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单极霍尔效应传感器IC基础知识

单极霍尔效应传感器IC基础知识

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提供四种一般的霍尔效应IC设备，提供数字输出：单极开关，双极开关，全峰开关和锁存器。在本申请中描述了单极开关。类似的应用笔记双极交换机,全极开关， 和latchesare provided on the Allegro website.

单极霍尔效应传感器IC，通常被正磁场操作为“单极开关”。呈现足够强度（磁通密度）的南极（正）磁场的单个磁体将导致装置切换到其上的状态。打开后，单极IC将保持接通，直到磁场被移除，并且IC恢复到其关闭状态。

用于检测车辆换档杆的位置的应用如图1所示。换档杆包括磁铁（红色和蓝色圆筒）。微型黑匣子线是一系列单极开关设备。当车辆操作员移动杠杆时，磁铁通过各个霍尔设备移动。磁铁附近的器件经受磁场，并导通，但更多的远程设备不受影响并保持关闭。请注意，磁铁（彩色红色）的南极是朝向霍尔设备，并且霍尔设备以设备的品牌面向朝向磁体南极而定向。

Figure 1

图1.使用单极开关传感器IC的应用程序。超小型霍尔ICS切换器作为磁铁（红色和蓝色圆筒）在换档期间通过它们移动。

磁性开关点术语

以下是用于定义过渡点的术语，或者switchpoints, of Hall switch operation:

Figure 2

Figure 2. The Hall effect refers to the measurable voltage present when an applied current is influenced by a perpendicular magnetic field.

  • B.- 用于磁通密度的符号，用于确定HALL器件开关点的磁场的属性。在高斯（g）或tesla（t）中测量。转换为1g = 0.1 mt。

    B可以具有北极或南极极性，因此请记住代数惯例是有用的，由此B被指示为北极磁场的负值，以及作为南极性磁场的正值。本公约允许北方和南极度值的算术比较，其中该字段的相对强度由B的绝对值表示，并且标志表示该字段的极性。例如，A - 100克（北）场和100克（南）场具有等效强度，但极性相反。以同样的方式，a - 100g字段比a-50 g字段强。

  • B.op.- 磁功工作点;霍尔设备接通的强化磁场的水平。所得到的设备输出状态取决于各个设备电子设计。
  • B.RP− Magnetic release point; the level of a weakening magnetic field at which a Hall device switches off (or for some types of Hall devices, the level of a strengthening negative field given a positive Bop.）。所得到的设备输出状态取决于各个设备电子设计。
  • B.HYS.- 磁开关点滞后。霍尔设备的传递函数在开关点之间的偏移设计，以在磁场中过滤出小的波动，该磁场可能是应用中的机械振动或电磁噪声。B.HYS.= | Bop.- B.RP|。

典型的操作

当单极开关打开时，取决于器件IC输出级的设计，所产生的输出信号可以是逻辑高或逻辑低电平。图3显示了单极开关的可能输出状态。顶面板表示设计为输出逻辑低的开关（在输出晶体管饱和电压，V出去（坐了）通常在强南极地场中的<200 mV）。底部面板表示开关，该开关设计为输出逻辑高（直至全电源电压，VCC) under the same conditions.

Figure 3

图3.单极开关输出特性。顶部面板在存在强大的南极性场时显示切换到逻辑低电平，底板显示到逻辑高，也在南极性场中切换。

Although the device could power-on with the magnetic flux density at any level, for purposes of explanation of figure 3, start at the far left, where the magnetic flux (B, on the horizontal axis) is less positive than BRP或B.op.. Here the device is off, and the output voltage (V出去，在垂直轴上）取决于器件设计：高（顶面板）或低（底板）。

在向右朝向箭头之后，磁场变得越来越积极。当场比b比b更积极op., the device turns on. This causes the output voltage to change to the opposite state (either to high or to low, depending on the device design).

While the magnetic field remains more positive than BRP，设备保持打开，输出状态保持不变。即使B变得略低于B，这也是如此op.，在开关滞后的内置区域内，BHYS..

在向左朝向左侧箭头后，磁场变得较低。当磁场再次下降到b以下时RP, the device turns off. This causes the output to change back to the original state.

