Air-Gap-Independent Speed and Direction Sensing Using the Allegro A1262

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By Stefan Kranz,
Allegro MicroSystems, LLC

Introduction

这A1262集成电路是超敏感的双通道霍尔效应闩锁。与传统的双通道闩锁一样，A1262的正交输出表示旋转环形磁体目标的旋转方向和位置/速度。然而，它在使用垂直霍尔技术的使用中以振幅来感测磁场方向。

这A1262 contains a conventional planar Hall element to derive one channel and a vertical Hall element to derive the other channel. The result is that the A1262 is capable of generating quadrature output signals (≈90° phase difference) where the phase separation is largely independent of the air gap, ring magnet size, or pole spacing. This provides an unprecedented level of flexibility for the system designer in selecting the ring magnet and its position and orientation relative to the sensor. Its small (SOT23-5) package replaces a pair of conventional Hall-effect latches, saving space and component count.

Case Studies

本应用笔记将重点关注的两个男人y possible system configurations. In both cases, the A1262LLHLT‑T device is assumed to use the Z sensing direction for the planar Hall element, and Y for the vertical Hall element (see Figure 1). An alternative version of the A1262, the A1262LLHLT‑X‑T, is also available with sensitivity in the Z and X directions. Detailed information on the A1262 can be found in the A1262 datasheet and other related application notes.

图1: A1262 Sensing Directions

In both cases, the target is a ferrite ring magnet with identical overall dimensions. In Case 1, the magnet is a multipole ring magnet. In Case 2, it is a diametrically magnetized (1 pole-pair) ring magnet (See Photo 1).

照片1: Ring Magnet

情况1: Multipole Ring Magnet

在这种情况下，目标是具有以下特征的环形磁体：

Outer diameter: 13 mm
内径：6毫米
Height: 4 mm
Pole-pairs: 4
材料：铁氧体Y10T，BR：≥0.2吨
Magnetization: Radial

图2: Mechanical Configuration for Case 1

这radial and tangential magnetic fields versus air gap around the Case 1 ring magnet are shown in Figure 3 and Figure 4. The radial field component excites the A1262 planar Hall element and is shown as the Z direction. The vertical Hall element responds to the tangential magnetic field; this is displayed as Y direction.

图3.: Radial B-Field Multipole Ring Magnet vs. Air Gap

图4.: Tangential B-Field Multipole Ring Magnet vs. Air Gap

图5.: Radial / Tangential B-Field Multipole Ring Magnet vs. Air Gap

如图3和图4所示，两个通道中的每一个的磁峰的位置相对于另一个通道非常一致。气隙几乎没有变化。图5更清楚地示出了仅显示最小和最大空气间隙，1.5和5.0mm的结果。

图6：A1262多极环形磁铁OUTA（径向）与气隙

图7.: A1262 Multipole Ring Magnet OUTB (tangential) vs. Air Gap

图6.and Figure 7 show the magnetic switching behavior of the two sensor outputs with the 8-pole ring magnet. Given the normal variation in the magnetic switchpoints of the A1262 and a large variation in air gap, the phase relationship of OUTA and OUTB remain very stable. This level of air gap independence is unique to the A1262.

As shown in Table 1 below, both outputs also maintain near-ideal (≈50%) duty cycle independent of air gap.

Table 1: Duty Cycle vs. Air Gap for Case 1

Air Gap (mm)	OUTA Duty Cycle (%)	OUTB Duty Cycle (%)
1.5	49.71.	49.83
2.0	49.77	50.00
2.5	49.77	49.60
3.0	49.71.	49.83
3.5	49.71.	49.88
4.0	49.54	49.83
4.5	49.88	49.48
5.0	49.65	49.71.

案例2.: Diametric Ring Magnet

在这种情况下，目标是具有与壳体1相同尺寸和与壳体相同的环磁体，但只有一组磁极：

Outer diameter: 13 mm
内径：6毫米
磁铁高度：4毫米
Pole-pairs: 1
材料：铁氧体Y10T，BR：≥0.2吨
Magnetization: Diametric

图8.: Mechanical Configuration for Case 2

图8示出了壳体2的机械结构。图9和图10中所示的径向和切向磁场与环磁体周围的气隙。径向场分量激发A1262平面霍尔元件，并显示为Z方向。垂直霍尔元件响应切向磁场;这显示为y方向。与壳体1个环磁体一样，两个通道中的每一个的磁峰的位置相对于另一个通道非常一致。气隙几乎没有变化。图11更清楚地示出了仅显示最小和最大空气间隙，1.5和5.0mm的结果。

