Fully Integrated Hall-Effect Motor Driver for Brushless DC Vibration Motor Applications
Fully Integrated Hall-Effect Motor Driver for Brushless DC Vibration Motor Applications
By Shaun Milano, Allegro MicroSystems, LLC
Abstract
Vibration motors are used in a variety of applications including mobile phone handsets, game joysticks, handheld video games, pagers, toothbrushes, and razors to name just a few. Of particular interest is the mobile handset market, as global production volume is expected to be greater than 1 billion handsets in 2007. The handset market has driven innovation in the design and manufacturing techniques of miniature vibration motors. Smaller handsets demand motors that consume less PCB area, and require a thin motor design. Motor features for caller ID vibration tones, and gaming applications are also being added to handsets. This paper will discuss an advanced Hall-effect technology Allegro™ MicroSystemsA1442brushless direct current BLDC motor driver ideally suited to deliver advanced handset vibration motor functionality.
Vibration Motor Designs
Most vibration motors consist of a small electrical motor that drives an unbalanced weight, as shown in figure1.
Figure 1. Coin-type vibration motor. A relatively flat eccentric weight spins in a protective enclosure. (1) enclosure, (2) rotor base, (3) weight, and (4) shaft.
电机是直流（DC）刷或无刷电机，并配置为两个基本品种：coin(orflat) andcylinder(orbar).
Cylinder type motors are simple brush motors with a traditional axial design, as shown in figure 2. Cylinder motors are employed in a variety of applications but are undesirable in mobile handset applications due to their large size. The cylinder type motor demands the most volume within the handset, and often the largest diameter space of all vibration motors.
图2.气缸（条）型振动电机，外部重量旋转垂直于身体。
所有刷子电机在换向点产生火花，因为画笔在电机线圈中切换电流。这些火花是宽带射频干扰（RFI）的优异发射机。刷子磨损并被证明是电机故障的主要原因。
需要更小的，更薄的设计导致刷电机技术的适配到硬币型电机中，如图3所示。与刷子接触的换向器点激励转子中的电线箱。激励线圈建立足够强的磁场，以与集成在定子中的环形磁铁相互作用，导致旋转。
如图3所示，换向点以交替的极性对排列，因此随着转子移动，线圈在通过换向点时恒定地扭转极性。以这种方式，电动机不断旋转，并且以与施加的电压成比例的速度。硬币设计中的更复杂的刷子通常不如其等效刷缸电机可靠。
图3.。Brush coin-type vibration motor exploded view. (1) enclosure top, (2) rotor (view as mounted), (3) rotor (inverted view), (4) enclosure bottom, (5) coils, (6) commutation points, (7) alternating power supply circuits, (8) ring magnet (showing representative polar zones), (9) power supply brushes.
Brushless Vibration Motors
As discussed, brushless motors bring extended motor life and eliminate RFI by their lack of sparks. BLDC designs are also providing the smallest diameter and thinnest coin-type motors in the industry. Figure 4 illustrates the basic construction of such a motor.
图4.。Brushless coin-type vibration motor exploded view. Brushes and commutation contacts are replaced by a Hall effect sensor IC (Allegro MicroSystems A1442 shown), and coils are relocated to the stator. (1) enclosure top, (2) rotor (view as mounted), (3) rotor (inverted view), (4) enclosure bottom, (5) ring magnet (showing representative polar zones), (6) eccentric weight, (7) coils.
我n this design, the rotor assembly includes the magnet as well as the weight that provides the vibration during rotation. The relatively bulky coils are moved to the stator, where they are connected to the controlling IC.
数字换向和线性软切换消除了火花，因此RFI干扰。完全集成的A1442霍尔效应装置和精密放大器耦合到通过比较器电路输出的内部全桥，确定正确的换向点。图4的电机中所示的第三丝是可选的，连接到A1442上的使能引脚，可用于控制主动制动和睡眠功能。可以通过将IC引脚绑定到PCB上的VCC来消除该第三线。
The A1442 is the only IC necessary to drive the motor. The functional block diagram in figure 5 illustrates the device operation and advanced features. Notice in figures 4 and 5 that the integrated Hall element eliminates the need for an external Hall element, and thereby reduces the motor PCB component count to just the A1442. The only external component required is a standard circuit feature, a 0.1 µF bypass capacitor located on the application motor mount PCB, used to minimize voltage spikes on the supply that are generated when switching an inductive load.
图5。A1442 BLDC vibration motor driver functional block diagram.
