a Hall-effect solution and are strictly limited to ac applications. Another secondary cost attributed to using CTs to monitor the AC line voltage is the additional circuitry to manage the effects of inrush and possible core saturation during an inrush event.

UPS solutions require using the line voltage to charge a battery that is used to supply line voltage for a system in the event of a power failure. The goal of the UPS is to supply as much energy as possible with the maximum efficiency. For example, a 2200 VA UPS requires a typical 3-hour charge time. This same UPS can only supply approximately 24 minutes of power at half load (990 W) and 6.7 minutes at full load (1980 W). The input and output currents are monitored both for protection and to be able to show the battery state of charge with a level of confidence.

ACS712采用霍尔设备监控的理想选择ing the input power or battery charge current for several reasons. The obvious benefit for a small form-factor Hall-effect solution is that the volume required is a fraction of the equivalent CT solution, and in addition there is an elimination of gain and additional protection components. The reason for this is that the ACS712 cannot overshoot the voltage on the isolated side of the device.

当在高负载下为逆变器阶段供电时，具有霍尔效应IC的最佳位置是线电压本身，直接监测负载电流。原因是线电压电流可以高达15到20 a_RMS, whereas the battery sourcing current may be in excess of 50 to 60 A, depending on the voltage of the battery stack and the efficiency of the converter. Below, figure 11 shows an example of using a Hall-effect device in a ups power train.

Figure 11. UPS power train architecture.

This next generation of Hall-effect devices is helping to resolve known issues with CTs and to improve the reliability of systems. By using Hall-effect devices in the battery charging system and inverter power train, the efficiency of the converters can be optimized. This can help to reduce the overall size of the system and save costs.

Conclusion

创新工业电流传感解决方案l, automotive, commercial, and communications systems were presented. The packaged devices consist of a low-resistance primary current path and a monolithic linear Hall-effect IC that integrates the Hall element and state-of-the art BiCMOS interface circuitry.

该器件覆盖高达±200a的测量范围，并且还可以使用当前分频器配置设计成更高的电流应用。雷竞技最新网址详细介绍了具有添加功能的低成本，高精度和小型电流测量系统的新方法，并提供了两个应用示例。

Notes

1. R.S. Popovic, "Hall Effect Devices", 2nd ed., IoP Publishing Ltd., 2004.
2. R. Dickinson and A. P. Friedrich, Using Allegro Current Sensors in Current Divider Configurations for Extended Measurement Range, Allegro MicroSystems, LLC , applications note AN295036, April 2005.
3. A. Bilotti, G. Monreal and R. Vig, "Monolithic Magnetic Hall Sensor Using Dynamic Quadrature Offset Cancellation," IEEE J. Solid-State Circuits 32, no. 6 (1997): 829-36.