Differential Current Sensing with the 1 MHz Bandwidth ACS733
Differential Current Sensing with the 1 MHz Bandwidth ACS733
作者：Maxwell McNally，A亚博棋牌游戏llegro MicroSystems，LLC
摘要
本应用说明描述了新的高度隔离、高带宽的使用ACS733霍尔效应电流传感器集成电路（IC）的Allegro微系统，并给出了一个概述其特点和优势，比高速电流互感器（CT）亚博棋牌游戏电流传感解决方案。
介绍
TheACS733是第一个1兆赫带宽霍尔效应电流传感器芯片3600伏有效值isolation from Allegro. The sensor provides users with an accurate, low cost solution for isolated current sensing at high bandwidths with a small form factor. The device’s high bandwidth is accomplished by a high-speed analog signal path that employs differential sensing to provide immunity to interfering common mode magnetic fields. Figure 1 below shows the pinout of the device. The IC is packaged in the wide body SOIC 16 pin LA package. Pins 1 through 8 of the part are reserved for current input, four pins for both the positive and negative terminals. These pins are all internally connected with low resistance leadframe copper for better thermal performance.
传感器的针脚9到16ACS733是输出信号引脚。VCC和GND用于为设备供电，VIOUT是一个模拟输出，表示IP总线上感应到的电流电平。这个断层当检测到少量电流时，引脚为高电平，但如果检测到高于某个阈值的电流，引脚将被拉低。该电平在VOC引脚上设置，分压电平为VCC的百分比，对应于设备最大额定电流的百分比。程序引脚用于工厂校准，应与地面连接，以在应用中获得最佳ESD性能。
Differential Sensing
依靠磁场进行测量的电流传感技术可能会受到外部磁场的影响。通过使用两个霍尔板测量由输入电流产生的场的相反极性，ACS733能够抑制共模场。这使得te部件可以在其他电流迹线附近使用。ACS733具有约-40 dB的共模场抑制，适用于均匀恒定的场。有关差分感应的更多信息，请参阅应用说明“无铁心霍尔效应电流传感器集成电路中的共模场抑制”.
The common-mode field rejection of the ACS733 is an advantage over a CT, because a CT core can saturate in the presence of external magnetic field and change the operating characteristics of the device.
噪声和灵敏度
The ACS733 has a typical noise density of 80 μA/√Hz. Across the entire bandwidth of 1 MHz, this becomes an input-referred total noise of 100 mARMS. At different sensitivities, this amperage error will manifest at the output as different levels of mV error, but this indicates the part has an effective 100 mA resolution. Table 1 below compares the mV output error seen for the currently offered sensitivities of the ACS733. However, this noise can be reduced by decreasing the effective bandwidth of the device, either with oversampling and averaging, or by filtering the output with an RC filter.
表1：灵敏度和产生的mV噪声
| Part | 敏感 （毫伏/年） |
噪声密度 (μA/√Hz) |
分辨率 (mA) |
错误 (mV) |
| 733-20AB | 66 | 80 | 100 | 6.6 |
| 733-40AU | 4.4 | |||
| 733-40AB | 33 | 3.3 | ||
| 733-65AB | 20 | 2 |
高带宽操作和快速响应时间
The ACS733 has a high operating bandwidth of 1 MHz. The device’s high speed analog signal path provides the fastest response time of any Allegro fully integrated current sensor IC. The typical response time to a step input is <800 ns on the output, and the typical fault output responds in <600 ns. Figure 3 shows the ACS733 responding to a current step compared to the response of a typical current transformer (CT). Both respond very quickly to the 1 μs input step.
User-Settable Overcurrent Fault Detection
的一个附加功能ACS733is the user-settable overcurrent open-drain NMOS fault output. This allows an even faster reporting of overcurrent or shorting events. This pin will detect overcurrent events faster than ADC conversion of the analog output signal. The fault level of the ACS733 can be set to any level from 50% of the maximum primary sensing current (IPR（最大值）)，一直到我的200%PR（最大值）在VOC引脚上使用简单的电阻分压器。这为客户提供了一种为其特定应用设置过电流水平的简单方法。
VOC引脚上的电阻分压器设置为VCC的10%，以将故障级别设置为I的50%公关(最大), and a voltage level of 40% of VCC to set the fault level at 200% of IPR（最大值）. Table 2 below shows these calculations for the ACS733 at four different fault levels. Equation 1 shows the calculation for the percent of VCC for any desired fault level.
VOCPercent=故障Percent× 0.2 (1)
Table 2: Fault Level and Voltage Divider Examples
| 供应 Voltage (V) |
VOC (%VCC) |
VOC (V) |
Fault Level （%IPR（最大值）） |
Resistors (kΩ) |
| 3.3 |
10 | 0.33 | 50 | 9/1 |
| 20 | 0.66 | 100 | 8/2 | |
| 30 | 0.99 | 150 | 7 / 3 | |
| 40 | 1.32 | 200 | 6 / 4 |
未检测到故障时，故障信号高。当发生过电流事件时，开漏NMOS输出会拉取断层引脚低。下面的图4显示了故障输出响应于电流阶跃输入的功能。由于该设备有一个开漏NMOS输出，他们可以逻辑或'的多相系统，以一个单一的故障中断数字I/O引脚的控制器。
Compact Form Factor
A current transformer is bulky, requiring an offset core with windings and a resistive load to sense current. The ACS733 is a fully integrated sensing solution in a standard SOIC16W surface mount package that takes up minimal printed circuit board (PCB) area. Below, Figure 5 shows the size of the ACS733 compared to two CTs. When trying to minimize the size of a system, the ability to run the current trace on the board to the part which is mounted to the PCB would offer a significant space-saving advantage.
High Voltage Isolation
尽管其体积小，专利封装技术提供了高电压隔离。高电流引脚与低电压信号引脚隔离，因为只需要感应磁场。SOIC16W（LA封装）中的ACS733已根据UL 60950-1（第2版）认证为3600 VRMS。
结论
TheACS733具有一系列特性，在需要高速和高电压隔离电流传感时具有显著优势。lasoicw封装是一种表面贴装解决方案，与体积庞大的电流互感器解决方案相比，它易于集成并减少PCB面积。ACS733的SOIC16宽体封装提供3600 VRMS与信号引脚的载流迹线隔离。传感器IC在Allegro工厂的工作温度范围内进行了优化，并在发生过电流和短路事件时提供开漏NMOS故障输出，以实现快速数字输出。这种完全集成的传感技术是真正的片上系统解决方案，与汽车和工业应用兼容，使工程师能够轻松地将设计融入其应用中。亚博尊贵会员