Unipolar Hall-Effect Sensor IC Basics
Unipolar Hall-Effect Sensor IC Basics
There are four general categories of Hall-effect IC devices that provide a digital output: unipolar switches, bipolar switches, omnipolar switches, and latches. Unipolar switches are described in this application note. Similar application notes onbipolar switches那omnipolar switches那and闩锁are 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.
图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.，霍尔开关操作：
图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.can have a north or south polarity, so it is useful 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− 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.
- B.rp.- 磁释放点;霍尔器件关闭的弱化磁场的水平（或用于某些类型的霍尔设备，给出阳性b的强化负面的水平OP). The resulting state of the device output depends on the individual device electronic design.
- B.HYS− 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.OP− Brp.|.
典型的操作
When a unipolar switch turns on, the resulting output signal can be either at logic high or logic low, depending on the design of the device IC output stage. Figure 3 shows the possible output states of unipolar switches. The top panel represents a switch designed to output logic low (at the output transistor saturation voltage, V出（坐）那usually <200 mV) in a strong south polarity field. The bottom panel represents a switch designed to output logic high (up to full supply voltage, VCC.在相同的条件下)。
图3.。Unipolar switch output characteristics. The top panel displays switching to logic low in the presence of a strong south polarity field, and the bottom panel displays switching to logic high, also in a south polarity field.
尽管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，尽管在左侧的距离开始，但是磁通量（水平轴上）的磁通（B，水平轴上）的偏置率小于brp.or BOP。这里的设备关闭，输出电压（V.OUT那on the vertical axis) depends on the device design: high (top panel), or low (bottom panel).
Following the arrows toward the right, the magnetic field becomes increasingly positive. When the field is more positive than BOP，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）。
虽然磁场比b更积极rp.,e device remains turned-on, and the output state remains unchanged. This is true even if B becomes slightly less positive than BOP那within the built-in zone of switching hysteresis, BHYS。
Following the arrows back toward the left, the magnetic field becomes less positive. When the magnetic field again drops below Brp.,e device turns off. This causes the output to change back to the original state.
拉动电阻
A pull-up resistor must be connected between the device supply and the output pin (see figure 4). Common values for pull-up resistors range from 1 to 10 kΩ. The minimum pull-up resistance is a function of the Hall IC maximum output current (the devices usually are designed to sink current) and the supply voltage. 20 mA is a typical maximum output current, and in that case the minimum pull-up would be VCC./ 0.020 A.
在电流雷竞技最新网址消耗是一个问题的应用中，上拉电阻可以大至50至100kΩ。然而，需要注意，因为大的上拉值可以使外部泄漏电流诱导到地面。这不是设备问题，而是在上拉电阻器和器件输出引脚之间的导体中发生泄漏。无论磁场和器件切换状态如何，这些电流都足够高以降低输出电压。采取至极端，这可以减少输出电压，足以抑制适当的外部逻辑功能。
图4.典型的应用程序图。
Use of Bypass Capacitors
Refer 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。
- 对于具有斩波稳定的设计 - 电源和接地引脚之间必须放置0.1μF电容，并且在输出和接地引脚之间建议使用0.01μF电容。
上电时间
上电时间取决于设备设计的一定程度。数字输出设备，如单极开关，达到稳定性，具有以下近似延迟：
| Device type | Power-on time |
| 没有切碎机稳定 | <1 µs |
| With chopper-stabilization | <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.
功耗
Total power dissipation is the sum of two factors:
- 大厅设备消耗的功率，排除在输出中消耗的功率。这个值是vCC.电源电流的时间。V.CC.is the device supply voltage and the supply current is usually 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。
- 输出晶体管中消耗的功率。这个值是v(sat)输出电流（由上拉电阻设置）。如果V.(sat)是0.4 V（最坏情况），输出电流为20 mA（通常最坏情况），功耗耗散为0.4×0.02 = 8兆瓦。正如您所看到的，因为饱和电压非常低，输出中的功率不受巨大的关注。
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.
经常问的问题
Q: How do I orient the magnet relative to the Hall device?
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.
问：北极性或负面磁场如何影响单极开关？
A: A north polarity, or negative, field has no effect on a unipolar switch.
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?
答：是的。从包装前侧接近时，可以使用“清洁剂”信号，因为霍尔元件位于靠近前侧（封装品牌面部）而不是背面。例如，对于“UA”封装，带有霍尔元件的芯片在包装的品牌面内为0.50毫米，距离后侧面积约为1.02毫米。（从品牌面对霍尔元素的距离被称为“有源区域深度”。）
问：是否有一个非常强大的磁场损坏了霍尔效应装置？
答：不可以。一个非常强大的字段不会损坏Allegro霍尔效应装置，也不会这样一个字段添加额外的SwitchPoint滞后（除了设计的滞后）。
Q: Why would I want a chopper-stabilized device?
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。
Suggested Devices
Allegro unipolar devices are listed in the selection guides on the company website, atraybet56
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- 叶片interpupter切换
- 接近感应
- Seat position sensing
- 安全带扣感应
- Open/close door or lid sensing
- 脉冲柜台
- raybet12
- Speed sensing
Application Notes on Related Device Types
参考：AN296069.