Bipolar Switch Hall-Effect ICs

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。在本应用笔记中描述了双极交换机。类似的应用笔记unipolar switches,omnipolar switches，和latches提供在Allegro™网站上。

双极传感器IC设计为敏感开关。（注意术语“双极”是指磁极极度，并且与双极半导体芯片结构无关。）双极开关具有一致的滞后，但各个单元具有相对更正或更多负范围的开关点。这些设备在使用紧密，交替的北极和南极的应用中找到了最小所需的磁信号幅度，ΔB，因为磁场极性的交替确保切换，并且一致的滞后确保周期性。

Applications for detecting the position of a rotating shaft, such as in a brushless dc motor (BLDC) 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 bipolar switch device. When the shaft rotates, the magnetic zones are moved past the Hall device. The device is subjected to the nearest magnetic field and is 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 bipolar 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.

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:

图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 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− 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_op.）。所得到的设备输出状态取决于各个设备电子设计。
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. B_HYS= | B_op.- B._RP|.

典型的操作

双极交换机通常具有正面b_op.和负面B._RP, but these switchpoints occur at field strength levels that are not precisely symmetrical with respect to the neutral level, B = 0 G. This characteristic is allowed so bipolar switches can provide greater sensitivity and narrower B_HYSthan latching switches (bipolar switches were originally conceived as a lower-cost alternative to early latches). A small percentage (≈10%) of bipolar switches have switchpoint ranges entirely in the positive (south) polarity range or entirely in the negative (north) polarity range. All of these characteristic ranges can be reliably operated using alternating positive (south) and negative (north) polarity fields. Turn-off will usually occur when the magnetic field is removed, but to ensure release, a field reversal is required.

An example of a bipolar switch would be a device with a maximum operate point, B_op.(max), of 45 G, a minimum release point, B_RP(min), of –40 G, and a minimum hysteresis, B_HYS(min), of 15 G. However, the minimum operate point, B_op.(min), could be as low as –25 G, and the maximum release point, B_RP（最大值），可以高达30 G.图3显示了具有这些开关点的假设装置的单位的这些特性。在图3的顶部，迹线“最小ΔB”演示了振幅可以导致可靠的切换的程度。

Figure 3. Demonstration of possible switchpoint ranges for a bipolar switch, for use with low magnetic flux amplitude, narrow pitch alternating pole targets

Figure 3 illustrates the variances between the three general operating modes of bipolar switches:

"latch mode" describes any bipolar switch unit with a positive B_op.和负面B._RP, behaving like a Hall latching switch by requiring both magnetic fields to be present for complete operation (but without actual latching of the device state)
"unipolar mode" describes any bipolar switch unit with both B_op.和B._RP在e positive (south) range
"negative unipolar mode" (sometimes referred to as "negative switch" mode) describes any bipolar switch unit with both B_op.和B._RP在e negative (north) range

The release point flux density becomes less important because, if the Hall switch has not switched when the pole has passed and the flux density approaches the neutral level, B = 0 G, the switch will certainly turn off when the following pole increases the flux density in the opposite polarity. Bipolar Hall switches take advantage of this extra margin in release-point flux values to achieve lower operate-point flux densities, a definite advantage in ring magnet applications.

As can be seen in the V_OUTtraces at the bottom of figure 3, for each of these modes, switching at each pole alternation is reliable, with the duty cycle of the output differing somewhat according to the operating mode. A bipolar device operating in latch mode has nearly symmetrical switchpoints. This tends to set the duty cycle to near perfection when working with equally-spaced ring magnet poles. Having said that, even if the switchpoints were skewed, the duty cycle will still be close to 50% on and 50% off. For motor commutation this is ideal, resulting in high efficiency. Units having unipolar mode turn on and off with the south pole and do nothing as the north pole passes. Units in this mode will have a duty cycle of perhaps 40% on and 60% off. Units in negative unipolar mode turn off and on with the north pole and do nothing as the south pole passes. Units in this mode will have a duty cycle of perhaps 60% on and 40% off.

