DIODES AN1187 Hall Effect IC Applications User Guide

DIODES AN1187 Hall Effect IC Applications

Specifications

• Product Name: AN1187 Hall-Effect IC Applications Guide
• Author: Alex Jih
• Application Manager: Hall Sensor Design and Application Manager, Standard Analog Business Unit
• Website: www.diodes.com

Product Information

Introduction
The Hall effect was discovered by Dr. Edwin Hall in 1879. When a current- carrying conductor is placed in a magnetic field, a voltage is generated perpendicular to both the current and the field, known as the Hall effect.

Hall Element Architecture
The Hall element architecture consists of a thin sheet of semiconducting material through which current is passed. Output connections are perpendicular to the current direction. A magnetic field causes a potential difference (Hall voltage) across the output.

Electrical Considerations

• Output transfer function
• Output functionality

Magnetic Fields
Magnetic fields are described by lines of flux originating from the north pole of a magnet and terminating at its south pole. Flux density is used to measure the intensity of the magnetic field at a point in space.

Product Usage Instructions

How Does the Hall Effect Work?

1. Place the current-carrying conductor into a magnetic field.
2. A voltage will be generated perpendicular to both the current and the field.

Using Hall Element Architecture

1. Connect the Hall element to the circuit with proper orientation.
2. Apply current to the Hall element.
3. Introduce a magnetic field perpendicular to the Hall element to observe the Hall voltage output.

Magnetic Flux Density Calculation

1. Calculate the flux density using the provided tool in the Appendix section of the manual.
2. Ensure that the distance between magnets and the Hall element is within effective sensing range.

FAQ

• What is the unit of measurement for magnetic field in Diodes Incorporated’s Hall sensor products?
  In Diodes Incorporated’s products, the unit of magnetic field measurement is Gauss (Gs).

• How can I ensure effective magnetic sensing with the Hall element?
  To ensure effective sensing, maintain a short distance between magnets and the Hall element as magnetic sensing is only effective at short distances.

AN1187
Hall-Effect IC Applications Guide
Alex Jih, Hall Sensor Design and Application Manager, Standard Analog Business Unit

AN1187 – Rev 1 Application Note
March 2024
© 2024 Copyright Diodes Incorporated. All Rights Reserved.
www.diodes.com

Introduction

• The Hall effect was discovered by Dr. Edwin Hall in 1879 while he was a doctoral candidate at Johns Hopkins University in Baltimore.
• Dr. Hall found when a magnet was placed so that its field was perpendicular to one face of a thin rectangle of gold through which current was flowing, a difference in potential appeared at the opposite edges. He found that this voltage was proportional to the current flowing through the conductor, and the flux density or magnetic induction perpendicular to the conductor.
• How does the Hall Effect work?
  • When a current-carrying conductor is placed into a magnetic field, a voltage will be generated perpendicular to both the current and the field. This principle is known as the Hall effect.
  • The fundamental physical principle behind the Hall effect is the Lorentz force, when an electron moves along a direction, v, perpendicular to the applied magnetic field, B, it experiences a force, F, the Lorentz force as Figure 1.
• Figure 2 illustrates the basic principle of the Hall effect. It shows a thin sheet of semiconducting material (Hall element) through which a current is passed. The output connections are perpendicular to the direction of current. When no magnetic field is present, current distribution is uniform and no potential difference is seen across the output shown in Figure 2.
• When a perpendicular magnetic field is present, as shown in Figure 3, a Lorentz force is exerted on the current. This force disturbs the current distribution, resulting in a potential difference (voltage) across the output. This voltage is the Hall voltage (VH).
• The interaction of the magnetic field and the current as VH ∝ I × B.

Magnetic fields

• The physical force exerted by a magnet can be described as lines of flux originating at the north pole of a magnet and terminating at its south pole shown in Figure 4.
• In general hall sensor applications, the concept of flux density is used to describe the intensity of the magnetic field at a particular point in space. Flux density is used as the measure of magnetic field. Units of flux density include teslas(T) and webers/meter2, The cgs unit of magnetic field, Gauss(Gs) is unit used in Diodes Incorporated’s (Diodes) Hall sensor products.
• Besides, 1T=104 Gs.
• Additionally, the magnetic flux density is proportional to the inverse square of the distance. B ∝ 1/d2, d is distance between magnets to hall element. This means that magnetic sensing is only effective at short distances.

Hall Element Architecture

Orientation of Magnet field

For Hall devices, orientation of the field relative to the device active area is important. The active area (Hall element) of Hall devices is embedded on a silicon chip located parallel to, and slightly inside of, one particular face of the package. That face is referred to as the branded face because it is normally the face that is marked with the part number (detail information please refer to the datasheet). To optimally operate the switch, the magnetic flux lines must be oriented to cross perpendicularly through the active area (the branded face of planar Hall devices, or the sensitive edge of vertical Hall devices) and must have the correct polarity as it crosses through.

Planar Hall Device

Electrical Considerations

Output transfer function

• Hall sensor functionality is fundamentally linear however most devices available fit into the “digital switch” whose output is On or Off depending on the applied magnetic field.
• These digital switches can have Unipolar transfer function (responds to only one type of pole), Omnipolar (responds to either pole) and Latch (turns on with one pole and only turns off with the opposite pole).
• In addition to these switches, ratiometric linear hall sensors are available (output is proportional to magnetic flux density detected).
• Their characteristics are shown below:

Specification definitions

• B(Gs): Magnetic flux density of South pole including X, Y, and Z axis.
• -B(Gs): Magnetic flux density of North pole including X, Y, and Z axis.
• BOP: Magnetic operating point, defines when the output driver will be active (On)
• BRP: Magnetic Release point, defines when the output driver will be inactive (Off)
• BHYS: Difference between Bop and Brp, BHYS = Bop-Brp
• d: distance between Magnet to Hall device branded side
• On: Output at low state
• Off: Output at high state

Unipolar

Omnipolar

Latch

Ratiometric Linear

Output Functionality
Digital output switches have a variety of output formats including push-pull, built-in pull-up resistor, open-drain/-collector, and current-output.
Diodes’ linear/analog output devices have their output voltage ratio metric to the supply voltage.

