`
`I n n o v a t i o n s E m b e d d e dI n n o v a t i o n s E m b e d d e d
`
`Applications for
`Hall Effect IC Switches
`in Portable Applications
`
`ROHM MarketingUSA
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`White Paper
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`Presented by ROHM Semiconductor
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`APPLE 1057
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`

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`Applications for Hall Effect IC Switches
`in Portable Electronics
`
`19th century magnetic technology merged with 21st century ultra-small
`IC package innovation offers beneficial alternative to mechanical devices
`
`According to the Semiconductor Industry Association,
`consumer electronics became the largest user and
`primary driver of semiconductors in 2004 and contin-
`ues to increase over the corporate market segment. In
`consumer electronics, portable products are the fast-
`est growing area. With cell phones alone projected to
`grow from over a billion units in 2007 to almost 1.5 bil-
`lion in 2010 according to market research firm Gartner
`Dataquest, it should be no surprise.
`
`While providing high volume opportunites for suppli-
`ers of the right components, consumer electronics and
`especially the portable consumer electronics portion
`places high demand on suppliers, requiring small size,
`high functionality, low power consumption and low cost
`as the major criteria for acceptance. In this highly com-
`petitive arena, the Hall effect, a magnetic technology
`discovered in the 19th century and popularized in the
`latter part of the 20th century through its implementation
`using large-scale integrated circuit (LSI) technology and
`advanced packaging is proving to be the right solution
`for adding functionality to cellular phones, portable com-
`puters, digital cameras, navigation systems, electronic
`toys and more.
`
`In portable consumer electronic products, Hall effect
`sensors provide an effective alternative to mechanical
`switches with increased reliability as well as cost and/or
`performance advantages over other non-contact tech-
`nologies. Using integrated bipolar sensing and CMOS
`logic circuitry with highly reliable semiconductor packag-
`ing and a small magnet, the Hall integrated circuit (IC)
`provides several useful functions.
`
`Applications in Portable Electronics
`
`In consumer electronics, product acceptance is increas-
`ingly determined by:
`
`• the user interface, where sensors provide awareness
`• the overall user experience, where a subtle feature
`can become a wow factor.
`
`The use of Hall effect IC switches are contributing to
`product acceptance in several of these applications.
`
`Open/Close Detection
`
`Portable computers and flip or jack-knife style phones
`and other portable devices with a rotating hinge and
`clam shell design (see Figure 1) have historically used
`mechanical switches to indicate an open or closed posi-
`tion. Knowing whether the device is open or closed is
`essential for applying power to sleeping circuitry and
`returning to the sleep mode to conserve power.
`
`Figure 1. Hall IC switch detects presence of magnet when the phone
`cover is closed
`
`The Hall effect IC switch detects the presence or
`absence of a magnetic field and outputs a digital signal
`for ON/OFF. In contrast to a mechanical switch with
`its potential wear-out mechanism, the Hall approach
`is a non-contact, long-life solution. In many cases, the
`
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`ROHM Semiconductor
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`Hall Effect ICs in Portable Electronics
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`Hall effect switch can simplify the location of the sensor
`compared to a mechanical switch.
`
`Some newer cell phones, digital cameras and other
`portable instruments use a sliding mechanism (Figure 2)
`where linear motion reveals the display or even a key-
`board normally covered when the unit is in a standby
`mode. In this application, a Hall effect IC switch / mag-
`net combination is commonly used.
`
`Figure 2. Hall IC switch detects presence of magnet when the phone
`cover is closed
`
`In these applications, the use of a Unipolar Hall effect
`IC is commonly used. Unipolar Hall IC switches only
`operate when a magnetic field of sufficient strength and
`polarity is detected. S-pole detecting devices are most
`common but N-pole detecting devices are also available.
`
`Hall effect IC switches capable of detecting a magnetic
`field of either polarity (Omnipolar) can also be used in
`this application. The unipolar devices typically require
`less power to operate but require the magnet to oriented
`properly while the omnipolar devices will operate without
`regard to magnet orientation.
`
`Screen Orientation
`
`In another variation, the screen pivots allowing the front
`or back face of the display to be viewed and the sys-
`tem has to discern which side of the display is facing
`the viewer. This application is also commonly found on
`PDAs, digital cameras, or tablet-style PCs. There are
`even some flat panel displays for desktop computers
`can rotate to view a portrait versus a landscape mode.
