Achieve greater precision,

reliability with integrated

magnetic sensing technology

Ricky Jackson,
Process Development Manager
Analog Technology Development
Texas Instruments

Keith R. Green, Ph.D.,

Distinguished Member of the Technical Staff
Analog Technology Development
Texas Instruments

Ross Eisenbeis,
Systems Engineer
Magnetic Sensing Products
Texas Instruments
Each time you climb into your car, you enter a world of
magnetic sensing, with tiny sensors reporting whether
the doors are closed and seat belts buckled properly.
Sensors also automatically guide seats into place, help
open windows, turn steering column switches on and
off, and track how you turn the steering wheel or press
the accelerator.
Several magnetic sensors are located, under the hood, detecting speed and position in
the cars engine, transmission and electric motors. Other sensors monitor fluid levels, track
body and wheel position, perform a number of safety checks, and sense currents for a
variety of electrical feedback and measurement functions.

A new automobile today may have as many as 70 bringing the advantages of miniaturization to what
magnetic sensors to enhance operation, safety and were once space-consuming devices. At the same
convenience. More are being added all the time due time, the cost of the permanent magnets integrated
to technology advancements that deliver greater within some magnetic sensors has dropped, helping
accuracy and reliability in smaller sizes with lower cost. push the trend toward affordability that comes with

The same trend can be observed in the electronic advanced manufacturing, as well as increasing

and electromechanical world in general. In addition functionality. The need for improved reliability,

to widespread use in vehicles, magnetic sensors safety and accuracy has motivated end product

find application in equipment including industrial developers to take advantage of the inexpensive

motors and robots, medical systems, office magnetic sensors that are now available on chips

machines, home appliances, and even handheld along with other circuitry. As a result, applications

tablets and cellphones. Like so many other are mushrooming, with a market estimated to pass

semiconductor devices that make the modern world $2 billion and 20 billion units in the next five years,

go round, magnetic sensors are invisible to end with the majority in the automotive segment.

users but indispensable for many of the functions Texas Instruments (TI) devotes significant
that we have come to take for granted. Figure 1 development effort to magnetic sensing. TIs portfolio
lists some of these uses. of magnetic sensors gives equipment manufacturers

What enables the ubiquity of magnetic sensors an array of options for their varied application

today is their small size and affordability. needs. The companys advanced analog process

Semiconductor manufacturers have applied technology makes possible the on-chip integration

advanced production techniques to enable analog of complete sensing solutions that include both

integrated circuit (IC) products that include sensors, the sensing element and other circuitry. TI process

Achieve greater precision, reliability with integrated magnetic sensing technology. I 2 June 2017
Automotive - Steering wheel angle, Non-automotive
electronically assisted
Powertrain Industrial Office machines
steering
- Crank and camshaft - DC motors - Fax machine door close
- Acceleration pedal
- Engine and transmission position - Heating, ventilation and air - Copier and printer paper
- Throttle position conditioning (HVAC) position level
- Passenger occupation
- Brushless DC motors - Elevator floor detection Medical
Body
- Hoist end position - Automated lab equipment
- Oil, brake, other fluid levels - Steering column control
- Deep bore liquid detection - Pacemaker
- Exhaust gas recirculation - Seatbelt presence
(EGR) position, current Digital still cameras - Hearing aid
- Seat position, electric
sensing and camcorders - Smart pills
windows and mirrors
Safety and vehicle control - Image stabilization
- Door latches, sunroof - Drug delivery fluid level
- Wheel speed - Motor commutation
Information Aerospace, marine
- Chassis height - Display open and close - Navigation compass
- Navigation compass
- Strut, suspension position Home appliances - Wind speed and direction
- Washing machine - Anchor, rudder, hatch
- Dishwasher position
- Instant water heater Mobile phones
- Coffee machine - Open and close
- Microwave oven - Electronic compass
- Cooker cover - Autofocus

Figure 1. The wide world of magnetic sensing.

innovation enabled the industrys first integrated required to replace them. Additionally, magnetic
fluxgate magnetic sensors for extremely high- sensors are largely unaffected by the presence of dirt,
precision measurement. For the growing world dust and even moisture when properly packaged.
of magnetic sensing, the companys technology This relative immunity to contamination provides a
continues to drive the development of solutions big advantage in the severe environment where most
for an ever-expanding range of end uses. factory equipment and car engines operate.