Specification definitions

• VOH: Output high voltage depends on output current at datasheet
• VOL: Output low voltage depends on output current at datasheet
• RUP: pull-up resistor
• CL: Output capacitor(optional)
• ION: Supply current on state
• IOFF: Supply current off state
• VSEN: Output Voltage Sensitivity
• VNULL: Quiescent Output Voltage with Zero Gauss

Digital Output

1. Push-pull and built-in Pull-up resistor
2. Built-in Pull-up resistor (RUP) versions have their resistance in the 10k to 100kΩ range, which is usually larger than Push-pull version (PMOS RON lower than 1kΩ). This makes their output source current poor, especially with the 100kΩ pull-up resistor devices and so these quite often have to add a buffer to drive next stage.
3. The optimum CL design value depends on system requirements. However, please note that a larger capacitance value will increase the output rise/fall time which slows down the response time/frequency.
4. Open drain/collector
5. Devices with an open drain output with external pull-up resistor (RUP) allows the output to be referred to supply rails. One option is to refer the Pull-up resistor (RUP) to the same power rail as the hall sensor and ECU resulting them all employing the same power as like VddA. Another where the hall sensor and the ECU are powered from separate rails, VddA and VddB. Here the Hall device uses VddA while the pull-up resistor is referred to the same power rail as the ECU (VddB).
6. VddB voltage can be either lower or higher than VddA and is based on the application. Please note – the VddB voltage can’t operate higher than the open drain absolute maximum ratings shown in datasheet.
7. The optimum CL (filtering capacitor) design depends on system requirements. However, please note that the bigger capacitance value will increase the output rising/falling time and slow down the switching frequency. The switching frequency can be calculated by below equation:
8. Current output
9. In general, the current output is suitable for us e in long cable wires for cost reduction and for enhanced noise immunity. In applications, it is necessary to add resistor (RSES) in series to Hall device GND pin and close to ECU, then the output current (ISES) will be converted to voltage (VSES). The RSES value is dependent on the application, but please note that the current output type minimum operating voltage will be limited by VSES.
10. For example:
    Assume the Hall device min operating voltage (VDDmin) is 2.7V, ION=14mA, IOFF=6mA, RSES =100Ω
    VSES_ON = ION RSES=14mA100Ω=1.4V, critical parameter
    VSES_OFF = IOFF RSES=6mA100Ω=0.6V
    Thus, the system power applied to hall device have  to higher than 4.1V (VSES_ON+VDDmin=1.4v+2.7V) to ensure function working normal.

Analog Output

• The output voltage is proportional to magnetic flux density and is calculated by the formula:
  Vout = VNULL+Gs*VSES

• Where:

  • VSEN is Output Voltage Sensitivity in mV/Gauss – and depends on product specification.
  • VNULL is nominal Output Voltage with zero gauss applied; Vdd/2 is general case

• For example:

  • Assume operating Vdd is 5V, VNULL is 2.5V(= Vdd/2), VSEN is 2.5mV/Gauss
  • The linear output voltage range is specified as VOH maximum 4.8V to VOL minimum 0.2V individually. From these the maximum and minimum operating gauss range and Vout at specific gauss can be calculated based on the information above.

• S_Gmax

  • (VOH-VNULL)/VSEN =(4.8V-2.5V)/(2.5mv/G) = 920G N_Gmin
  • (VOL-VNULL)/VSEN =(0.2V-2.5V)/(2.5mV/G) = -920G Vout @ 100G
  • Vout = VNULL+GsVSES =2.5V+100G(2.5mV/G)=2.7V Vout @ -100G
  • Vout = VNULL+GsVSES =2.5V+(-100G)(2.5mV/G)=2.3V

Design Example: 2-in-1/360° laptop mode detection
A 2-in-1 Laptop employing AH1389 dual unipolar output product is used to detect the swap to Laptop mode or Tablet mode using the AH1389’s two output signal combination.

• Closed mode: Display panel rotated angle close to 0° from hinge
• Laptop mode: Display panel rotated angle > 0° and < 180° from hinge.
• Tablet mode: Display panel rotated approach to 360° from hinge

Hall Product: AH1389 Dual Unipolar characteristics

Output State

Magnet material example

• ✓ Magnet grade: NdFeB, N52, L 9.0mm,W:5.0mm, H:2.3mm
• ✓ Rmanence: 1.43kGauss(min) ~1.49kGauss(max)
• ✓ Coercive Force bHc: 860KA/m
• ✓ Direction of magnetization (Oriented through length)

Magnet and Hall sensor position in laptop design (dimensions not to scale)

Note: 1. -2mm ~ +2mm is fine to symbol C and C1

Example: Magnetic flux density vs. Panel rotating angle (Ө)/Output state

• Open condition: with the hinge rotated angle larger than 12°, the laptop will enter Laptop mode from closed mode. Closed condition is when the hinge angle is less than 8°.
• Tablet mode:
  • With the hinge rotated angle is larger than 352°, if the angle is less than 348° then the laptop will go back to laptop mode.
  • The example above shows the ideal case; for more information about the magnet material/shape and position, and how these correspond to Diodes’ Dual unipolar design please contact Diodes.

Appendix

Magnetic flux density calculation tool:
https://www.diodes.com/products/analog/sensors/hall-effect-latches-and- switches/hall-effect-sensors-part-selector/

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