`
`In these applications, it is necessary to use a Hall effect
`IC sensor, not only capable of detecting the magnetic
`field but also of discriminating the polarity of the field.
`(Figure 3)
`
`Omnipolar Hall effect IC switches equipped with dual
`outputs make it possible to control screen orientation
`and other similar functions with a single device.
`
`Function Selection and Control
`
`An increasingly important function in multi-function
`cell phones is the jog wheel or track ball (Figure 4), a
`human interface allowing the user to scroll through a list,
`increase or decrease the volume or implement another
`function. Some lower cost MP3 players use a jog wheel
`that moves clockwise or counterclockwise to select MP3
`songs or scroll through a list of menu items.
`
`Capacitive and even resistive touch sensing are also
`used for these applications, but the Hall effect sensor
`provides a lower cost solution.
`
`H
`L
`D
`
`3
`
`3D
`
`E
`F
`
`
`
`11
`
`C L R
`C L R
`
`2 A
`
`2
`
`B
`
`C
`
`5 J K L
`
`5
`
`
`
`44
`
`G
`
`H I
`
`7
`7
`
`P
`
`Q
`
`R S
`
`8
`
`8 T
`
`D
`
`E
`
`F
`
`S-pole
`magnet
`
`R o tate
`
`
`
`N-pole
`magnet
`
`HLD
`
`3
`3
`
`DEF
`
`A B C
`
`JK L
`
`4
`
`G
`
`H I
`
` Open
`
`The front face
`is recognized
`via S-pole
`detection
`
`6
`
`6M
`
`N
`O
`
`U
`
`V
`
`0
`0
`
`9W
`9
`
`X
`Y
`Z
`
`# @ / .
`
`#
`
`ose Open
`
`Cl
`
`
`
`11
`
`CLR
`
`
`
`22
`
`HLD
`
`4 GHI
`
`4
`
`3
`3
`
`6
`6
`
`9
`9
`
`
`
`##
`
`
`
`55
`
`7 PQRS
`
`7
`
`
`
`88
`
`
`
`00
`
`DEF
`
`The back face
`is recognized
`via N-pole
`detection
`
`6 M
`
`6
`
`N
`O
`
`T U V
`
`
`
`99W
`
`X
`Y
`Z
`
`
`
`e
`
`Clos
`
`Figure 3. Polarity-discriminating Omnipolar Hall effect IC switches can be used to control the operation and orientation of multiple displays
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`ROHM Semiconductor
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`Hall Effect ICs in Portable Electronics
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`Design considerations for the various Hall effect sensing
`applications include magnetic strength and proximity of
`the magnet. For the smallest sensing system, neodymi-
`um magnets are recommended over ferrite magnets. A
`4 x 4 mm neodymium magnet of 1 mm or 3 mm thick-
`ness operates with a separation of 7.66 mm to 10.4
`mm between the magnet and the Hall IC. Increasing the
`detection distance requires increasing the thickness,
`sectional area or both.
`
`For some cell phones, MR (magnetoresistive), GMR
`(giant magnetoresistive) or AMR (anisotropic magnetore-
`sistive) sensing has also been used. The field direction is
`opposite to the Hall effect, which requires an orthogonal
`magnetic field. In general, the magnet strength needs to
`be about twice as large as a Hall effect device. However,
`prior to the introduction of chip scale packaging for Hall
`effect sensors, the MR packaging was smaller. With
`newer, smaller Hall effect ICs such as ROHM’s products
`in the 1.1 x 1.1 x 0.5 mm chip scale package, the MR
`package size advantage has essentially disappeared
`especially since designers can save space and cost by
`using a smaller magnet.
`
`Figure 5. A Hall voltage results from current flow in the semiconductor
`material when a magnet is located perpendicular to the flow
`
`Figure 4. Bipolar Hall IC switches detect the presence of alternating
`polarity magnetic fields to discern CW or CCW movement
`
`This application requires the use of two Bipolar, latching
`Hall ICs. The jog wheel has a series of alternating n-pole
`and s-pole oriented magnets. The two Hall ICs operat-
`ing in combination are used to detect either clockwise or
`counterclockwise rotation of the wheel.
`
`In more advanced applications in phones, computers
`and game handsets use a track ball that moves up and
`down and right and left. The design uses four Hall effect
`switches to determine the direction and how fast the ball
`is moving.
