万能开关霍尔效应IC基础知识
万能开关霍尔效应IC基础知识
Introduction
There are four general categories of Hall-effect IC devices that provide a digital output: unipolar switches, bipolar switches, omnipolar switches, and latches. Omnipolar switches are described in this application note. Similar application notes onbipolar switches,单极开关, and闩锁are provided on the Allegro™ website.
Omnipolar Hall-effect sensor ICs, often referred to as "omnipolar switches," are a type of digital output Hall-effect latching switches that operate with either a strong positive or strong negative magnetic field. This simplifies application assembly because the operating magnet can be mounted with either pole toward the omnipolar device. A single magnet presenting a field of sufficient strength (magnetic flux density) will cause the device to switch to its on state. After it has been turned-on, the omnipolar IC will remain turned-on until the magnetic field is removed and the IC reverts to its off state. It latches the changed state and remains turned-off, until a magnetic field of sufficient strength is again presented.
An application for detecting the position of a vehicle gear-shift lever is shown in figure 1. The gear-shift lever incorporates a magnet (the purple cylinder). The line of miniature black boxes is an array of omnipolar 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. Either the south pole or the north pole of the magnet can be oriented toward the Hall devices, and the branded face of the Hall device package is toward the magnet.
图1。An application using omnipolar switch sensor ICs. The ultra-small Hall ICs switch as the magnet (purple cylinder) moves past them during gear-shifting.
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– 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，-100g（北）字段和100克（南）字段具有等效强度，但极性相反。以同样的方式，-100g字段比-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). The resulting state of the device output depends on the individual device electronic design.
- 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− BRP|。
典型的操作
The switchpoint ranges of omnipolar sensor ICs are symmetrical around the neutral field level, B = 0 G, as shown in figure 3. The switchpoints are at equivalent field strengths, but at opposite polarities. For example, assume the positive (south) polarity switchpoints were operate point, BOP（s）60克，释放点，bRP(S), 30 G. Then the negative (north) polarity switchpoints would be operate point, BOP(N)−60克,并释放点,BRP（n）, −30 G. Latching the latest state prevents the devices from switching while subject to weak fields.
OmniPolar开关在任一极性的强磁场中打开，所产生的输出信号可以在逻辑高（直至全电源电压，VCC）或逻辑低（在输出晶体管饱和电压，V出去(sat), usually <200 mV), depending on the design of the device IC output stage. An omnipolar switch turns off in a moderate magnetic field, and the resulting output signal is the opposite of the polarity in the on state. Like other types of Hall digital switch, these devices do not switch while the magnetic field strength is in the switchpoint hysteresis ranges, BHYS。此外，锁存开关状态防止设备切换，而磁场相对较弱，则在释放点之间，B之间RP（n）and BRP(S)。It is not necessary for the 0 G point to be crossed before switching can occur again. A given switching event can be followed by a switching event of either the same or the opposite polarity.
图3.。Omnipolar switch output characteristics. The top panel displays switching to logic high in the presence of a strong magnetic field, and the bottom panel displays switching to logic low, also in a strong magnetic field.
虽然该装置可以在任何级别的磁通密度上接通，但是对于图3的说明，距离左侧的开始，其中磁通（B，水平轴上）比北极性更负点，B.OP(N)。这里的设备接通，输出电压（V出去, on the vertical axis) depends on the device design: high (top panel), or low (bottom panel).
在向右箭头之后，磁场变得更少。当场比b弱RP（n），设备关闭。这使得输出电压变为相反状态（其高或低，根据器件设计）。
While the magnetic field remains weaker than BOP(N)and BOP（s）(near B = 0 G, the center of figure 3), the device remains turned-off, and the latched output state remains unchanged. This is true even if B becomes slightly stronger than BRP（n）or BRP(S), within the built-in zone of switching hysteresis, BHYS。
At the next strong magnetic field, if it is positive, following the arrows toward the right, the magnetic field becomes more positive. When the field is stronger than BOP（s），设备亮起。这使得输出电压变为相反状态（其高或低，根据器件设计）。如果相反，接下来的强磁场是负的，则在朝向左侧箭头后，磁场变得更加负。当场比b强OP(N)，设备亮起。这导致输出电压返回到原始状态。
拉动电阻
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. In cases where current consumption is a concern, the pull-up resistance could be as large as 50 to 100 kΩ. Caution: With large pull-up values it is possible to invite external leakage currents to ground, which are high enough to drop the output voltage even when the device is magnetically off. This is not a device problem but is rather a leakage that occurs in the conductors between the pull-up resistor and the sensor ICs output pin. Taken to the extreme, this can drop the sensor IC output voltage enough to inhibit proper external logic function.
图4.。Typical application diagram.
使用旁路电容器
请参考to figure 4 for a layout of bypass capacitors. In general:
- 对于没有斩波稳定的设计 - 建议将0.01μF电容放在输出和接地引脚之间以及供电和接地销之间。
- 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
An omnipolar device 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。
上电时间
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。
| Device type | Power-on time |
|---|---|
| Non-chopped designs | <4 µs |
| 斩波稳定 | <25 µs |
Basically, 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)is 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？
答：斩波稳定的传感器IC允许比非切碎的设计更加紧密控制的开关点更大的灵敏度。这也可能允许更高的操作温度。大多数新设备设计利用切碎的霍尔元素。
建议的设备
Standard Allegro latches are listed in the selection guides on the company website, at霍尔效应锁存双极开关。
低功耗锁存器列于微功率开关/闩锁。
Possible Applications
- 手机
- Cordless telephones
- 奉献者
- Palmtop computers
相关设备类型的应用说明
请参考ence: AN296070