US5781LSE Melexis Inc, US5781LSE Datasheet - Page 29

• Manufacturer Part Number: US5781LSE
• Description: IC HALL EFFECT SWITCH TSOT-23
• Manufacturer: Melexis Inc
• Type: Unipolar Switchr

Specifications of US5781LSE

• Sensing Range: 15mT Trip, 3.5mT Release
• Voltage - Supply: 3.5 V ~ 24 V
• Current - Supply: 5mA
• Current - Output (max): 50mA
• Output Type: Digital, Open Drain
• Operating Temperature: -40°C ~ 150°C
• Package / Case: SOT-23
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Features: -
• Other names: US5781LSETR

Electromagnets
Another method of actuating Hall Effect Sensors is through the use of electromagnets. They are especial-
ly useful in circuit-breaking or current-sensing applications because their magnetism can be “turned on”
or “turned off” at will. An electromagnet consists of a coil of wire which may be wrapped around ferrous
material or core. The strength of this magnetic field is dependent on many variables, such as the perme-
ability of the ferrous material, the number of times the coil is wrapped around the material, the amount of
current flowing through the coil and the length of the core. These variables are related to each other in the
same way for all types of electromagnets, but the formulas differ slightly due to the variance of shape in
core material.
Figure 14, Common Electromagnet Shapes
Where:B = magnetic flux density
u0 = permeability of core material
N = number of turns made by coil
i = amount of current in coil
R = mean radius of toroid
Where:
B = magnetic flux density
u0 = permeability of core material
N = number of turns made by coil
i = amount of current in coil
l = length of cylindrical core
After choosing a core that will physically fit into the proposed current-sensing system, the values of length
of radius, permeability and at what value the current limiter is to operate will be known. The operate point
and release point for each Melexis Hall IC can be located in the datasheet section of this manual. By
knowing this information, it is now possible to calculate how many turns of wire will be required to pro-
duce enough flux density to actuate the Hall Effect Sensor. When designing an electromagnet use mate-
rials with the following properties: High saturation induction and high permeability will produce strong
magnetic fields resulting in a smaller device that will operate with little energy. When an electromagnet
is being switched on and off, use a material with a low coercive force for faster magnetization and demag-
netization. Also pay attention to magnetic aging and mechanical characteristics such as corrosion. This is
Section 3 - Applications
3-13