domingo, 25 de julio de 2010

Allegro Hall Effect-Based Current Sensor ICs

Hall Effect Basics

Hall-Effect Sensor ICs:

Inherent Galvanic Isolation

High Power Applications:

Sensing > 200 A Currents with Allegro Sensor ICs

1 mm "thin"package for enhanced accuracy; placed in the gap of a ferromagnetic concentrator.

Allegro's high bandwidth current sensor SIP: the A136x family.

Sensing 50 to 200 A

Allegro's ACS75x Family of Devices

  • Small physical size (7 mm nominal height).

  • 100 ?Ω integrated conductor, galvanic isolation for line-powered systems.

  • Enhanced accuracy, typically < 4% total error from -40°C to 150°C.

  • Low noise, > 100 kHz bandwidth sensor.

  • Integrated shield reduces output spiking in high dV/dt applications.

  • Allegro's recently released the ACS756 and ACS758 devices include significant advances over previous generations.

    Sensing < 50 A

    Allegro's ACS712 Family of Flip-Chip Devices

  • SOIC8 with integrated 1.2 mΩ conductor.

  • Isolation for line powered applications.

  • <4% typical error over -40°C to 150°C range.

  • Low noise, 80 kHz bandwidth current sensor.

  • Integrated shield reduces output spiking in high dV/dt applications.

  • Flip chip assembly techniques locate the Hall transducer very close to the integrated conductor.

    High Bandwidth AC Sensing

    Allegro Shield Solution

  • A parasitic capacitor is formed by the current-carrying leadframe and the Hall-effect IC surface.

  • Adding an electrostatic shield between the silicon and the current-carrying leadframe allows the noise to bypass the silicon.

  • Shield layer is connected to device ground inside the package.

  • Allegro Product Line and Applications Overview

    A1360 Series


    • DC/DC Converters.
    • Inverters.
    • Battery Current Measurement.
    • Smart Metering.
    • Hybrid Vehicles.

    ACS712 Family 5 to 50 A


    • Industrial Motors.
    • Lighting.
    • Power Supplies.
    • White Goods.
    • Hybrid Vehicles.

    ACS756 & ACS758 50 to 200 A


    • UPS Systems.
    • HVAC Control.
    • Inverters.
    • Power Supplies.
    • Hybrid Vehicles.
    • Power Steering and Braking Systems.

    A growing portfolio with many new, unannounced products under development.!

    Nombre: Rodriguez B. Joiver I.
    Asignatura: CRF

    Vehicle Safety Systems

    Seat Position Sensing

    Figure 1. Front- and Side-Impact Air Bags Require Precise Data on the Location of the Seats and Occupants

    Occupant safety is one of the most critical elements of the automobile design. As a result, safety systems continue to become more sophisticated in order to limit, and ultimately prevent, personal injury in the case of an accident.

    Seat position sensing is used in safety systems to determine the position of an occupant in relation to the steering wheel, preventing the air bags from deploying with excessive force.

    The most common solution today incorporates two-wire, unipolar, Hall-effect switches in sensing discrete seat position zones. The sensor IC must relay this information in the form of a digital output to the controller unit indicating a particular zone. This information must be correct at start up of the vehicle, so the sensor IC output must decode without any user action.

    The seat track is typically a ferrous metal material capable of interrupting the magnetic field between the Hall-effect sensor IC and a magnet. The ferrous metal of the seat track passes between the switch and the magnet causing the switch to turn on or off, relaying seat position information to the controller unit. A change in the output state of the sensor IC indicates to the controller unit that the seat has passed into a particular zone.

    There can be any number of zones depending on how many Hall-effect sensor ICs are used, assuming two sensor ICs per seat track, four zones would be possible. The information, provided by the Hall sensor IC, is processed by the controller to determine the seat position relative to the steering wheel. A seat that is in one of the closer zones to the steering wheel would indicate to the controller unit that a lower force deployment is necessary. Seat positions that are in one of the rear zones, furthest from the steering wheel, require a higher force deployment. The controller unit decodes the output states of the Hall-effect sensor ICs to determine in which zone the seat is positioned. Two sensor ICs will provide a convenient Grey Code output as shown in figure 2 and the table below.

    Figure 2. Position Sensor ICs Relay Proper Seat Location to the Controller Unit the Entire Time the Vehicle is On

    Occupants are unaware of the fact that the vehicle is making life or death decisions automatically with no user interface required.

    The vast selection of Hall-effect sensor ICs allows different solutions for the same application. A higher resolution may be required to determine exactly where the seat is at all times. The highest resolution solution is to use a linear, analog Hall sensor IC, which produces a voltage output proportional to the strength of the magnetic field. A dual pole magnet in a slide-by configuration with the linear will produce an output ranging from 0 volts to 5 volts with the proper design.

    Hall-effect technology is highly reliable and relatively inexpensive. If automatic sensing is required the solution must be dependable.

    If higher precision is required, programmable switches and linear devices are available, and can minimize stack up tolerances by allowing end-of-line programming.
    Ferrous targets can be detected using a back-biased Hall-effect sensor IC. These sensor ICs incorporate a Hall circuit and rare-earth pellet in one overmolded assembly. Back-biased solutions are offered for switch and linear designs. These assemblies simplify manufacturing and offer an optimized electrical and magnetic design in a single overmolded package.