IC integration makes sensors small and cost-

Advantages of magnetic sensing
effective, and enables them to be combined
Because magnetic sensors do not require physical with circuitry for other operations. One important
contact, they help prevent wear on parts. For application use for integrated magnetic sensors is in
instance, magnetic sensors allow turn indicators and the control of motor drives, not only to replace DC
other switches on a steering column to switch on motor brushes but also to sense shunt currents for
and off without using mechanical contacts. Similarly, feedback on rotor position and speed in AC motors.
a brushless DC motor that uses magnetics to sense Position and speed encoder functions like these,
the electrical angle of the rotor avoids the eventual both rotational and linear, are also critical for motion
wearing away of brush contacts and the maintenance

Achieve greater precision, reliability with integrated magnetic sensing technology. I 3 June 2017
control, especially in robotics, where motion has to be field induces a voltage (VH), which can be amplified to
smooth and precise in three dimensions, often with provide a signal for readout or conversion and further
compensation for variable loads. processing. The simplicity of the Hall effect makes

Magnetic sensors can trigger various types of on-off for straightforward integration of the sensor element

latches for doors and covers, or for shutting down alongside analog and mixed-signal circuitry that may

equipment for safety, such as when a human being provide signal conversion, control functions and

comes dangerously near an industrial robot. The communications in the same device.

same principle can activate smoke alarms and other Fluxgate sensors perform more sensitive detection
devices to perform functions such as running self- of magnetic fields than Hall effect sensors and thus
test programs when a magnet is waved near them. tend to be used in applications where extremely high
Other designs provide a more linear signal output precision is required. Whereas the magnetic field
for monitoring currents. This feature is often used for detection range of Hall effect sensors is measured
circuit feedback and diagnostics in any number of throughout the millitesla (mT) range, fluxgate
electronic systems, for variable position and speed sensors can detect from very low milliteslas down
sensing, and for activating levels of response to into picoteslas (pT). Integrated fluxgate sensors
changing conditions in automobile engines, industrial are relatively immune to temperature changes and
processes, medical monitors and other areas.
B
Types of integrated magnetic
sensors +
-
There are a number of sensing methods based on I V_ -
- I
electromagnetic fields, each with its own operating
characteristics and level of affordability. Two
significant types of sensors that lend themselves to Figure 2. The Hall effect produces a measurable voltage proportional to
integration in silicon processes are Hall effect and the interacting electric current and magnetic field.
fluxgate magnetic sensors.

Hall effect sensors are the most popular magnetic introduces very little noise and baseline offset in the

sensors. They are robust, with high voltage ratings, output. They offer fast, high-resolution response with

a wide operating range without saturation in intense low parasitics to a magnetic field in a single axis.

magnetic fields, and utility in multi-axis (multi- Because of their high level of sensitivity, these types of

directional) magnetic fields. In chip integration, sensors must be carefully shielded in the application

these sensors require no additional steps or unusual to avoid field saturation and interference from stray

materials. This makes the manufacturing process magnetic fields.

economical and enables the creation of cost- Fluxgate magnetic sensor operation is based on two
effective IC solutions for many applications. solenoid coilsan excitation or drive coil and a pick-

Figure 2 shows the principle of Hall effect operation. up coil. An alternating current through the excitation

When a magnetic field is present at a right angle to coil creates a magnetic field that induces a current

the current flowing through a conductor, a voltage in the pick-up coil. In a magnetically neutral field, the

potential, called Hall voltage, is developed. This input current to the excitation coil and output current

Achieve greater precision, reliability with integrated magnetic sensing technology. I 4 June 2017
 from the pick-up coil are identical and cancel each and in-depth development support for the devices
other. If there is a difference between them that helps simplify the design process.
creates a detectable output current, it results from Equipment manufacturers use TIs digital and
the presence of an ambient magnetic field. The analog Hall effect sensors for position, speed and
design of the device provides for reading the level acceleration detection, object recognition, index
of this difference as a measurement of the ambient counting and other applications. Selections offer
magnetic field. robust protection, with best-in-class operating
Figure 3 illustrates the architecture of fluxgate sensors voltages up to 38 volts (V) and temperature up to
as implemented with TIs manufacturing process. 175C. The recently released DRV5032 ultra-low-
Notable architectural enhancements include the power sensor draws less than 1 microamp (A),
use of two cores and a third coil for compensation. helping prolong charge life in battery-powered
Known as a Frster-type fluxgate, this differential applications. Extremely small package options help
architecture cancels offset, improves output linearity, reduce the bill of materials and board space for
and extends the sensing range up to 2 mT. cost-optimized designs. Digital sensors offer latch,
unipolar and omnipolar switch sensor functions,
TI innovation in magnetic sensing while analog sensors provide a linear output for
solutions bipolar sensing that is fully protected with reverse
TI offers solutions that integrate either Hall effect battery and load dump protection of up to 40 V.
or fluxgate magnetic sensors. The operating Reference design and evaluation modules (EVMs)
characteristics of these two sensor types that speed development time with TIs Hall effect
complement each other, allowing application sensors include an incremental rotary encoder
developers to select the most optimum sensor using contactless magnetic sensing in vehicles, a
for a wide range of requirements. TIs integration 24-V brushless DC outrunner motor with closed-
capabilities provide a variety of on-chip functions, loop speed control, and low-power magnetic
tamper detection.
Excitation
Flux
Compensation
Direction
To achieve the industrys highest resolution in on-
Sense
chip magnetic sensing, TI has developed fluxgate
sensor products based on a unique manufacturing
process. These fluxgate sensors lend themselves
to high-voltage uses and are well suited for precise
Sense
Volt (+) applications such as motor control and battery
monitoring. TI selections provide open- and closed-
Sense
Volt (-) loop options with integrated signal conditioning,
degauss and diagnostic features. Time-saving

