Application Information
Fully Integrated Hall Effect Motor Driver
for Brushless DC Vibration Motor Applications
By Shaun Milano
Allegro MicroSystems, Inc.
Vibration motors are used in a variety of applications
including mobile phone handsets, game joysticks, handheld
video games, game system interface controllers, pagers,
toothbrushes, and razors to name just a few. Of particular
interest is the mobile handset market, which continues to
grow rapidly. Global production volume is expected to
be greater than 1 billion handsets in 2007. The handset
market has recently driven innovation in the design and
manufacturing techniques of miniature vibration motors.
Smaller handsets demand motors that consume less PCB
area, and the trend to thin phone designs 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® MicroSystems A1442 brushless 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 figure 1. The
motors are direct current (DC) brush or brushless motors,
and are configured in two basic varieties: coin (or flat) and
cylinder (or bar).
Cylinder type motors are simple brush motors with a
traditional axial design, as shown in figure 2. The eccentric
movement of the weight attached to the rotor provides
vibration during operation. The amount of vibration is
directly proportional to the voltage applied to the motor.
Cylinder motors are manufactured in high volumes and
are fairly inexpensive. Cylinder motors are employed in a
variety of applications but they are undesirable in mobile
handset applications for several reasons. The cylinder type
motor demands the most volume within the handset, and
often the largest diameter space of all vibration motors,
when we take into account the eccentric path of the weight
and clearances to adjacent unprotected components.
All brush motors create sparks at the commutation points,
as the brushes connect and disconnect the power supply to
the motor coils. Those familiar with radio history will know
that the first radio transmitters were spark-gap transmitters,
so these sparks are excellent transmitters of broadband radio
frequency interference (RFI). In addition, because brushes
wear out (proving to be the major cause of motor failure)
they make brush-type motors not as reliable as brushless
Enclosure
Rotor base
Weight
Shaft
Figure 1. Coin-type vibration motor. A relatively flat eccentric weight spins in a
protective enclosure.
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motors. The long length and the relatively large volume envelope
of the cylinder motor, combined with the fact that a brush motor
creates RFI and has limited lifetime, make it the least desirable
solution for mobile handsets.
The need for smaller, thinner designs led to the adaptation of
brush motor technology into the coin-type motor. Coin type
motors have a unique and simple design, like that shown in
figure 3. The commutator points that are in contact with the
brushes energize the electrical coils in the rotor. Energizing
the coils establishes a magnetic field strong enough to interact
with the ring magnet integrated into the stator. The crossing of
opposite polarity magnetic fields, between the stator magnet and
Figure 2. Cylinder (bar) type vibration motor. Traditional design, with
coils wrapped around the rotor shaft, and an external weight spinning
perpendicular to the body.
the rotor coils, drive the rotor so it moves to a position where the
magnetic interference is minimized.
As the rotor moves, the brushes break contact with the set of
commutator points that initially energized them, and the rotor
momentum carries the brushes in rotation until they make contact
with the next set of commutation points. As shown in figure 3,
the commutation points are arranged in alternating polarity pairs,
so as the rotor moves, the coils are constantly reversing polarity
as they pass over commutation points.
The motors are designed so that the magnetic poles in the ring
magnet are at the same angular displacement as the commutation
points, but opposite in polarity. As a result, when the coils change
polarity the magnetic field that they establish also reverses,
causing a new cross-polarity with the ring magnet, and thereby
driving the rotor to continue its motion around the shaft. In
this way the motor continually rotates, and at a speed that is
proportional to the applied voltage.
Although brush-type coin motors are innovative in comparison to
brush-type cylinder motors, they have relatively larger diameter
and thickness because the coils are integrated into the rotor. This
increases the total rotor mass required to generate vibration and
requires a corresponding increment in energy to drive it. Along
with similar concerns about brush lifetime, brush-type coin
Enclosure
Top
Commutation points
Rotor
(inverted view)
Alternating power
supply circuits
Ring magnet (showing
representative polar zones)
Rotor (view
as mounted)
Power supply brushes
Coils
Enclosure
Bottom
Figure 3. Brush coin-type vibration motor exploded view. Adaptation of brush technology to this new configuration did
not achieve the anticipated reduction in volume or increase in reliability.
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Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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motors as a result are generally less reliable than equivalent brush
cylinder motors.