    Seat Belt Buckle Sensing

    The seat belt buckle, SBB, is another area where Hall-effect technology has been used as a part of the safety system. The two-wire, unipolar switch is again a simple, yet reliable, solution common to many automobiles on the road today. The purpose of the Hall-effect device (HED) is to guarantee proper latching of the buckle whereby ensuring the occupant is properly restrained in the event of an accident or sudden stop.

    Similar to the seat position sensing application, seat belt buckle switches operate using a vane interrupt concept. In this case the buckle, made of a ferrous material, is responsible for interrupting the magnetic field between a magnet and the Hall-effect device. Typically when the field is interrupted, the device output switches on and when the buckle is removed the device switches off. This information is sent to the controller, which then processes the data in conjunction with data from the seat position sensor IC and other outputs in order to reliably deploy air bags in the event of an accident.

    Application Hurdles

    • The SBB sensor IC has tight spatial constraints, making the use of a printed circuit board difficult. Therefore, welding the interconnect wires to the HED leads is the more common approach, as part of the packaging process, to minimize size. However, welding to the leads takes expertise in welding and is typically contracted out to a welding facility. One of the most common errors seen in welding Hall-effect devices is an excessive amount of heat/power allowed to reach the IC, causing wire bonds to be catastrophically damaged. Another common error seen in new welding processes is insufficient clamping of the leads, allowing the leads to twist or pull during the contact with the weld tip. This will also cause catastrophic damage to the wire bonds.
    • In addition to the spatial constraints, the sensor IC is subjected to high ESD levels and to magnetic interference due to:
      • customer-accessible points within the vehicle, such as the tongue of the buckle assembly,
      • shunting effects, on the magnetic field, to the sensor IC due to the ferrous properties of the buckle assembly, and
      • wide tolerances of the mechanical buckle assembly, causing large variations in the magnetic field impinging on the Hall-effect sensor IC.
    Choosing the right sensor IC is critical to meeting all the application requirements.

    Application Solutions

  • Transient/ESD protection has been accomplished with the use of a 0.1 µF bypass capacitor welded between sensor IC supply and sensor IC ground. In the case of a PCB, an MOV has been used in addition to the bypass capacitor to protect the sensor IC against harsh EMC/ESD conditions due to the use of a chassis ground. Just a bypass capacitor may be sufficient when the sensor IC is robust against EMC/ESD.

  • A sufficiently large magnet is required to overcome the shunting effect caused by the buckle assembly itself. SmCo and Neodymium are common magnet materials used in Seat Belt Buckle applications. They provide large field levels to compensate for the mechanical tolerances and possibly large air gaps >  3 mm) seen in SBB applications.

  • Tolerances of the mechanical assembly can cause a large gauss variation (hundreds of gauss) in the field level impinging on the sensor IC; so all conditions must be characterized to ensure the sensor IC never switches into the incorrect state. The conditions that must not cause false switching of the Hall-effect sensor IC are as follows:
    • Normal buckled position with the tongue in place.
    • Normal unbuckled position with the tongue removed.
    • Over-travel of the tongue when pushed in and held by a person sitting on it, or by a child seat resting on the buckle assembly.
    • False latch condition when something other than the actual tongue is pushed in, holding the buckle in a falsely latched condition (popsicle stick, toy, etc).

  • Figure 3. Typical Mechanical Assembly of Seat Belt Buckle.

    Showing electrical connection to Hall-effect sensor IC.

    Nombre: Rodriguez B. Joiver I.
    Asignatura: CRF

    Recent Trends in Hall Effect Current Sensing


    The demand for low-cost, accurate, small-size current sensor solutions has grown rapidly during the last decade, in industrial, automotive, commercial, and communications systems. Various technologies can be used to transduce an electric current to a proportional voltage. The advantages of a Hall-effect magnetic detector are the inherent voltage isolation from the current path and the integration of the Hall element and interface electronics on a single silicon chip.[1] New design concepts and the systematic use of advanced BiCMOS technology have allowed further improvements in IC performance. These also have opened the door to new product approaches by supporting the integration of additional functions, such as power protection, in the same current sensor IC. This paper covers the basic packaging and IC design concepts of the Allegro® ACS current sensor IC family and explores some recent trends that have enabled Allegro to develop its next generation of fully integrated low-cost current sensor devices.

    Packaging Concept

    Allegro current sensor IC devices are characterized by the integration of a monolithic linear Hall IC and a low-resistance primary current conduction path into a single-shot overmolded package.[2] Device accuracy is optimized through the close proximity and precise positioning of the Hall transducer relative to the copper conductor. Low power losses and high voltage isolation are intrinsic to the packaging concept. The final size, shape, and additional components of the packaged current measurement systems depend on the amplitude of primary current to be measured. This sections details the innovative packaging technologies for different current measurement ranges.