Sense
reference designs and EVMs provide accurate
Mid measurement for three-phase inverter currents up to
Excitation Flux
Compensation 150 A (maximum), a 100-A bus bar current sensor
Direction
Sense for single-supply open-loop current sensing, and
a displacement sensor with non-isolated high-side
Figure 3. The Frster-type fluxgate includes two parallel magnetic cores
and three sets of interwound solenoid coils. current and voltage sensing.

Achieve greater precision, reliability with integrated magnetic sensing technology. I 5 June 2017
 Typical Application
3.3 V or 5 V optional

magnetic
core
RSHUNT

DRV421
Fluxgate Sensor Front-End Shunt
Sense
H-Bridge Amplifier
Driver
DRV421

Integrator
Fluxgate
and
Sensor
Filter

compensation ADC
coil

Device Control and Degaussing Reference

return current primary
conductor current
(optional) conductor

RSHUNT
Figure 4. High-resolution DRV421 and DRV425
integrated fluxgate magnetic sensors simplify COMP1 COMP2 DRV2 DRV1 AINP AINN
closed- and open-loop current-sensing designs. DRV425
Shunt
Differential
Figure 4 illustrates the extent of Fluxgate
Driver
Sense
Amplifier
Sensor
internal integration in two of TIs and Integrator
Compensation
fluxgate sensors, the DRV421 and Coil
VOUT
ADC
DRV425, plus how these devices are Fluxgate Sensor Front-End REFIN

tailored for use in closed- and open- Device Control and Diagnostic Reference
REFOUT
loop designs.

The technology at the heart of these

products was developed by TI to A future of magnetic sensing
enable the production of the industrys first current- Magnetic sensing is increasingly important in almost
sensing IC with a fully integrated fluxgate device all fields of electrically operated systems. Vehicles,
and compensation coil driver. Complementing industrial equipment, medical diagnostics, home
the sensing element itself are novel excitation and office appliances, personal electronics
and readout circuits created for high-precision these and other applications are rapidly adopting
measurements. An innovative technology requires magnetic sensors for sensing position, speed,
advanced characterization methodologies, which current, and measurement of a variety of other
were specifically developed for the stand-alone conditions. Magnetic sensors provide precise,
fluxgate device using a conventional method of reliable output that is extending the reach of
extracting the second-order harmonic at the developers in many directions.
sensor output.

Achieve greater precision, reliability with integrated magnetic sensing technology. I 6 June 2017
TIs innovative analog technology differentiates the References:
companys Hall effect sensor products by providing
D. Lee, M. Eissa, A. Gabreys, B.Shulver, E. Mazzotti,
exceptionally high-voltage and low-current operation.
S. Lavangkul, S. Chavacharoenkul, N. Murphy,
The companys analog technology also enabled
F. Want, Y. Zhang, W. French, M. Jenson and R.
the industrys first integrated fluxgate sensors for
Jackson (2017). Fabrication and Performance of
outstandingly high-resolution output. TIs wide range
Integrated Fluxgate for Current Sensing Applications.
of other products makes possible a great variety of
Intermag 2017. April 24 28, 2017. Dublin, Ireland.
multi-functional integrated sensing solutions in the
Martin F. Snoeiji, Viola Schaffer, Sudarshan
future to meet our customers requirements. With
Udayashankar, Mikhail V. Ivanov, Texas Instruments
the breadth and depth of TIs process technology,
(2017). An integrated fluxgate magnometer for
manufacturing and design expertise at work to
use in closed-loop/open-loop isolated current
develop new sensing solutions, the future of sensing
sensing. European Solid-State Circuits Conference
promises to be magnetic.
(ESSCIRC). September 14-18, 2015. Graz, Austria.
For more information, check out:
TIs DRV5032 ultra low power sensor

TIs DRV421 and DRV425 fluxgate sensors

TIs complete sensing product portfolio

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