锁定开关霍尔效应IC基础知识
锁定开关霍尔效应IC基础知识
There are four general categories of Hall-effect IC devices that provide a digital output: unipolar switches, bipolar switches, omnipolar switches, and latches. Latching switches are described in this application note. Similar application notes on单极开关,双极开关, and全极开关在快板上提供™ 网站。
锁存霍尔效应传感器IC，通常被称为“锁存”，是锁存输出状态的数字输出霍尔效应切换。闩锁类似于双极开关，具有正面bOPand negative BRP, but provide tight control over switching behavior. Latches require both positive and negative magnetic fields to operate. A magnet presenting a south polarity (positive) magnetic field of sufficient strength (magnetic flux density) will cause the device to switch to its on state. When the device is turned-on it latches the state and remains turned-on, even if the magnetic field is removed, until a north polarity (negative) magnetic field of sufficient strength is presented. When the negative field is presented, the device is turned-off. It latches the changed state and remains turned-off, even if the magnetic field is removed, until a south polarity (positive) magnetic field of sufficient strength is again presented.
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.
Figure 1. Two latched device applications using ring magnets. The ring magnets have alternating N (north) and S (south) polarity zones, which are rotated past the Hall devices, causing them to turn on and off.
Magnetic Switchpoint Terms
The following are terms used to define the transition points, orswitchpoints，霍尔开关操作：
图2.霍尔效应是指当施加电流受垂直磁场影响时所存在的可测量电压。
- B.−磁通密度的符号，用于确定霍尔器件开关点的磁场特性。用高斯（G）或特斯拉（T）测量。换算为1克=0.1公吨。
B有北或南极性,所以它是使用ful to keep in mind the algebraic convention, by which B is indicated as a negative value for north-polarity magnetic fields, and as a positive value for south-polarity magnetic fields. This convention allows arithmetic comparison of north and south polarity values, where the relative strength of the field is indicated by the absolute value of B, and the sign indicates the polarity of the field. For example, a − 100 G (north) field and a 100 G (south) field have equivalent strength, but opposite polarity. In the same way, a − 100 G field is stronger than a − 50 G field. - 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− BRP|。
典型的操作
The switchpoints of latching sensor ICs are symmetrical around the neutral field level, B = 0 G, as shown in figure 3. The switchpoints are at equal field strengths, but at opposite polarities. For example, if the operate point, BOP, is 85 G (a positive value indicating south polarity), the release point, BRP，是 - 85克（指示北极的负值）。锁存最新状态可防止设备在受弱区内切换。
锁定开关在强的南极性场中接通，结果输出信号是低电平的（在输出晶体管饱和电压，V出去(sat)通常<200 mV）。锁定开关在强北极极性场中关闭，结果输出信号处于逻辑高（达到全电源电压，VCC）。由于开关状态被锁定，因此在磁场处于开关点滞后范围内，这些设备不会切换，因为B之间OPand BRP。B.ecause the 0 G point must be crossed before switching occurs in either direction, the hysteresis range is relatively wider than for other types of Hall switches.
图3.。Latching switch output characteristics. The device output switches to logic low in the presence of a strong south polarity field, and switches to logic high in a strong north polarity field. In a weak field, the latch does not change output state.
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 BRPor BOP。这里的设备关闭，输出电压（V.出去在垂直轴上）高。
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，设备亮起。这使得输出电压变为相反的状态，低。
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.。
在向左朝向左侧后，磁场变得更少，然后更负。当磁场再次下降到b以下时RP，设备关闭。这会导致输出更改回原始状态。
磁铁
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。在需要考虑电流消耗的情况下，上拉电阻可能高达50到100 kΩ。注意：当上拉值较大时，可能会导致外部泄漏电流接地，即使在设备磁关闭的情况下，也足以降低输出电压。这不是设备问题，而是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。极端情况下，这会降低传感器IC输出电压，足以抑制正常的外部逻辑功能。
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 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 State
A latch powers-on in a valid state only if the magnetic field strength exceeds either BOPor BRPwhen power is applied. If the magnetic field strength is in the hysteresis band, that is between BOPand BRP，该设备最初可以假设开启或关闭状态，然后在第一次偏移之外的正确状态以超出SwitchPoint来实现。设备可以设计为带电源启动逻辑，直到达到SwitchPoint之前将设备设置为OFF。
Power-On Time
上电时间取决于设备设计的一定程度。数字输出传感器IC，如锁存装置，在下面的时间内达到初始电源的稳定性。
| 设备类型 | 上电时间 |
|---|---|
| 非切碎的设计（如A1210家族） | <4μs. |
| Chopper-stabilized (such as A1220 family) | <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：
- 传感器IC消耗的功率，排除在输出中消耗的功率。这个值是vCCtimes the supply current. VCCis the device supply voltage and the supply current is specified on the datasheet. For example, given VCC= 12 V和电源电流= 9 mA。功率耗散= 12×0.009或108 MW。
- Power consumed in the output transistor. This value is V(on)(sat)输出电流（由上拉电阻设置）。如果V.(on)(sat)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：我如何定位磁铁？
答：磁极磁极朝向器件的品牌面向定向。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。
问：我可以用磁铁向侧面接近设备吗？
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 large field damage a Hall-effect device?
A: No. A very large field will not damage an Allegro Hall-effect device nor will such a field add additional 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.
建议的设备
Standard Allegro latches are listed in the selection guides on the company website, atHall-Effect Latches/Bipolar Switches。
低功耗锁存器列于微功率开关/闩锁。
Possible Applications
- Speed sensing
- 旋转编码器
- 革命计数
- 流量计
- 无刷电机换向
- 防夹天窗/车窗提升电机换向
相关设备类型的应用说明
Reference: AN296067