    Currents up to 20 A

    For small nominal currents, up to ±20 A, the Hall die and the primary current path are packaged in a standard-footprint SOIC8 surface mount package, shown in figure 1 and figure 3. This provides a compact, low profile solution that is compatible with high volume automated board assembly techniques. The use of flip-chip technology allows an optimized magnetic coupling between the active face of the Hall element and the magnetic field generated by the current being sensed. A flux concentrator is therefore not required. The internal resistance of the copper path used for current sensing is typically 1.5 mΩ for low power loss. The power terminals are also electrically isolated from the low voltage signal I/O pins. Careful IC and package design permitted further improvement of the voltage isolation of the device, with a typical DC isolation voltage of 5 kV, and an rms isolation voltage of 1.6 kV minimum and 2.5 kV typical (at 60 Hz for 1 minute) between primary current path and signal sides.

    Figure 1. Internal Structure of an ACS Package

    Showing the U-shaped primary copper conductor and the single flip-chip–mounted Hall IC.

    Figure 2. Internal Structure of the CB Package

    Showing the primary conductor (copper, left), the flux concentrator (red) and the linear sip Hall ic (black) and signal pins (copper, right).

    Figure 3. Photograph of ±20 A (LC Package) and ±200 A (CB Package) Current Sensor ICs

    Shown with a coin for comparison.

    Currents up to 200 A

    For higher currents, the cross section of the copper conductor has to be increased to accommodate the current density within the material, which is provided in the CB package. Because of the magnetic coupling between this thicker conductor and the linear Hall element, a flux concentrator has to be used. The copper path, linear SIP Hall device, and concentrator are precisely assembled before being overmolded. Through careful design of the system, the primary conductor resistance is typically as low as 100 µΩ and a minimum rms isolation voltage of 3 kV (at 60 Hz for 1 minute) is achieved between primary path and signal sides. Figure 2 shows the internal structure of such a ±200 A current sensor, and figure 3 shows a photograph of both this and the ±20 A package types.

    Currents Above 200 A

    If currents to be measured are higher than 200 A, the ICs can be used in a current divider configuration.[3] This method involves splitting the path of the current being sensed. The simplest approach is to design a notched bus bar such that only a well-controlled fraction of the current flows through the device, the other going through a shunt path (see figure 4). The current split ratio is determined by the geometry of the bus bar. An inherent disadvantage of this approach is that it reduces the current resolution by the same proportion as the current is divided.

    The resolution of the current sensing system can be increased if the current is split equally and two devices are used in parallel (see figure 5). A simple circuit involving level-shifting and adding the outputs of the two devices can be used to obtain a linear output proportional to the total primary current.[3]

    Figure 4. Current Divider Configuration

    The current sensor IC can be connected directly to a bus bar.

    Figure 5. Equal Current Splitting with Enhanced Resolution

    The outputs of the two devices can be combined to obtain a linear output proportional to the total current to be sensed.

    IC Design

    This section details the basic chip architecture and most important IC parameters.

    Block Diagram The central element of the device is a precise, low-offset silicon Hall IC. A block diagram is shown in figure 6. The magnetic flux generated by the primary current affects the Hall element. A BiCMOS chopper stabilization circuit is utilized to reduce signal offset and to stabilize the output of the IC over its operating temperature range.[4] The on-chip electronics produce an analog voltage that is proportional to the input current.

    Figure 6. Block Diagram of the Circuit

    The output is ratiometric, which means that both the offset and sensitivity scale with VCC. Device accuracy is optimized through end-of-line trimming of the offset, sensitivity, and temperature response. The ICs are designed to measure both positive and negative currents, but the parameters can be trimmed for uni-directionality if required. The device is trimmed after packaging in order to reduce package stress effects on the Hall element. As shown in figure 6, an external bypass capacitor is recommended, to reduce noise. If the bandwidth of the application allows it, a simple rc filter can be used at the output to further improve signal-to-noise ratio.

    ±20 A Model Main Features Although the SOIC8 devices are designed for ±20 A, they can withstand large transient overcurrents of up to 100 A. The limiting factor determining the overcurrent capability of the devices is the junction temperature of the IC (TJ(max), which equals 165°C), and is therefore determined by the thermal design of the printed circuit board (PCB) in the application.

    The main features and benefits are summarized as follows:
    • AC and DC current measurement
    • 1.5 mΩ internal conductor resistance
    • 1600 VRMS (min) isolation voltage
    • 4.5 to 5.5 V supply operation
    • 50 kHz bandwidth
    • ±1.5% total output error at room temperature
    • operating temperature range of –40°C to 85°C
    • small footprint, low-profile SOIC8 package
    • near-zero magnetic hysteresis
    • ratiometric output from supply voltage
    • RoHS compliant (flip-chip high-temperature Pb-based solder balls are currently exempt from RoHS)

    ±200 A Model Main Features The thickness of the copper conductor allows survival of the device at up to 5× overcurrent conditions. The main features and benefits are summarized as follows:
    • AC and DC current measurement
    • 100 µΩ internal conductor resistance
    • 3000 VRMS (min) isolation voltage
    • 4.5 to 5.5 V supply operation
    • 35 to 50 kHz bandwidth
    • ±1.0% total output error at room temperature
    • operating temperature range –40°C to 150°C (a function of primary current)
    • small package size, easy mounting capability
    • ratiometric output from supply voltage
    • lead (Pb) free

    Recent Trends

    Current-sensing solutions for advanced industrial, automotive, commercial, and communications systems are facing new challenges. Although the solutions presented in the previous paragraphs are already covering a large variety of customer requirements, the general trend is clearly towards low cost, high accuracy, and small size systems, but with added functionality. This section describes two innovative devices developed at Allegro to address these needs.