`
`While mobile phones use Hall sensors for a variety of
`functions, some of these same applications can easily
`be found in portable computers, digital still cameras,
`digital video cameras, video game controllers, navigation
`systems, electronic toys and more.
`
`Hall Effect Technology Basics
`
`Current flowing in a conductor perpendicular to a mag-
`net field causes a voltage, known as the Hall voltage on
`opposite sides of the conductor. While this has been
`known since 1879 when Edwin Hall discovered the
`phenomena, semiconductor technology has reduced
`the size of the Hall effect devices and added several key
`features that make Hall effect switches, sensors, and
`other products extremely useful in many applications.
`As shown in Figure 5, a magnetic field perpendicular to
`the plane of the semiconductor package, and the chip
`inside it, causes a low level Hall voltage. The Hall ele-
`ment is configured as a Wheatstone bridge, requiring
`additional circuitry including amplification and offset volt-
`age compensation.
`
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`ROHM Semiconductor
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`Hall Effect ICs in Portable Electronics
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`ROHM Hall Effect Technology
`
`ROHM’s Hall ICs use a single monolithic silicon chip with
`built in circuitry to provide additional functions and ease
`of interfacing. Also, instead of an analog output that is
`always on, ROHM pioneered the use of CMOS logic at
`the output to provide low power consumption. Today,
`all ROHM Hall effect switches use CMOS push-pull logic
`to provide a digital output that eliminates the need for
`an external pull up resistor required for the single FET
`output common in other Hall effect switches. The CMOS
`output interfaces directly to microcontrollers. Figure 6
`shows the Hall effect element with the additional circuitry
`common to all ROHM Hall ICs that includes timing logic
`(SW), dynamic offset cancellation, amplification, sample
`and hold, comparator, oscillator, latch and the push-pull
`output. Some of ROHM’s Hall sensors have two push-
`pull outputs for even greater functionality
`
`Figure 6. The block diagram of ROHM Hall effect shows the additional
`circuitry integrated with the Hall sensor that makes it easy to
`interface in sensing applications.
`
`Sample and hold circuitry reduces power consump-
`tion for power conscious battery-powered applications.
`ROHM’s Hall ICs typically have a sampling period of 50
`milliseconds. As shown in Figure 7, the device wakes up
`for a 48 µs sample of the magnetic field and then returns
`to sleep. As a result, the typical operating current is only
`8 µA for 2.7V applications and an even lower 5 µA for
`1.8V operation. Since ROHM Hall ICs were designed
`for battery powered applications, they can operate from
`voltages as low as 1.65 to 3.3V.The bipolar Hall ICs
`
`Figure 7. The typical sample time of 48 µs for each 50 ms period reduc-
`es the average current draw to 8µA or even 5 µA.
`
`designed for jog wheel or track ball applications have a
`much faster sampling period (0.5 ms).
`
`The design of the sensing element and circuitry in
`ROHM Hall effect ICs ensures high electrostatic dis-
`charge (ESD) tolerance with ratings of up to 8 kV as
`measured in the human body model (HBM). Operating
`over a temperature range of -40°C to 85°C, the mono-
`lithic silicon Hall sensor has a high level of magnetic flux
`density detection stability versus temperature. In addi-
`tion, many models have a high sensitivity with typical
`operating point of 3.7 mT (3.0 mT on ICs designed for
`1.8V operation). Dynamic offset cancellation eliminates
`the differential in the Hall element Wheatstone bridge
`for improved accuracy and a hysteresis comparator
`increases the noise resistance.
`
`With a mounting area of 1.1 x 1.1 x 0.5 mm, ROHM’s
`VCSP5OL1 chip scale package (CSP) provides the
`smallest Hall effect sensor for the most demanding,
`space limited applications. The image below shows
`the CSP compared the HVSOF5 surface-mount (SMT)
`package.
`
`Figure 8. ROHM Hall ICs are offered in the surface-mount HVSOF5
`package with a footprint of just 1.6 x 1.6 mm and in the even
`smaller VCSP5OL1 1.1 mm square, chip scale package.
`
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`ROHM Semiconductor
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`Hall Effect ICs in Portable Electronics
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`ROHM Hall Effect Topologies
`
`To provide the right sensor for a variety of applications,
`ROHM Hall ICs are available in four different designs as
`shown in Figures 9a – 9d.