Brushless Vibration Motors
As discussed in previous sections, brushless motors bring
extended motor life and eliminate RFI by their lack of sparks. But
these are only two of the advantages of brushless DC (BLDC)
motors. BLDC designs are providing the smallest diameter and
thinnest coin-type motors in the industry. Figure 4 illustrates the
basic construction of such a motor.
In this design, the rotor assembly includes the magnet as well as
the weight that provides the vibration during rotation. The weight
itself is reduced relative to the brush-type motor weight, and it
can be designed to occupy only the periphery of the rotor orbit
for maximum effect with minimum mass. The relatively bulky
coils are moved to the stator, where they are connected to the
controlling IC, and can be hard-wired to the power supply traces,
eliminating sparking and RFI generation.
Commutation is performed digitally by the switching IC, in this
case, the Allegro MicroSystems A1442. The fully integrated Hall
effect sensor and precision amplifier are coupled to an internal
full bridge output. Additionally, internal comparator circuits
determine the proper motor commutation points and initiate
proper coil commutation. The third wire shown in the motor of
figure 4 is optional, connecting to an enable pin on the A1442
that can be used to control the active braking and sleep functions.
This third wire can be eliminated and the IC pin tied to VCC on
the PCB, if the active braking function is not required.
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 itself. 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.
Ring magnet (showing
representative polar zones)
Enclosure
Top
Rotor
(inverted view)
Eccentric weight
Rotor (view
as mounted)
Coils
A1442
Enclosure
Bottom
Figure 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.
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Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
3
and Q4 are activated, driving current from VOUT1 to 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 VOUT2 to VOUT1, thereby reversing the direction
of current flowing in the coils. As the rotor spins, the passing
magnetic poles are sensed by the A1442 Hall element circuitry,
which continually reverses the direction of current flowing
in the coils.
Soft-Switching and Commutation
The integrated Hall element and amplifier provide the
commutation signal that controls the soft-switching drive logic
for the full-bridge output structure. When the device powers-up,
it senses the magnetic field and activates the bridge. The active
transistors are set according to the magnetic pole in order to spin
the motor in the proper direction. For example, when the A1442
senses a south polarity magnetic field, the output transistors Q1
VDD
Output
Full Bridge
Reverse Battery
SLEEP
0.1 μF
Power and Sleep
Mode Control
Active Braking
Control
Stall Detection
Hall
Element
Q1
Q3
Drive Logic
and
Soft Start
Control
VOUT1
VOUT2
Q2
Amp
M
Q4
Thermal Shutdown
Protection
GND
Figure 5. A1442 BLDC vibration motor driver functional block diagram
Rotor magnet field sensed by A1442
(South)
B
0
(North)
Hall circuitry internal signal for commutation
VPROC
Full bridge activation signals
VQ1,VQ4
VQ2,VQ3
A1442 output
VOUT1
VOUT2
Induced Motor Coil Current
I
0
t
Figure 6. A1442 BLDC vibration motor driver timing diagram
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Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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Motor designs vary, but maximum rpm ranges from 9000 to
15000 rpm. Most designs employ a 4-pole rotor magnet, with
a few designs using 6-pole magnets. Using these parameters,
it is easy to calculate the commutation switching frequency
(fCS , Hz) using the following formula:
fCS = RPM × PP / 60 ,
diagram in figure 6 illustrates the switching behavior. Mobile
handset applications require low audible noise, and low
RFI and EMI. The A1442 BLDC motor driver with linear
soft-switching makes it ideal for use in mobile handset
applications.
Active Braking, Sleep Mode, and Anti-Stall
where PP is the quantity of pole-pairs (combinations of
adjacent north and south poles; for example, a 4-pole
magnet has 2 pole-pairs). For a 4-pole magnet at 9000 rpm,
fCS is 300 Hz, and for a 6-pole magnet at 15000 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 produced by switching the inductive
motor coil load, as it minimizes motor stress by gradually
reducing and then reversing current in the coils. The timing
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
¯Ē
¯Ē
¯P̄¯ pin, shown in figure 5.
