质量标准和环境认证

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

下载PDF版本

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bipolar switches,全极开关, andlatchesare provided on the Allegro website.

Unipolar Hall-effect sensor ICs, often referred to as "unipolar switches," are operated by a positive magnetic field. A single magnet presenting a south polarity (positive) magnetic field of sufficient strength (magnetic flux density) will cause the device to switch to its on state. After it has been turned-on, the unipolar IC will remain turned-on until the magnetic field is removed and the IC reverts to its off state.

阿明费申请检测的位置icle gear-shift lever is shown in figure 1. The gear-shift lever incorporates a magnet (the red-and-blue cylinder). The line of miniature black boxes is an array of unipolar switch devices. When the vehicle operator moves the lever, the magnet is moved past the individual Hall devices. The devices near the magnet are subjected to the magnetic field and are turned-on, but more remote devices are not affected and remain turned-off. Note that the south pole of the magnet (colored red) is toward the Hall devices, and that the Hall devices are oriented with the branded face of the device toward the magnet south pole.

Figure 1

Figure 1. An application using unipolar switch sensor ICs. The ultra-small Hall ICs switch as the magnet (red and blue cylinder) moves past them during gear-shifting.

Magnetic Switchpoint Terms

The following are terms used to define the transition points, orswitchpoints, 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.− The symbol for Magnetic Flux Density, the property of a magnetic field used to determine Hall device switchpoints. Measured in gauss (G) or tesla (T). The conversion is 1 G = 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). The resulting state of the device output depends on the individual device electronic design.
  • 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− BRP|。

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, the device remains turned-on, and the output state remains unchanged. This is true even if B becomes slightly less positive than BOP，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

Refer to figure 4 for a layout of bypass capacitors. In general:

  • 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 <1 µs
随着斩波稳定 <25 µs

B.asically, this means that prior to this elapsed time after providing power, device output may not be in the correct state, but after this time has elapsed, device output is guaranteed to be in the correct state.

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.

Total power dissipation for this example is 108 + 8 = 116 mW. Take this number to the derating chart in the datasheet for the package in question and check to see if the maximum allowable operational temperature must be reduced.

常见问题

问：如何将磁铁相对于霍尔设备定位？

A: The magnet south pole is directed towards the branded face of the device package. The branded face is where you will find the identification markings of the device, such as partial part number or date code.

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。

Q: Can I approach the device package back side with the magnet?

A: Yes, however bear this in mind: if the poles of the magnet remain oriented in the same direction, then the orientation of the flux field through the device remains unchanged from the front-side approach (for example, if the south pole was nearer the device in the front-side approach, then the north pole would be nearer the device in the back-side approach). The north pole would then generate a positive field relative to the Hall element, while the south pole would generate a negative field.

Q: Are there trade-offs to approaching the device back side?

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 devices are listed in the selection guides on the company website, at开关和闩锁。

亚博尊贵会员

相关设备类型的应用说明

Reference: AN296069