A Micro-Packaged Linear Current Sensor IC

Primary conductor resistance of only 0.6 mΩ reduces power dissipation

由Shaun Milano.
雷竞技竞猜下载Allegro Microsystems，LLC

线性电流传感器IC，ACS711.，安装在0.75毫米厚的低轮廓封装中，仅测量3毫米×3毫米！它设计用于低侧，小于100 V检测应用，需要5 A至30个连续电流检测。雷竞技最新网址

传统上，电流传感已经通过感测电阻或电流互感器来完成，可以占用大型PCB区域。感测电阻值10到50mΩ可以在更高电流下燃烧大量功率，从而降低了整体系统效率，而电流变压器消耗大型PCB房地产。霍尔效应传感器IC用于提供导体中电流的非接触方法，并提供与导体中流动的电流成比例的电压信号。

来自Allegro™Microsystems，LLC的新型电流传感器IC，ACS711（图1和2）用真正的小，3毫米占3mm的占地面积，只有0.6mΩ导体电阻，可通过0.6mΩ的电阻来解决尺寸问题，从而降低了按顺序的功耗典型检测电阻OP-AMP解决方案的幅度。电流传感器IC的完全集成允许在Allegro的工厂编程提供更准确的解决方案，同时通过降低电流承载导体中的功率损耗来提供小尺寸和更高效率的额外优势。

图1.与美国的相比，ACS711 QFN封装尺寸
10-cent coin

图2. ACS711具有QFN结构的设备：黄色是IC
chip, red is the Hall element, green lines represent magnetic flux,
and blue is the sensed current path

包装

Hall current sensor ICs with one turn and no magnetic core do not produce a large magnetic field, so placing the Hall sensing-element in close proximity to the sensed current is an attractive approach. The flux surrounding a conductor may be only a hundred gauss (10 mT) or less, and this diminishes rapidly with the distance of the Hall element from the conductor.

为了优化性能，ACS711器件采用Allegro专利的倒装芯片磁场传感技术，如图2所示。倒装芯片使用允许IC的霍尔换能器部分的有效区域（如图2所示。）在硅的表面上被放置在最接近的初级导体上。这允许出色的信号耦合。

Classic flip-chip technology is employed, which makes the necessary connections to the signal circuit and supports the chip above the current conductor on the leadframe. The primary current path is efficiently channeled to the Hall element via a patented exposed current loop design, with terminations soldered directly to the PCB traces. With such close magnetic coupling to the conductor, signal sensitivity is maximized and the device can produce 90 mV/A and 45 mV/A for sensing 15 A and 31 A full-scale current, and the sensor IC requires only a 3.3 V supply.

Flip-chip technology also allows case molding plastic to fill the small spaces between the primary current carrying conductor and both the die surface and the device signal leads, providing galvanic (voltage) isolation. With the attractive small dimensions of this device, the package provides isolation only to supply voltage values below mains line voltage. The ACS711 has been optimized for low voltage circuits, < 100 V, such as: 48 V solar circuits, communications, and consumer electronics and audio applications. The device is also economical to assemble into finished products and is excellent for low-side sensing applications in residential and commercial white goods appliances and with general-use motor drivers.

尽管它体积小,遗传代数ACS711可以感知ively large currents in the QFN package, up to ±31 A. Sense resistor power dissipation is significant at higher current ranges and conducting such current levels in and out of IC packages has been a traditional limitation. The QFN package solves this issue with two large solder pads on the mounting surface and with careful detail to the shape of the primary sensed current conducting loop. The design uses substantial copper conductors within the package to form the sensed current loop, without bond wires. The primary conductor resistance in the QFN is only 0.6 mΩ, an order of magnitude less than most sense resistors employed in low-side sensing configurations. This reduces power consumption, and typical power dissipation at 30 A is only 0.54 W and at 15 A is just 0.135 W. This not only makes a contribution to system efficiency, but also allows the device to stay cool even at elevated currents. If customers prefer a leaded package for certain applications, a companion package, the SOIC-8, is also available for the ACS711 product. Please refer to the Allegro website at www.wasanxing.com for more linear current sensing ranges available.

焊接和热特性

Notwithstanding the low power dissipation, an even lower thermal resistance to ambient than that inherently provided by the relatively small, 3 mm²QFN package is required. Wide, highcurrent copper traces on the printed circuit board (PCB) are adequate to help cool the device, if designed properly. An example is shown in figure 3, the layout on the ACS711 prototyping board available from Allegro. Note that the two large pad areas, 4.5 mm across, are only slightly larger than the very small QFN package outline. On this board, two layers of 4 oz. copper are used, linked by thermal vias (those under the QFN can be filled or eliminated if necessary) to enhance thermal performance. The vias under the QFN can be filled or eliminated if necessary, as some customers find this difficult to accomplish in a production environment. Further design details and guidance for PCB mounting are available from Allegro.

图3.

图3. QFN电流传感器IC的PCB布局（Allegro Prototyping
board 85-0528)

Using the Allegro PCB of figure 3, temperature measurements were made across a range of sensed current levels. Figure 4 shows the results. The graph shows that at an ambient temperature of 85°C the sensor IC package can withstand 45 A continuous current before reaching the maximum recommended junction (die) temperature, 165°C. With proper PCB design, the device can be safely used in 30 A continuous-current applications at 85°C ambient temperature, with an approximately 50°C margin of safety before reaching a die temperature of 165°C.

图4.

图4。QFN的热力性能mounted on the PCB

器件功能，故障输出和准确性

The voltage signal is dependent on the direction of the current flow, enabling measurement of bi-directional current flow, both AC and DC. At a zero-current level, the output voltage signal is half the supply voltage.

The ACS711 sensor IC also integrates a factory-programmed fast response digital fault output that has a 1.3 μs response time. It is set at 100% of the maximum current rating of the sensor IC. This fast fault signal can be used to prevent the destruction of IGBTs or other switching devices during short circuit or overcurrent conditions, or as a redundant fault feature in motor control applications.

Another inherent disadvantage of sense resistor with op-amp solutions is a reduction in accuracy with changes in temperature, because the sense resistor value changes. Hall-based sensor ICs are not subject to this error because the magnetic field generated by current flowing in a conductor is not temperature dependent. The Allegro ACS711 provides additional protection, against package thermal stress, through the application of an advanced Bi-CMOS process with built-in chopper circuitry to compensate for Hall element offset voltage changes. The fully integrated architecture of the ACS711 sensor IC further allows adjustment programming at Allegro end-of-line production testing to further reduce errors in gain and offset, delivering a more accurate sensing solution.

Summary

高级Allegro专利倒装芯片封装用于线性Hall ICS允许创建微型3毫米×3毫米完全集成的电流传感器装置，Allegro Microsystems ACS711，其内部电阻仅为0.6mΩ的内部电阻，在包装中产生雷竞技竞猜下载真的可以吸收热量。与适当的PCB设计一起使用，该设备可用于具有超过30个连续电流的应用，同时与现有的检测电阻解决方案相比将功耗降低了幅度。雷竞技最新网址

Factory programming provides high accuracy in this IC, with an integrated fast response fault output. Together these techniques deliver the smallest current sensing footprint available for your application without compromising accuracy.

图5.

图5. ACS711的典型应用电路

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.