    Improved IC Performance In an effort to further improve the characteristics of the ±20 A low-profile SOIC8, Allegro developed a third generation device with specific focus on noise and total output error reduction. The chip design was developed on the latest Allegro low-noise 0.65 µm BiCMOS process (DABIC6). A total of 23 programming bits can be used to optimize following IC parameters after packaging:
    • quiescent output voltage
    • sensitivity
    • sensitivity temperature coefficient

    The combination of improved process performance, new design concepts, and additional programming capability resulted in a 2× reduction in noise. The total output error at IP = ±20 A was improved from ±8.4% to ±1.5% in an industrial temperature range,  40°C to 85°C.

    This new device also has a filter pin that can be used to set the –3 dB point with a capacitor. This reduces the number of external components required to improve IC resolution (no sense resistor needed). The peak-to-peak current noise levels, for different filter capacitor values, at T = –40°C to 85°C, and IP = ±20 A

    Added Functionality

    For large volume applications, it may be worth integrating some additional functions on the Hall IC that would usually be realized with external components. In the implementation described below, this approach resulted in a new protection IC with integrated hot-swap gate driver and internal Hall-effect based element.
    The block diagram of this ACS760 device is shown in figure 7. The power supply load is measured without the use of an external sense resistor. The part uses an integrated 1.5 mΩ copper conductor and a Hall-effect element to accurately measure load currents up to 30 A. The device contains overcurrent protection circuitry that trips at a user-selectable level between 30 and 40 A. If an overcurrent condition is detected, the fault output of the part trips and the gate of the external mosfet is pulled to ground. The delay between the detection of an overcurrent condition and gate shutdown is set by an external capacitor.

    Figure 7. Block Diagram of the Protection IC,
    with Integrated Hot-Swap Gate Driver
    and Internal 1.5 Ω Hall-Effect Based Element

    Applications Examples

    This section gives two applications examples, in which the ACS devices support optimal current sensing solutions.

    Battery Monitoring Smart battery systems require circuitry to monitor cell voltages, temperatures, and currents. For capacity monitoring applications, all of these measurements are critical. The most difficult to design-in properly, however, is current measurement. The reasons for this are the requirements for accuracy, power dissipation, and solution size.

    Current measurement accuracy is essential to ensuring that the capacity monitoring algorithms are working well. The traditional method of measuring this current is with a shunt in the ground path or on the low side. The key problem with this method is that, to minimize I2R losses, the value of the shunt needs to remain very small. With this approach, low-current measurement accuracy becomes compromised. What it means for notebook computer applications is that during suspend, hibernate, or other low-power states, it is difficult for the battery to accurately monitor the current flowing into the system.

    If the battery is using a 10 mΩ sense resistor to minimize power dissipation at nominal loads, when in a low-power state with only 50 mA of power draw, the voltage across the shunt would be only 500 pV. This voltage is very difficult to resolve, and complicated algorithms for estimating the residual capacity must be developed for the battery in order to compensate for this effect. These routines are conservative in nature, meaning that they tend to assume that the battery is losing a little more capacity than is actually calculated. The result can be an appearance of excessive loss in battery capacity over time.

    Depending on the battery and the application, sense resistors in the range of 1 to 2 W would be required to monitor the currents. Typically in portable solutions, however, there is not enough space for 2 W resistors, so the solution is usually limited to 1 W resistors. For higher-current solutions, multiple resistors are used in parallel to keep the power ratings within the device limitations. Both solutions have a large impact on the board real estate required to fit these components.

    By using a Hall-effect device as a shunt solution in the battery pack, the power dissipation in the pack can be reduced. The advantage of using Hall-effect devices is readily apparent with the low insertion loss of the device. In an SOIC8 package, the ACS712 lead-frame insertion loss is only 1.5 mΩ. The difference in power consumption over a range of load currents is shown in figure 8.

    The use of a Hall-effect device as shown in figure 9 can increase the accuracy of current measurements. This block diagram shows a high current path and a low current path. The low-current path can be enabled for better accuracy at monitoring small currents. Not only does the solution shown in figure 9 provide higher accuracy for lower charge and discharge currents, but also it provides more signal than the shunt solution over the measurement range. Assuming that the Hall-effect device has a gain of 100 mV/A, this signal is much larger than the resulting signal across a shunt resistor, as shown below in figure 10.

    Figure 8. Power Loss in Shunt Versus Hall-Effect Current Sensing Solutions

    Figure 9. Improved Accuracy and Efficiency in Battery Monitoring with Hall-Effect Devices

    Figure 10. Output Voltage of a Hall-Effect Solution Compared to a 20 mΩ Shunt

    The step increase in gain with the Hall-effect solution assumes that the application enables the high current path shown in figure 9. The actual threshold for the transition and level of hysteresis desired will be a function of the application as well as the value of the shunt employed.

    The use of Hall-effect devices in battery systems will help to reduce the PCB area required for a shunt sensing solution and enable high-side sensing, which does not interrupt the ground path. The two major benefits in using a Hall-effect device are improving current measurement accuracy over a wider current range, and reducing power consumption by significantly reducing the 12R loss of the shunt.