S̄L̄
¯Ē
¯Ē
¯P̄¯ pin, the A1442
When a low signal is applied to the S̄L̄
initiates the active braking function. This function operates
by reversing the polarity of the output bridge, thereby
reversing the current direction through the motor coils,
B
Stall Event
Restart
BOP
BRP
tRS
tRS
tRS
tRS
tRS
tRS
VOUT1
(Outputs
off)
(Outputs
off)
VOUT2
t
Figure 7. A1442 BLDC vibration motor driver anti-stall function timing diagram
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Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
5
which results in reversal of the magnetic fields generated by the
coils. The effect of reversing the fields is to apply force to rotate
the motor in the reverse direction, which will quickly decelerate
the motor. The A1442 actively brakes for a nominal period of
time and then enters sleep mode by shutting down the active
circuitry of the IC.
During sleep mode, the current consumption of the IC is
¯Ē
¯Ē
¯P̄¯ pin can eliminate a
typically less than 1 μA. Using the S̄L̄
FET transistor on the customer PCB that would otherwise be
¯Ē
¯Ē
¯P̄¯
necessary to switch power to the motor on and off. The S̄L̄
pin is very high impedance and can be driven with logic circuitry
that pulls the pin to ground to enable active braking, thereby
eliminating the need for the FET transistor. As a result, the motor
can be permanently connected to the battery.
If the motor stalls during startup or at any other time, the A1442
will initiate an anti-stall algorithm to restart the motor. The timing
diagram in figure 7 illustrates the operation of the feature. When
a stall event occurs, the outputs will be continually turned on and
off to restart the motor. This scheme has several advantages. The
on-off cycles generate torque cycles that shake the motor and
improve the probability of a start. It also prevents continuous stall
current that can damage the motor coils.
Protection and Ultra Thin Packaging
Reverse battery protection is incorporated onto the A1442 to
protect the device in case the motor wires are inadvertently
soldered backwards on the PCB. This makes it possible to rework
the PCB after testing without wasting the motor by having it fail
catastrophically from reverse battery damage.
During motor assembly, the outputs of the coil can be
inadvertently shorted when the device is powered-on during
tests performed before the motor enclosure top is attached. The
A1442 has thermal shutdown protection that will engage as the
IC heats up and will disable the outputs. 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®
MOTORAZR™ phone and many others, the thickness of the
vibration motor has become an important selling feature. The
Allegro A1442 device is available in one of the world’s thinnest
MLP packages. With present finished motor thickness trending
toward 1.5 mm and below, additional design flexibility is
obtainable using the Allegro EW package, an MLP (DFN) with
an overall package height of 0.4 mm maximum, and length and
width dimensions of only 1.5 mm × 2.0 mm. The A1442 EW
package is shown in figure 8.
Summary
The A1442 is a full-bridge motor driver designed to drive lowvoltage, brushless DC (BLDC) motors. Commutation of the
motor is achieved by use of a single Hall element sensor to detect
the rotational position of an alternating-pole ring magnet. The
device integrates all the necessary electronics. This includes the
Hall element sensor 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
Figure 8. A1442 in EW package
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Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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circuit protection) and eliminates the need for any external
support components besides the standard external 0.1 μF bypass
capacitor.
feature also allows the removal of a FET transistor for switching
the device on and off. The small footprint and low profile EW
package enables extremely thin motor designs.
The A1442 employs a soft-switching algorithm to reduce audible
switching noise, and RFI and EMI interference. An active braking
function is available on a third pin that can be used for fast stopstart 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. This
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.
Copyright ©2007, Allegro MicroSystems, Inc.
The products described herein are manufactured under one or more of the following U.S. patents: 5,045,920; 5,264,783; 5,442,283; 5,389,889;
5,581,179; 5,517,112; 5,619,137; 5,621,319; 5,650,719; 5,686,894; 5,694,038; 5,729,130; 5,917,320; and other patents pending.
Allegro MicroSystems, Inc. reserves the right to make, from time to time, such departures from the detail specifications as may be required to permit improvements in the performance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that the
information being relied upon is current.
Allegro’s products are not to be used in life support devices or systems, if a failure of an Allegro product can reasonably be expected to cause the
failure of that life support device or system, or to affect the safety or effectiveness of that device or system.
The information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, Inc. assumes no responsibility for its use;
nor for any infringement of patents or other rights of third parties which may result from its use.
For the latest version of this document, visit our website:
www.allegromicro.com
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Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
7