Soft-Switching and Commutation
当器件为向上电时，它会感应磁场并激活桥接器。根据磁极设置有源晶体管。南极性磁场激活输出晶体管Q1和Q4，驱动V的电流OUT1to VOUT2。As a north polarity magnetic pole approaches (due to rotation), Q1 and Q4 are turned off and Q2 and Q3 are turned on. This drives current from VOUT2to VOUT1从而反转在线圈中流动的电流方向。
电机设计变化，但最大RPM范围为9 000至15 000 rpm。大多数设计采用4极转子磁铁，使用6极磁铁的一些设计。使用这些参数，很容易计算换向频率（F.CS.，Hz）使用以下公式：
fCS.= RPM × PP / 60 ,
where PP is the quantity of pole-pairs. For a 4-pole magnet at 9 000 rpm, fCS.is 300 Hz, and for a 6-pole magnet at 15 000 rpm, it is 750 Hz. Thus, the commutation signal and coil current switching events occur in the audible frequency range. The soft-switching drive algorithm is optimum for minimizing the audible noise and EMI produced by switching the inductive motor coil load by gradually reducing and then reversing current in the coils. The timing diagram in figure 6 illustrates the switching behavior.
图6. A1442 BLDC振动电机驱动器时序图。（1）由A1442，（2）霍尔电路内部信号感测的转子磁体场，用于换向，（3）全桥接信号，（4）A1442输出，（5）诱导电机线圈电流。
Active Braking, Sleep Mode, and Anti-Stall
The Allegro A1442 has an integrated active braking function that can be used for fast stop-start cycling. Fast stop-start cycles are useful in mobile handsets for vibration ring tones, caller ID when the phone is in silent mode, and for gaming applications. The braking function is activated using the /SLEEP pin, shown in figure 5.
当向/睡眠引脚施加低信号时，A1442通过反转输出桥的极性并通过电动机线圈启动主动制动功能。反转电流和因此该领域的效果是施加力以沿反向旋转电动机，这将迅速减速电动机。制动后，A1442通过关闭IC的有源电路来进入睡眠模式。
During sleep mode, the current consumption of the IC is typically less than 1 µA. The /SLEEP pin can eliminate a FET transistor on the customer PCB that would otherwise be necessary to switch power to the motor on and off; as a result, the motor can be permanently connected to the battery.
如果电机档位，A1442将启动防失速算法。发生失速事件时，输出将不断打开和关闭以重新启动电机。开关周期产生扭矩循环，摇动电机并提高开始的概率。它还防止了可能损坏电机线圈的连续失速电流。
Protection and Ultra Thin Packaging
反向电池保护融合在A1442上以保护装置，以防电动机导线在PCB上无意中焊接，使返工成为可能。
我f the outputs of the coil are inadvertently shorted when the device is powered-on, the A1442 has thermal shutdown protection that will disable the outputs as the IC heats up. The reverse battery protection feature and thermal shutdown have proven to be very robust features for assembly plants and for rework at OEM board assembly.
With the advent of very thin designs, such as the Motorola®MOTORAZRTM值电话，振动电机的厚度已成为一个重要的销售功能。Allegro A1442设备可在世界上最薄的MLP包中提供。随着现成的电动机厚度趋向于1.5 mm，下方，使用Allegro EW包装，MLP（DFN）的额外设计灵活性，总封装高度为0.4 mm，长度和宽度尺寸仅为1.5 mm×2.0 mm。A1442 EW包如图7所示。
图7。A1442在电子战包中。
Summary
The A1442 is a full-bridge motor driver designed to drive low-voltage, brushless DC (BLDC) motors. Commutation of the motor is achieved by use of a single Hall element to detect the rotational position of an alternating-pole ring magnet. The device integrates all the necessary electronics. This includes the Hall element circuit used for commutation, the motor control circuitry, and the full output bridge.
This fully integrated single chip solution provides enhanced reliability (including reverse battery protection and output short circuit protection) and eliminates the need for any external support components besides the standard external 0.1 µF bypass capacitor.
The A1442 employs a soft-switching algorithm to minimize audible switching noise, and RFI and EMI interference. An active braking function is available on a third pin that can be used for fast stop-start cycles for caller ID and gaming functions. The third pin also enables a micropower sleep mode to reduce current consumption for battery management in portable electronic devices. The small footprint and low profile EW package enables extremely thin motor designs.
The Allegro A1442 BLDC motor driver is ideally suited to deliver advanced features and packaging in vibration motor applications in portable handsets and other products such as pagers, handheld video game controllers, electronic toothbrushes, and razors.