Pull-Up Resistor

上拉电阻必须连接在设备电源和输出引脚之间（参见图4）。上拉电阻的常用值范围为1至10kΩ。最小上拉电阻是霍尔IC最大输出电流的函数（通常设计为沉积电流的设备）和电源电压。20 mA是典型的最大输出电流，在这种情况下，最小上拉将是vCC/ 0.020 A.

In applications where current consumption is a concern, the pull-up resistance could be as large as 50 to 100 kΩ. Caution however is required because large pull-up values make it possible to induce external leakage currents to ground. This is not a device problem, rather the leakage occurs in the conductors between the pull-up resistor and the device output pin. These currents could be high enough to reduce the output voltage, regardless of the state of the magnetic field and device switching state. Taken to the extreme, this can reduce the output voltage enough to inhibit proper external logic functions.

Figure 4

Figure 4. Typical application diagram.

使用旁路电容器

有关旁路电容的布局，请参阅图4。一般来说：

  • For designs without chopper stabilization − It is recommended that a 0.01 µF capacitor be placed between the output and ground pins and between the supply and ground pins.
  • For designs with chopper stabilization − A 0.1 µF capacitor must be placed between the supply and ground pins, and a 0.01 µF capacitor is recommended between the output and ground pins.

Power-On Time

上电时间depends to some extent on the device design. Digital output devices, such as the unipolar switch, reach stability with the following approximate delays:

设备类型 上电时间
Without chopper-stabilization <1μs.
随着斩波稳定 <25μs.

基本上，这意味着在提供电源之后经过的经过时间之前，器件输出可能不是正确的状态，但是在经过此时间之后，设备输出被保证为正确的状态。

Power Dissipation

总功率耗散是两个因素的总和：

  • Power consumed by the Hall device, excluding power dissipated in the output. This value is VCCtimes the supply current. VCC是设备电源电压，电源电流通常在数据表上指定。例如，给定VCC= 12 V and supply current = 9 mA, power dissipation = 12 × 0.009 or 108 mW.
  • Power consumed in the output transistor. This value is V（坐了）times the output current (set by the pull-up resistor). If V（坐了）是0。4 V (worst case) and the output current is 20 mA (often worst case), the power dissipated is 0.4 × 0.02 = 8 mW. As you can see, because of the very low saturation voltage the power dissipated in the output is not a huge concern.

该示例的总功耗为108 + 8 = 116 MW。将此号码占用在问题的数据表中的额额可图中，并检查是否必须减少最大允许操作温度。

常见问题

问：如何将磁铁相对于霍尔设备定位？

答：磁铁南极针对器件包的品牌面。品牌面部是您找到设备的标识标记的位置，例如部分部件号或日期代码。

Q: How does a north polarity, or negative, magnetic field affect a unipolar switch?

答：北极性或消极，现场对单极开关没有影响。

问：我可以用磁铁向设备包接近侧面吗？

答：是的，然而牢记这一点：如果磁铁的极仍然在相同方向上保持导向，则通过装置的磁通场的取向从前侧方法保持不变（例如，如果南极是南极在前侧方法中更靠近设备，然后北极将在后侧接近靠近设备）。然后，北极将产生相对于霍尔元素的正面场，而南极会产生负场。

问：是否有权衡将设备接近侧面？

A: Yes. A "cleaner" signal is available when approaching from the package front side, because the Hall element is located closer to the front side (the package branded face) than to the back side. For example, for the "UA" package, the chip with the Hall element is 0.50 mm inside the branded face of the package, and so approximately 1.02 mm from the back-side face. (The distance from the branded face to the Hall element is referred to as the "active area depth.")

Q: Can a very strong magnetic field damage a Hall-effect device?

A: No. A very strong field will not damage an Allegro Hall-effect device nor will such a field add additional switchpoint hysteresis (other than the designed hysteresis).

问：为什么我想要一个斩波器稳定的设备？

A: Chopper-stabilized sensor ICs allow greater sensitivity with more-tightly controlled switchpoints than non-chopped designs. This may also allow higher operational temperatures. Most new device designs utilize a chopped Hall element.

Suggested Devices

Allegro UniPolar设备列在公司网站上的选择指南中，开关和闩锁。

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相关设备类型的应用说明

Reference: AN296069