Micro-Power Position Sensing in Cell Phone Applications

By Shaun Milano, Allegro MicroSystems, LLC

Figure 1. The A1171 package is a maximum 0.4 mm in overall height, ideal for thin phone designs.

随着手机制造商开始集成铁道部e features into their models, the need for different mechanical configurations continues to expand. Micro-power Hall-effect sensor ICs are well suited for sensing the open-close slide positions given any phone configuration and are the most popular solution employed today in the market. Multipurpose phones often require sensing not only open-close, but also a third position, such as rotation, or flip-up in another direction. This note will show how to use the Allegro™A1171in a standard flip or slide phone, as well as techniques for sensing three positions using only one magnet and one Hall device in a multipurpose application.

标准滑盖或翻盖手机配置

In a standard configuration, a single Hall-effect IC and button magnet can be used to sense the open and closed positions.

In the closed position, the Hall IC, for example H as shown in figure 2A, is aligned with a simple button magnet, marked with its north (N) and south (S) poles. In this position, the Hall sensor IC output is latched in the on state, because the magnetic flux density is larger than the magnetic operate point of the device. In the open position (figure 2B), however, the magnetic field is sufficiently weak that the Hall sensor IC output is off. This simple technique is widely employed in both slide and flip phones.

使用全极IC开关可以简化制造，因为可以插入磁铁，而不必考虑哪个磁极朝向霍尔传感器IC。可以使用北极或南极来激活IC开关。在图2的例子中，南极是激活极，因为它被放置在离霍尔传感器IC最近的地方，但是对于全极传感器IC来说，将北极放置在那一边同样有效。

图2。霍尔效应传感器IC和磁铁的位置在一个标准的滑动电话。

图3和图4比较了全极开关（图3）和众所周知的单极开关（图4）的传递函数。在这两幅图中，垂直轴是IC对冲击磁场的输出电压响应。沿水平轴，显示了增加的北极磁通量（增加B-）、增加的南极磁通量（增加B+）和中性磁通量（B=0）。

图3. Transfer functions illustrating the effect of changes in the impinging magnetic field on output voltage for omnipolar Hall-effect IC switches: (A) effect on a low-flux–activated switch, and (B) effect on a high-flux–activated switch.

图4。单极霍尔效应集成电路开关的传递函数：（A）磁通量对北极激活开关的影响，以及（B）对南极激活开关的影响。

双模IC开关

Figure 5 shows a simple block diagram of the A1171 dual-mode switch. The term dual-mode refers to the A1171 capability of operating either as an omnipolar switch or as a pair of unipolar switches. The A1171 works at battery voltages as low as 1.65 V, allowing its use in phones and PDAs with the latest single-cell Lithium batteries. It also has push-pull outputs to eliminate the need for external pull-up resistors.

Figure 5. Functional block diagram of the Allegro A1171 omnipolar IC switch.

选择引脚的状态决定A1171的操作模式。当引脚浮动或绑定到VCC时，部件在全极模式下工作，如图3所示。当引脚接地时，A1171在单极模式下工作，如图4所示。注意，在全极模式（图3）中，单独的输出是互补的，而在单极模式（图4）中，单独的输出是南极或北极激活的开关。

通过在单极模式下使用两个输出，并调整感应磁铁的方向，A1171可用于感应三个位置，支持多用途电话应用所需的更广泛的铰接位置。在单极模式下，VOUTPS引脚是南极激活开关的输出，而VOUTPN引脚是北极激活开关的输出。亚博尊贵会员

多用途多位置应用亚博尊贵会员

多用途应用如图6所示。当手机完全关闭时（图6A），例如在MP3应用中，磁铁的南极与霍尔传感器IC相对。A1171的输出为VOUTPS low和VOUTPN high，对应于图4A和4B的B+侧。亚博尊贵会员

在滑开位置，用于电话应用（图6B），霍尔传感器IC由一个北极磁场控制，VOUTPN低，而VOUTPS高，对应于图4A和4B的B侧。最后，在旋转打开位置，用于在全键盘上使用文本或PDA（图6C），两个开关都不受限制一个有效的磁场，两个输出都很高（图4A和4B中的B=0）。

Figure 6. Multipurpose application for sliding and rotating phones.

输出真值表总结了所有三个电话位置和结果输出状态。这种技术可以应用于旋转或滑动手机，如果机械布局和感应磁铁进行了优化。

输出真值表
Application	MP3	电话	PDA/Texting
Position	Fully Closed	滑开	旋转打开
VOUTPS	L	H	H
VOUTPN	H	L	H

摘要

This note has described how to use an advanced Hall-effect sensor IC, the Allegro A1171, to sense two separate positions in omnipolar operating mode, and to sense three positions by enabling unipolar operation. These ICs allow improvements in manufacturing cost and application footprint, because three positions can be sensed using only one magnet and one Hall device. Guidance was also provided on using one of the omnipolar outputs or both of the unipolar outputs of the IC: VOUTPS and VOUTPN, as well as selecting the operating mode by using the SELECT input. The A1171 is ideally suited for position sensing in simple slide or flip phones as well as in three-position sensing for multipurpose slide or rotating applications.

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