The three panels of figure 4 show the transfer characteristics of the operating modes of bipolar sensor ICs.

Figure 4a

图4A。锁存模式特征。请注意，SwitchPoint磁滞区B_HYS，包括中性磁通密度水平，B = 0 g。

For purposes of explanation of figure 4A, assume the device powers-on with the magnetic flux density at the far left, where the magnetic flux (B, on the horizontal axis) is more negative than B_RPor B_op.. Here the device is off, and the output voltage (V_OUT, 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_op., the device turns on. This causes the output voltage to change to the opposite state, low.
While the magnetic field remains more positive than B_RP，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, B_HYS.
Following the arrows back toward the left, the magnetic field becomes less positive and then more negative. When the magnetic field again drops below B_RP, the device turns off. This causes the output to change back to the original state, high.

Figure 4b

出于图4B的说明的目的，假设设备为磁通密度在左侧的磁通密度，其中磁通量（B，水平轴线上）比B较小为正_RPor B_op.. Here the device is off, and the output voltage (V_OUT, 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_op., the device turns on. This causes the output voltage to change to the opposite state, low.
While the magnetic field remains more positive than B_RP，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, B_HYS.
Following the arrows back toward the left, the magnetic field becomes less positive. When the magnetic field again drops below B_RP, the device turns off. This causes the output to change back to the original state, high.

Figure 4c

Figure 4C. Negative unipolar (negative switch) mode characteristic. Note that the switchpoint hysteresis zone, B_HYS, is entirely more magnetically north than the neutral flux density level, B = 0 G. A south magnetic field has no effect on the device, although it can aid switching by dissipating any flux remaining after a north field has passed.

For purposes of explanation of figure 4C, assume the device powers-on with the magnetic flux density at the far left, where the magnetic flux (B, on the horizontal axis) is more negative than B_RPor B_op.. Here the device is off, and the output voltage (V_OUT, on the vertical axis) is high.
Following the arrows toward the right, the magnetic field becomes less negative. When the field is less negative than B_op., the device turns on. This causes the output voltage to change to the opposite state, low.
While the magnetic field remains less negative than B_op.，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, B_HYS.
Following the arrows back toward the left, the magnetic field becomes less positive. When the magnetic field again drops below B_RP, the device turns off. This causes the output to change back to the original state, high.

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 V_CC/ 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。

图5。典型的程序图。

Use of Bypass Capacitors

Refer to figure 5 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.

开机状态

仅当磁场强度超过B时，双极设备才能以有效状态为动力_op.或者小于b_RPwhen power is applied. If the magnetic field strength is in the hysteresis band, that is between B_op.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.

开机状态s
Sensor IC Type	开机状态(0 G Field)
Unipolar Switch	Off
Latch	Either state^1,2
负面开关	上²
¹Unless power-on logic is incorporated in the design. ²Unless power-on of the device occurs while the magnetic field is inside the specified magnetic hysteresis of the device.

Power-On Time

Power-on time depends to some extent on the device design. Digital output sensor ICs, such as the bipolar device, reach stability on initial power-on in the following times.

Device type	Power-on time
Non-chopped designs	<4 µs
Chopper-stabilized	<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 V_CC“透明国际”mes the supply current. V_CCis the device supply voltage and the supply current is specified on the datasheet. For example, given V_CC= 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）}“透明国际”mes the output current (set by the pull-up resistor). If V_{（开）（坐）}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.

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?

磁铁的两极是面向品牌ed 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?

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).

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

Allegro双极交换机列在公司网站上的选择指南中，ATHall-Effect Latches and Bipolar Switches.

可能的应用程序亚博尊贵会员

无刷直流电机旋转
速度感应
Pulse counters, encoders
Automotive

Application Notes on Related Device Types

Reference: AN27705