    Hall Effect Devices in UPS and Inverter Applications The use of either Hall-effect devices or current transformers (CT) is common in UPS systems. While CTs are seen as low-cost solutions, they actually require more support components than a Hall-effect solution and are strictly limited to ac applications. Another secondary cost attributed to using CTs to monitor the AC line voltage is the additional circuitry to manage the effects of inrush and possible core saturation during an inrush event.

    UPS solutions require using the line voltage to charge a battery that is used to supply line voltage for a system in the event of a power failure. The goal of the UPS is to supply as much energy as possible with the maximum efficiency. For example, a 2200 VA UPS requires a typical 3-hour charge time. This same UPS can only supply approximately 24 minutes of power at half load (990 W) and 6.7 minutes at full load (1980 W). The input and output currents are monitored both for protection and to be able to show the battery state of charge with a level of confidence.

    The ACS712 Hall-effect device is ideal for monitoring the input power or battery charge current for several reasons. The obvious benefit for a small form-factor Hall-effect solution is that the volume required is a fraction of the equivalent CT solution, and in addition there is an elimination of gain and additional protection components. The reason for this is that the ACS712 cannot overshoot the voltage on the isolated side of the device.

    When powering the inverter stage at high loads, the optimal place to have the Hall-effect IC is at the line voltage itself to monitor the load currents directly. The reason is that the line voltage current may be as high as 15 to 20 ARMS, whereas the battery sourcing current may be in excess of 50 to 60 A, depending on the voltage of the battery stack and the efficiency of the converter. Below, figure 11 shows an example of using a Hall-effect device in a ups power train.

    Figure 11. UPS Power Train Architecture

    This next generation of Hall-effect devices is helping to resolve known issues with CTs and to improve the reliability of systems. By using Hall-effect devices in the battery charging system and inverter power train, the efficiency of the converters can be optimized. This can help to reduce the overall size of the system and save costs.


    Innovative current sensing solutions for industrial, automotive, commercial, and communications systems were presented. The packaged devices consist of a low-resistance primary current path and a monolithic linear Hall-effect IC that integrates the Hall element and state-of-the art BiCMOS interface circuitry.

    The devices cover a measurement range of up to ±200 A and can also be designed into higher current applications by using a current divider configuration. New approaches to address the trend towards low-cost, high accuracy, and small size current measurement systems with added functionality were detailed and two application examples presented.

    Nombre: Rodriguez B. Joiver I.
    Asignatura: CRF

    Managing External Magnetic Field Interference When Using ACS71x Current Sensor ICs


    The ACS71x families of Hall effect-based electrical current sensor ICs measure current by sensing the magnetic field it generates as it passes adjacent to the Hall element (see figure 1). They measure this field directly, without the use of a magnetic concentrator, which is a common feature in other magnetic devices (for example, in the Allegro® MicroSystems CA and CB packages, used for the ACS75x families of current sensor ICs).

    Figure 1. Current Path in an ACS71x Device

    Current passes in either direction through the U-loop and around the Hall element (X). The U-loop is mounted underneath the die in the SOIC8 package.

    The lack of a concentrator has the advantage of nearly eliminating magnetic hysteresis as a source of error in the IC. However, this also leaves the ACS71x devices less shielded from external magnetic fields that could distort the current measurement. In applications where large magnetic fields may be present, care must be taken in the alignment and spacing of the Hall element relative to those fields. Shielding the device may also be desirable in some circumstances.


    Flux lines form circles around a conductor in planes that are orthogonal to the direction of current flow through a conductor. The Hall element only responds to the flux component that is perpendicular to its surface, and is only susceptible to magnetic fields in this direction. As shown in figure 2, although the path of the primary current, IP, is in the same plane as the Hall element, the magnetic flux vectors generated by current passing through the U-loop are perpendicular to the Hall element plane. Those that intersect the Hall element induce a voltage across it, which is then amplified and used to generate the output voltage.

    Figure 2. U-Loop and Hall Element

    Current flowing through the U-loop generates flux lines in planes orthogonal to its path. Flux perpendicular to the plane of the Hall element can generate Hall voltage.

    High-current conductors in the vicinity of the device should be, if possible, oriented perpendicular to the plane on the board on which the device package is mounted. This is shown in figure 3. With this alignment, the magnetic flux would circulate in the plane of the Hall element rather than through it, and have little effect on the output of the Hall IC.
    Figure 3. Adjacent Conduction Perpendicular to Hall Element Plane

    Flux lines generated perpendicular to current flow are parallel to Hall plane and do not generate Hall voltage.

    Spacing and Layout Guidelines

    When laying out a PCB where the ACS71x device will be mounted, it is good practice to keep as much space as possible between the device and other traces carrying significant amounts of current. Figure 4 shows the measured effect of an adjacent current trace on the same side of the PCB as the device. Although this is a consideration for optimizing designs, the effect of the neighboring trace is small and much less than the signal generated by the current being measured within the device.

    Figure 4. Adjacent Conduction Traces Carrying 50 A, Effect on an ACS71x Device

    The minimal influence of magnetic effects from an adjacent trace diminish rapidly as the distance, D, is increased.


    Figure 4 shows the effect of the magnetic flux generated by an adjacent current-carrying trace on the Hall element when the current path is oriented in the same plane as the Hall element, and so its magnetic flux lines are perpendicular to the plane of the Hall element.