图9：径向B场直径磁磁磁体与气隙

图10：切向B场直径环磁体与气隙

图11.: Radial / Tangential B-Field Diametral Ring Magnet vs. Air Gap

图12和图13示出了两个传感器输出的磁力开关行为与单杆对环磁体。鉴于A1262的磁性开关点的正常变化以及气隙的大变化，外部和外部的相位关系仍然非常稳定。

图12：A1262多极环形磁铁外部（径向）与气隙

图13：A1262多极环形磁铁OUTB（切线）与气隙

As shown in Table 2 below, both outputs also maintain near-ideal (≈50%) duty cycle independent of air gap.

Table 2: Duty Cycle vs. Air Gap for Case 2

Air Gap (mm)	OUTA Duty Cycle (%)	OUTB Duty Cycle (%)
1.5	50.34	48.86
2.0	50.34	48.72
2.5	50.34	48.72
3.0	50.27	48.65
3.5	50.07	48.65
4.0	50.27	48.32
4.5	50.07	48.52
5.0	50.27	48.32

一贯占空比

表3中的数据示出了影响气隙和环形磁极 - 间距在外部和OUTB信号上的影响程度。

表3:工作周期比较

Ring Magnet	Air Gap	OUTA Duty Cycle (%)	OUTB Duty Cycle (%)
案例2.	闵。	50.34	48.86
	Max.	50.27	48.32
情况1	闵。	49.71.	49.83
	Max.	49.65	49.71.
平均占空比		49.99	49.18

这duty cycle of each signal varies by only a small amount over a 4:1 variation in pole-pitch and a >3:1 variation in air gap. The user is free to choose the ring magnet size based purely on mechanical considerations; the pole-pitch may be almost arbitrarily chosen to yield the desired number of cycles per revolution.

Phase Separation

这phase separation between the OUTA and OUTB signals will vary somewhat with changes in the air gap. This behavior is independent of the ring magnet configuration and is shown in Figure 14 and Figure 15, corresponding to the Case 1 and Case 2 magnets, respectively.

对于单极壳体2环磁体的多极壳体1环磁体的相移约4.0°（26.5° - 22.5°5°）和大约12°（102° - 90°）环磁体是由内部大厅的相互作用引起的元件间距，气隙和磁铁尺寸和材料。

总相移的大小（图14和图15）取决于磁极的数量。对于给定尺寸的环磁体的磁极数（较小的杆间距）的数量越大，信号相位的影响越少。

这phase separation of the OUTA and OUTB signals is generally slightly larger than 90°, because the vertical and planar Hall elements inside the A1262 are not located in exactly the same position on the silicon die.

该信号相位与气隙关系意味着相位可以用作系统气隙的指示。例如，可以使用它来确认气隙在系统的设计限制内。

This “air-gap signal” can be derived by measuring the time between the falling edges of OUTA and OUTB at a constant speed of magnet rotation. The measured time indicates the air gap distance and will increase if the air gap becomes larger.

图14.: Phase Shift Difference Between Two Falling Edges at the Multipole Ring Magnet Over Air Gap

图15.: Phase Shift Difference Between Two Falling Edges at the Diametral Magnet Over Air Gap

观察/结论

如上所示，A1262的传统平面和垂直霍尔传感器的独特配置具有以下优点：

• 这A1262 is capable of generating quadrature output signals (≈90° phase difference) where the phase separation is largely independent of the air gap, ring magnet size, or pole spacing.
• 这system designer has an unprecedented level of flexibility in selecting the ring magnet and its position and orientation relative to the sensor.
• 这user is very likely to be able to choose a standard, off-the-shelf ring magnet, selected to provide the desired number of pulses/revolution.
• 这limiting factor at larger air gaps is likely to be the tangential field strength (X or Y in the cases shown here), as the tangential field strength is generally lower than the radial field strength.
• OUTA和OUTB信号的相位关系可以用作气隙的指示。

Test Circuit

上述案例研究的应用电路是A1262数据表中所示的典型应用电路，并在下面的图16中再现。

图16：典型的应用电路

Ring Magnet Source

在箱1和案例2中使用的环形磁铁可从以下供应商，Allegro和Sanken半导体的分销商提供：

Matronic GmbH & Co.
电子Vertriebs kg.
Vor dem Kreuzberg 29
D-72070Tübingen，德国

Phone: +49 7071 94440
FAX +49 7071 45943
Web:www.matronic.com
Email:info@matronic.de

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