Micro-Power Position Sensing in Cell Phone Applications
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.
标准幻灯片或翻盖电话配置
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OmniPolar IC开关促进了易于制造，因为可以插入磁体而不担心哪个杆面向霍尔传感器IC-北极或南极可用于激活IC开关。在图2示例中，南极是启动杆，因为它位于霍尔传感器IC最近的位置，但是用全方位的传感器IC，将北极放置在那侧的同样也可以很好地工作。
图2.标准幻灯片手机上的霍尔效应传感器IC和磁铁位置。
图3和4将OmniPolar开关（图3）的传递函数与众所周知的单极开关进行比较（图4）。在两个图中，垂直轴是IC的输出电压响应到撞击磁场。沿着水平轴，增加北极磁通量（增加B +），增加南极性磁通量（增加B +）和中性极性（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IC开关的传递函数：（a）北极激活开关上的磁通量效果，（b）在南极性激活开关上。
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.
选择引脚的状态确定A1171的操作模式。当引脚浮动或绑定到VCC时，该部件以全日生模式运行，如图3所示。当引脚接地时，A1171以单极模式操作，如图4所示单独的输出是互补的，而在单极模式下（图4）单独的输出是南方或北极启动开关。
通过使用单极模式下的输出，并定向感测磁体，A1171可用于感测三个位置，支持多用途电话应用中所需的铰接位置范围的更宽范围。亚博尊贵会员在单极模式下，VOUTP引脚是南极性激活开关的输出，VOUTPN引脚是北极激活开关的输出。
多用途多位置应用亚博尊贵会员
图6中示出了多用途应用程序。当电话完全关闭时（图6A），例如MP3应用中，磁铁的南极与霍尔传感器IC相对。亚博尊贵会员A1171的输出是Voutps低和Voutpn高，对应于图4a和4b的B +侧。
在用于手机应用的滑动打开位置（图6b），霍尔传感器IC由北极性场主导，Voutpn低，而Voutps高，对应于图4a和4b的b侧。最后，在旋转打开位置，用于在全键盘上发短信或PDA（图6c），两个开关都经受显着的磁场，并且两个输出都是高（图4a和4b中的b = 0）。
Figure 6. Multipurpose application for sliding and rotating phones.
输出真理表总结了所有三个电话位置和生成的输出状态。如果机械放置和感测磁体被优化，则该技术可以应用于旋转或滑动电话。
| 产出真理表 | |||
|---|---|---|---|
| Application | MP3 | 电话 | PDA/Texting |
| Position | Fully Closed | 幻灯片打开 | 旋转开放 |
| VOUTPS | L | H | H |
| VOUTPN | H | L | H |
概括
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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