    If greater protection against external fields is needed, a surface mount magnetic alloy shield covering the device package is recommended. A shield such as the one depicted in figure 5 shunts external magnetic flux away from the SOIC8 package, and results in no significant effect on the magnetic field generated inside the package around the primary current path. Typical magnetic field results are depicted in figure 6.

    Figure 5. Simple Shield

    This design provides protection against perpendicular magnetic flux lines impinging from above an SOIC8-packaged Allegro current sensor IC. If necessary, a second shield can be placed on the opposite side of the PCB.

    Figure 6. Magnetic Field Map of Shield

    A simple ferrous alloy shield deflects virtually all perpendicular flux lines, effectively shielding the Hall element.

    The shield can be fastened to the PCB by epoxy, and is it not mandatory that it have a conductive path to ground. Because the Hall element is not susceptible to flux lines parallel to its plane, it is not necessary to enclose the sides of the shield. In fact, leaving the shield open in the vicinity of the IC leads is preferred for creepage and clearance considerations.

    In cases where a high level of shielding is required, a second shield of a similar type can be attached to the underside of the PCB, protecting the Hall element from the perpendicular flux passing through the PCB from below.

    Experimental Results

    An experiment was performed with ±240 G applied perpendicularly to the Hall element of an 8-pin device package, through the use of an air core field source. The attenuation levels achieved by shields constructed of various ferrous alloys and material thicknesses were recorded. The results are provided below. Two types of ferrous alloys were used, silicon steel (SiFe), and HyMu alloy, which is a generic class of alloys that have a high magnetic permeability level, µ. It should be noted that in most applications the Hall element will not be exposed to field levels as great as 60 G. For example, up to 60 G of field would pass through the Hall transducer only if the ACS71x were placed within 6 mm of an adjacent busbar carrying 500 A.


    The alignment, spacing, and shielding techniques described in this note may be used as increasingly aggressive steps to mitigate the effects of external magnetic fields when applying ACS71x current sensor ICs.

    If you need further assistance in dealing with the effects of external fields, please contact your local Allegro sales office to be put in touch with one of our applications engineers.

    Nombre: Rodriguez B. Joiver I.
    Asignatura: CRF

    Micro-Power Position Sensing in Cell Phone Applications

    Standard Slide or Flip Phone Configuration

    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.

    Using an omnipolar IC switch promotes ease of manufacturing, because the magnet can be inserted without concern about which pole is facing the Hall sensor IC—either the north or the south pole can be used to activate the IC switch. In the figure 2 example, the south pole is activating pole, as it is placed nearest the Hall sensor IC, but with an omnipolar sensor IC, placing the north pole on that side would work equally well.

    Figure 2. Hall-Effect Sensor IC and Magnet Positions on a Standard Slide Phone

    Figures 3 and 4 compare the transfer functions of an omnipolar switch (figure 3) to the well-known unipolar switch (figure 4). In both figures, the vertical axes are the output voltage response of the IC to an impinging magnetic field. Along the horizontal axes, increasing north polarity magnetic flux (increasing B–), increasing south polarity magnetic flux (increasing B+), and neutral polarity (B = 0) are shown.

    Figure 3. Transfer Functions

    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.

    Figure 4. Transfer Functions for Unipolar Hall-Effect IC Switches

    (A) magnetic flux effect on a north-polarity–activated switch, and (B) on a south-polarity–activated switch

    Dual-Mode IC Switches

    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

    The state of the SELECT pin determines the mode of operation for the A1171. When the pin is floated or tied to VCC, the part operates in omnipolar mode, as in figure 3. When the pin is grounded, the A1171 operates in a unipolar mode, as in figure 4. Notice that in omnipolar mode (figure 3) the separate outputs are complementary, while in unipolar mode (figure 4) the separate outputs are south- or north-pole activated switches.

    By using both outputs in unipolar mode, and orienting the sensed magnet, the A1171 can be used to sense three positions, supporting the broader range of articulating positions required in multipurpose phone applications. In unipolar mode, the VOUTPS pin is the output of a south-polarity–activated switch, and the VOUTPN pin is output of a north-polarity–activated switch.

    Multipurpose Multiposition Applications

    A multipurpose application is illustrated in figure 6. When the phone is fully closed (figure 6A), such as in MP3 applications, the south pole of the magnet is opposite the Hall sensor IC. The output of the A1171 is VOUTPS low and VOUTPN high, corresponding to the B+ side of figures 4A and 4B.

    In the slide-open position, used for the phone application (figure 6B), the Hall sensor IC is dominated by a north polarity field, and VOUTPN is low, while VOUTPS is high, corresponding to the B– side of figures 4A and 4B. Finally, in the rotate-open position, for texting or PDA use on a full keyboard (figure 6C), neither switch is subjected to a significant magnetic field, and both outputs are high (B = 0 in figures 4A and 4B).

    Figure 6. Multipurpose Application for Sliding and Rotating Phones

    The Output Truth Table summarizes all three phone positions and the resulting output states. This technique can be applied to rotating or sliding phones if mechanical placement and the sensing magnet are optimized.


    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.

