Latching Switch Hall-Effect IC Basics
Latching Switch Hall-Effect IC Basics
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。锁存开关在本应用笔记中描述。类似的应用笔记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 Bop.和负面B.RP，但提供对切换行为的紧密控制。闩锁需要正面和负磁场来操作。呈现足够强度（磁通密度）的南极（正）磁场的磁铁将导致装置切换到其上的状态。当该设备接通时，它锁存状态并保持接通，即使磁场被移除，直到呈现足够强度的北极性（负）磁场。当呈现否定字段时，设备已关闭。它锁存了改变的状态并保持关闭，即使磁场被移除，直到再次呈现足够强度的南极（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器件应用。雷竞技最新网址环形磁铁具有交替的n（北）和s（南）极性区域，它们通过霍尔设备旋转，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，或者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。 - Bop.− 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 Bop.）。所得到的设备输出状态取决于各个设备电子设计。
- 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= | Bop.- B.RP|.
典型的操作
锁存传感器IC的开关点围绕中性场级对称，B = 0 g，如图3所示。开关点处于等于场强，但在极性相反。例如，如果操作点，Bop., 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 Bop.和B.RP。因为在切换之前必须交叉0g点，所以滞后范围比其他类型的霍尔开关相对宽。
图3.锁存开关输出特性。在强大的南极性场的存在下，设备输出到逻辑低电平，并在强大的北极极性场中切换到逻辑高。在弱字段中，锁存器不会改变输出状态。
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.op.。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 Bop., 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变得略低于B，这也是如此op., 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
仅当磁场强度超过B时，锁存电源op.或B.RPwhen power is applied. If the magnetic field strength is in the hysteresis band, that is between Bop.和B.RP, 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家族） | <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
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）（坐）times the output current (set by the pull-up resistor). If V（开）（坐）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
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?
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 large field damage a Hall-effect device?
答：不，非常大的领域不会损坏Allegro霍尔效应装置，也不会这样的场地添加额外的滞后（除了设计的滞后）。
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霍尔效应闩锁/双极开关。
Low-power latches are listed atMicropower Switches/Latches。
可能的应用程序雷竞技最新网址
- 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