Latching Switch Hall-Effect IC Basics
Latching Switch Hall-Effect IC Basics
提供数字输出的霍尔效应IC器件有四大类：单极性开关、双极性开关、全极性开关和锁存器。本应用说明中描述了闭锁开关。类似应用说明unipolar switches,双极交换机，和omnipolar switches提供在Allegro™网站上。
Latching Hall-effect sensor ICs, often referred to as "latches," are digital output Hall-effect switches that latch output states. Latches are similar to bipolar switches, having a positive B操作和阴性BRP，但提供对切换行为的严格控制。闩锁需要正负磁场才能工作。呈现足够强度（磁通密度）的南极（正）磁场的磁铁将使设备切换到其开启状态。当设备开启时，它会锁定状态并保持开启状态，即使磁场被移除，直到出现足够强度的北极（负）磁场。当负电场出现时，设备关闭。它锁定改变的状态并保持关闭，即使磁场被移除，直到再次出现足够强度的南极（正）磁场。
Applications for detecting the position of a rotating shaft are shown in figure 1. The multiple magnets are incorporated into a simple structure referred to as a "ring magnet," which incorporates alternating zones of opposing magnetic polarity. The IC package adjacent to each ring magnet is the Hall latch device. When the shaft rotates, the magnetic zones are moved past the Hall device. The device is subjected to the nearest magnetic field and are turned-on when a south field is opposite, and turned-off when a north field is opposite. Note that the branded face of the device is toward the ring magnet.
图1。使用环形磁铁的两个锁存设备应用。环形磁铁有交替的N（雷竞技最新网址北）和S（南）极性区，这些极性区经过霍尔器件旋转，导致它们打开和关闭。
磁性开关点术语
以下是用于定义过渡点的术语，或switchpoints, of Hall switch operation:
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可以有一个北极或南极，因此记住代数惯例是有用的，根据这个惯例，B表示为北极磁场的负值，而表示为南极磁场的正值。这个惯例允许对南北极性值进行算术比较，其中磁场的相对强度由B的绝对值表示，符号表示磁场的极性。例如，−100 G（北）磁场和100 G（南）磁场强度相等，但极性相反。同样地，−100 G磁场比−50 G磁场强。 - B操作− Magnetic operate point; the level of a strengthening magnetic field at which a Hall device switches on. The resulting state of the device output depends on the individual device electronic design.
- BRP− 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 B操作). 设备输出的结果状态取决于单个设备的电子设计。
- BHYS− Magnetic switchpoint hysteresis. The transfer function of a Hall device is designed with this offset between the switchpoints to filter out small fluctuations in the magnetic field that can result from mechanical vibration or electromagnetic noise in the application. BHYS= | B操作−B级RP|.
典型的操作
闭锁传感器IC的开关点围绕中性场电平B=0 G对称，如图3所示。开关点的场强相等，但极性相反。例如，如果操作点操作, is 85 G (a positive value indicating south polarity), the release point, BRP, is − 85 G (a negative value indicating north polarity). Latching the latest state prevents the devices from switching while subject to weak fields.
A latching switch turns on in a strong south polarity field, and the resulting output signal is logic low (at the output transistor saturation voltage, VOUT(sat), usually <200 mV). A latching switch turns off in a strong north polarity field, and the resulting output signal is at logic high (up to full supply voltage, VCC). Because the switched state is latched, these devices do not switch while the magnetic field is in the switchpoint hysteresis range, between B操作和BRP. 由于0g点必须在两个方向上发生切换之前穿过，因此滞后范围比其他类型的霍尔开关要宽。
图3。闭锁开关输出特性。当存在强南极磁场时，器件输出切换到逻辑低电平；当存在强北极磁场时，器件输出切换到逻辑高电平。在弱场中，锁存器不改变输出状态。
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操作. Here the device is off, and the output voltage (VOUT, on the vertical axis) is high.
Following the arrows toward the right, the magnetic field becomes increasingly positive. When the field is more positive than B操作, the device turns on. This causes the output voltage to change to the opposite state, low.
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变得比B略弱，这也是正确的操作, within the built-in zone of switching hysteresis, BHYS.
Following the arrows back toward the left, the magnetic field becomes less positive and then more negative. When the magnetic field again drops below BRP, the device turns off. This causes the output to change back to the original state.