    Nombre: Rodriguez B. Joiver I.
    Asignatura: CRF

    Integrating Hall-Effect Magnetic Sensing Technology into Modern Household Appliances


    As technology improves, Hall-effect sensor ICs are finding their way into many modern household appliances. The Hall effect refers to the measurable voltage that appears across a conductive material, for example silicon (Si), when an electric current flowing through the conductor is influenced by a magnetic field (see figure 1). Under these conditions a transverse voltage is generated perpendicular to the applied current due to the balancing of the Lorentz and Electromagnetic forces.

    Figure 1. The Hall Effect Refers to the Measurable Voltage Present,
    when an Applied Current is Influenced by a Perpendicular Magnetic Field

    Hall-effect sensor ICs have many advantages over traditional mechanical and reed devices. The contactless implementation of Hall sensor ICs improves reliability and durability by virtually eliminating mechanical wear and fatigue. These devices also have the ability to sense magnetic fields that are physically obstructed by nonferrous materials. The small, lightweight package sizes reduce implementation space and mechanical complexity. Many sensor ICs are user programmable to meet custom operational and accuracy requirements.


    There are several different types of Hall-effect devices suitable for various applications: Switches, Linears, Speed/Direction ICs, and Current Sensor ICs, to name a few.

    Switches and Linears

    Switches generate a digital output based on the magnetic operating (BOP) and release (BRP) points of the particular device. Linears generate an analog or pulse width modulated (PWM) output that is directly proportional to the applied magnetic field.

    In switch and linear applications, there are several possible magnet configurations for actuating the device. For example, the "head-on" mode of operation refers to moving the magnet perpendicular to the active face of the Hall device, as shown in figure 2.

    Figure 2. Head-on Hall Actuation

    TEAG is the total effective air gap.

    Alternatively, the "slide-by" mode of operation refers to moving the magnet parallel to the active face of the Hall device (see figure 3). The slide-by method typically results in better sensing precision than the head-on method due to its smaller magnet travel. The large magnetic slope between the poles makes it possible to obtain very precise switch point locations. However, the slide-by method also requires the use of strong magnets and a small total effective air gap (TEAG).

    Figure 3. Slide-By Actuation

    TEAG is the total effective air gap.

    Another method for actuating a Hall device is known as vane interrupter switching. A vane is a ferromagnetic material that has a unique configuration of notches cut into it. The vane can be custom shaped for linear or rotational motion. With vane interrupter switching, a magnet and Hall device are mounted in a stationary position such that the Hall device is forced into the "on" state by the activating magnet. When the ferrous material of the vane passes between the Hall device and activating magnet, the vane forms a magnetic shunt to divert the field away from the Hall device. The vane interrupter technique is frequently used where precision switching is required (see figure 4).

    Figure 4. Vane Interrupter Switching Hall Actuation

    Speed and Direction ICs

    A variation to vane interrupter switching is to use specialized back-biased Hall-effect devices (see figure 5). Back-biased devices can be used for proximity switching or gear tooth speed and angle sensing. With these devices, a rare-earth pellet and Hall sensor are integrated into a single package, reducing placement and alignment concerns. Back-biased sensor ICs are normally in the "off" state. When a ferrous material passes in front of the package the magnetic field is drawn through the active face of the Hall device, activating the IC.

    Figure 5. Gear Tooth Hall Actuation

    Current Sensor ICs

    Another use of the Hall effect is to sense current running through a wire or conductor. For small currents up to 20  A, the Hall die and the primary current path can be packaged together in a standard-footprint SOIC-8 surface mount package (see figure 6). The use of flip-chip technology leads to an optimized magnetic coupling between the active face of the Hall element and the field generated by the current to be sensed. This packaging technique eliminates the need for a flux concentrator.

    The internal resistance of the copper path used for current sensing is typically 1.5 mΩ for low power loss.

    Figure 6. Current Sensor Hall Device in SOIC-8 Package

    For larger currents up to 200  A, the dimensions of the copper conductor must be increased to account for the current density within the material. Because of the magnetic coupling between this thicker conductor and the linear Hall element, a flux concentrator must be used (see figure 7). A typical primary conductor resistance as low as 100 μΩ is achievable.

    Figure 7. Current Sensor IC Device for High Current (> 200 A) applications

    Hall-effect devices have the primary advantage over other current sensing technologies because the current sensing path is completely electrically isolated from the low voltage signal input/outputs.

    Application Examples

    Hall technology has been replacing conventional sensing techniques in many applications, including door switches, knob position, drum speed, water level measurement, and motor control. The selection of the appropriate Hall device depends on the level of accuracy and control required. This paper provides a sampling of how Hall technology can be utilized in modern household appliance applications.

    Knob Position

    Hall sensor ICs provide a contactless solution for determining an appliance's knob position. Several techniques are available for determining knob location. For example, if the application requires limited, discrete knob positions then simple switches such as the A1120 or A321x can be used. Each switch in the application represents a distinct position mark around the knob. When a magnet that is attached to the turning knob rests above one of the stationary switches, simple electronic logic can decipher which level has been selected.

    For higher accuracy applications, a linear device can be used in conjunction with a microprocessor. As the knob turns, the linear device provides the absolute analog position of the knob based on the decay of the magnetic field from the Hall element, while a lookup table in the microprocessor interprets the position of the magnet.