`
`Unipolar devices only detect the presence of a specific
`polarity magnetic field. Competing Hall IC vendors typi-
`cally offer this type of device for S-pole sensing only.
`
`Polarity Discriminating (Omnipolar) Hall sensors have
`dual outputs and discern N- and S-poles so position
`and orientation can be detected.
`
`Figure 9a. ROHM Unipolar Hall IC topology shown for S-Pole Detection
`
`ROHM offers both N-pole and S-pole versions. Unipolar
`devices offer the highest energy savings but require
`extra care in proper polarity placement of the magnet.
`
`Figure 9c. ROHM Polarrity-Discriminating Omnipolar Hall IC Switches
`have dual outputs
`
`Bipolar (latching) operation Hall devices detect alternat-
`ing poles but do not change state if a pole is not detect-
`ed. The newest bipolar design, the BU52040HFV, has
`a 0.5 ms response time, about 100 times faster than
`other ROHM Hall sensors, to meet the requirements
`of jog wheel applications on digital cameras, mobile
`phones, PDAs or MP3 players.
`
`Omnipolar Hall ICs detect both magnetic poles, eliminat-
`ing the need to mark the magnet’s surface.
`
`S to N
`
`N to S
`
`Hall
`Element
`
`Latch
`
`Output
`OUT
`High Low
`
`S-pole
`detected
`
`Output operation
`
`OUT
`
`S
`
`N
`
`VDD
`
`Timing
`Logic
`
`Magnetic
`Flux Density
`
`LH
`
`Dynamic
`Offset
`Cancel
`
`Amp
`
`Sample
`&
`Hold
`
`Comp
`
`GND
`
`S
`
`0
`
`N
`
`N-pole
`Detection
`
`Figure 9b. ROHM Omnipolar Hall IC topology detects either N or S-pole
`
`Figure 9d. ROHM Bipolar Hall IC changes state only when magnetic
`polarity is reversed
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`ROHM Semiconductor
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`Hall Effect ICs in Portable Electronics
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`Hall Effect in Future Products
`
`While portable consumer electronic products represent
`a rapidly growing market for Hall effect switches, it is
`just one segment which can benefit from the technol-
`ogy. Similar functions are frequently required in the
`white goods industry, especially for the door open/shut
`indication. Even automobiles can take advantage of the
`non-contacting sensing in applications such as steer-
`ing wheel position/rotation. While products for these
`applications must meet different specifications including
`higher voltage operation than consumer products, they
`are among the planned additions to ROHM’s product
`portfolio. Ultimately, several industries will benefit from
`the use of small but sensitive Hall effect ICs.
`
`Other ROHM Products in Portable
`Electronics
`
`In addition to Hall IC switches, ROHM has an exten-
`sive portfolio of products filling many of the “sockets”
`in portable electronics devices. For a complete view of
`ROHM’s product portfolio, application-by-application,
`visit
`http://www.rohm.com/products/application/index.html
`
`To get more details on the complete line of ROHM Hall
`effect IC switches, visit:
`www.rohmsemiconductor.com/Hall_ICs.html
`At this site you will find a comprehensive product selec-
`tion guide, product datasheets and additional application
`information.
`
`
`
`©2008 ROHM Semiconductor
`
`All rights reserved. Subject to change without notice
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`NOTE: For the most current product information, contact a ROHM sales representative in your area.
`ROHM assumes no responsibility for the use of any circuits described herein, conveys no license under any patent or other right, and
`makes no representations that the circuits are free from patent infringement. Specifications subject to change without notice for the purpose
`of improvement.
`The products listed in this catalog are designed to be used with ordinary electronic equipment or devices (such as audio visual equipment,
`office-automation equipment, communications devices, electrical appliances and electronic toys). Should you intend to use these products
`with equipment or devices which require an extremely high level of reliability and the malfunction of which would directly endanger human
`life (such as medical instruments, transportation equipment, aerospace machinery, nuclear-reactor controllers, fuel controllers and other
`safety devices), please be sure to consult with our sales representative in advance.
`© 2009 ROHM Semiconductor USA, LLC. Although every effort has been made to ensure accuracy, ROHM accepts no responsibility for
`errors or omissions. Specifications and product availability may be revised without notice. No part of this document represents an offer or
`contract. Industry part numbers, where specified, are given as an approximate comparative guide to circuit function only. Consult ROHM
`prior to use of components in safety, health or life-critical systems. All trademarks acknowledged.
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