Magnets
Individual magnets may be used to provide the two opposing magnetic polarities, however, it is usually more cost effective to use ring or strip magnet material. Ring and strip magnets are magnetized with alternating poles with specified spacing. A ring magnet is a toroid- or disc-shaped assembly (see figure 1) with alternating radially- or axially-magnetized poles. A strip magnet is a flat strip with alternating magnetic poles. Ring magnets are available in a variety of materials including ceramic, rare earth, and flexible materials. Strip magnets nearly always utilize flexible materials such as Nitrile rubber binder containing oriented barium ferrite, or higher energy rare-earth materials.
Ring magnets normally are specified as having a number of poles while strip magnets are normally specified in poles-per-inch. A four-pole ring magnet contains two north and two south oriented alternating poles (N-S-N-S) while an 11 pole-per-inch strip magnet has alternating poles spaced on 0.0909-in. centers. A variety of pole spacings are available from magnet manufacturers.
Pull-Up Resistor
A pull-up resistor must be connected between the positive supply and the output pin (see figure 4). Common values for pull-up resistors are 1 to 10 kΩ. The minimum pull-up resistance is a function of the sensor IC maximum output current (sink current) and the actual supply voltage. 20 mA is a typical maximum output current, and in that case the minimum pull-up would be VCC/ 0.020 A.如果电流消耗是一个问题的情况下，上升电阻可能大约50至100kΩ。小心：具有大的上拉值，可以邀请外部泄漏电流接地，即使当器件磁性关闭时，也足以降低输出电压。这不是设备问题，而是相当是在上拉电阻器和传感器IC输出引脚之间的导体中发生的泄漏。采取至极端，这可以缩小传感器IC输出电压，足以抑制适当的外部逻辑功能。
Figure 4. Typical application diagram.
Use of Bypass Capacitors
有关旁路电容器的布局，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 the output and ground pins and between the supply and ground pins.
- 设计的直升机稳定−0.1µFcapacitor must be placed between the supply and ground pins, and a 0.01 µF capacitor is recommended between the output and ground pins.
开机状态
只有当磁场强度超过B或B时，闩锁才会在有效状态下通电操作或BRPwhen power is applied. If the magnetic field strength is in the hysteresis band, that is between B操作和BRP, the device can assume either an on or off state initially, and then attains the correct state at the first excursion beyond a switchpoint. Devices can be designed with power-on logic that sets the device off until a switchpoint is reached.
Power-On Time
Power-on time depends to some extent on the device design. Digital output sensor ICs, such as the latching device, reach stability on initial power-on in the following times.
| Device type | Power-on time |
|---|---|
| Non-chopped designs (such as A1210 family) | <4 µs |
| 斩波稳定（如A1220系列） | <25微秒 |
基本上，这意味着在提供电源之后的这段时间之前，设备输出可能不处于正确的状态，但是在这段时间之后，设备输出保证处于正确的状态。
Power Dissipation
Total power dissipation is the sum of two factors:
- Power consumed by the sensor IC, excluding power dissipated in the output. This value is VCCtimes the supply current. VCCis the device supply voltage and the supply current is specified on the datasheet. For example, given 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（开）（周六）times the output current (set by the pull-up resistor). If V（开）（周六）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.
本例的总功耗为108+8=116MW。将此数字记录到相关包装数据表中的降额表中，并检查是否必须降低最大允许工作温度。
常见问题
Q: How do I orient the magnets?
A: The magnet poles are oriented towards the branded face of the device. The branded face is where you will find the identification markings of the device, such as partial part number or date code.
Q: Can I approach the device back side with the magnet?
A： 是的，但是要记住：如果磁铁的磁极保持在同一方向上，那么穿过装置的磁场方向与正面进近保持不变（例如，如果南极在正面进近时更接近装置，然后，北极将更接近背面接近的装置）。北极将产生一个相对于霍尔元件的正磁场，而南极将产生一个负磁场。
Q： 接近设备背面是否有权衡？
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 large field damage a Hall-effect device?
A： 不会。一个非常大的磁场不会损坏Allegro霍尔效应装置，这样的磁场也不会增加额外的磁滞（除了设计的磁滞）。
Q: Why would I want a chopper-stabilized device?
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
Standard Allegro latches are listed in the selection guides on the company website, at霍尔效应锁存器/双极开关.
Low-power latches are listed atMicropower Switches/Latches.
可能的应用雷竞技最新网址
- 速度感应
- Rotary encoder
- Revolution counting
- Flow meter
- Brushless motor commutation
- 防捏天窗/窗升电机换向
Application Notes on Related Device Types
Reference: AN296067