    The appropriate linear device depends on the desired accuracy in the application. Possibilities include the A132x or programmable A138x.

    The different output voltage responses from switch and linear implementations of knob position are shown in figure 8.

    Figure 8. Hall Switch Versus Linear Response to Knob Position

    Fluid Level Detection

    Switches and linears can also be used to monitor fluid levels, such as in washing machines or dishwashers. An easy technique for fluid level measurement is to use multiple Hall switches in conjunction with a magnet that is suspended in a float. As the float rises within a tube, it triggers discrete switches that are positioned outside of the tube housing, digitally indicating the water level (see figure 9). The A1120 would be an appropriate switch for this application.

    Figure 9. Fluid Level Sensing Technique Using Magnetic Float and Switch

    Hall technology can also be used to modify, rather than replace, traditional fluid level measurement techniques. For example, one approach currently used to determine when a drum is full is to expand a plastic diaphragm that pushes against a mechanical switch. An alternative to the mechanical switch assembly would be to implant a magnet into the diaphragm and suspend a Hall switch above it in a head-on configuration (see figure 10). Instead of a using switch, a higher resolution measurement can be achieved by using a linear. The linear solution will determine the absolute water level in the tank instead of merely indicating when the tank is full. Depending on the desired accuracy, a surface mount linear such as the A132x or programmable A138x would be suitable. In these applications, Hall has the advantage of reliability, durability, simplicity, size and weight when compared to mechanical cam based switches.

    Figure 10. Fluid Level Sensing Technique Using Inflatable Diaphragm Implementation

    Drum Rotation Detection

    Hall sensor ICs are useful for a variety of drum rotation sensing needs, such as speed, direction, and broken belt detection.

    A simple rotation indicator can be constructed by attaching a magnet to a spinning drum and using a stationary Hall switch. Each time the drum makes a full rotation the switch will send out a digital pulse. This signal can be used to simply indicate if the drum is spinning or can also be used by a microprocessor to calculate speed.

    If higher drum position accuracy is required, the angular position of the drum can be sensed using a differential Hall design, such as the A3425, in conjunction with a gear configuration as shown in figure 5. More sophisticated back-biased Hall configurations, such as the A3423, are capable of providing drum speed information and direction detection.

    In addition to sensing the position, speed and direction of a rotating drum, broken belt faults are also useful to detect. For example, if the heating element in a dryer fails to turn off when the dryer belt breaks, the lack of rotation can cause the clothing to catch on fire. Figure 11 shows a possible broken belt detection circuit that works using a magnet attached to a spinning drum and a stationary Hall switch. In this circuit, the central node charges at a rate determined by the R1C1 pair. When a magnet passes by the Hall switch, the IC VOUT signal undergoes a high-low-high transition. The rising edge of the VOUT signal temporarily turns on transistor Q1, discharging the central node. A broken belt will stop the drum from rotating, preventing the rising edge transition from occurring. This allows the central node to charge freely. When the central node reaches a voltage that turns on the Darlington pair, the circuit output switches to a digital low signal, indicating a broken belt fault.

    Figure 11. Broken Belt Detection Circuit Using Simple Hall Switch

    Motor Control

    Hall-effect current sensor ICs are a robust and simple means of monitoring motor currents for both control and protection. Motor current consumption is directly proportional to the torque the motor exerts. Therefore, a typical method of controlling the speed and applied force of a motor is to feed back its current consumption measurement into a microprocessor. The microprocessor can then calculate whether more or less current must be applied to the motor in order to achieve the desired speed. Hall-effect current sensor ICs can be placed directly in series with the motor (or any inductive load) because they have a very low resistance copper leadframe.

    Traditional techniques sense motor current using a shunt placed in the ground switch of a motor control assembly. With this approach, only half of the motor current can be monitored, which decreases accuracy and increases I2R losses. Hall-effect current sensor ICs have input supplies completely isolated from the current path, allowing for high accuracy and low power measurements. Allegro's ACS712 is available in an SOIC-8 package for use with small nominal currents, and the ACS75x is in a CB package for larger current sensing needs.

    Micro-Power Solutions

    As society continues to develop its understanding of environmental issues, the demand for low energy appliances grows stronger. The requirements of the US federal government's Energy Star program are becoming more and more stringent each year. Allegro MicroSystems is the first to offer micro-power Hall switches and linears to help manufacturers minimize their appliance energy consumption.

    The 321x family of switches uses a unique clocking scheme and 2.75 V nominal operating voltage to achieve a typical 15  μW of power consumption. The 139x family of linear Hall devices has a 3  V nominal operating voltage with 10 mW of power consumption in the active mode. The 139x devices also have a sleep pin that allows a microcontroller to disable the device, reducing power consumption to a nominal 75 μW (see figure 12). Additionally, when the 139X device is in sleep mode the output of the device transitions to a high impedance state. Therefore, multiple 139X linear Hall sensor ICs can be connected to a single analog-to-digital converter input as long as a polling scheme is used to monitor the output of a single A139X device at any point in time.

    Figure 12. Diagram of the 3 V, A139x Micro-Power Linear with Sleep Pin Input


    The applications described in this article are just a few examples of how Hall technology improves the performance and reliability of modern appliances over traditional implementation techniques.

    Nombre: Rodriguez B. Joiver I.
    Asignatura: CRF