US5781LSE Melexis Inc, US5781LSE Datasheet - Page 37

• 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

Geartooth Sensor
Magnetic Geartooth Sensing
The need to sense speed and position of ferrous gears occurs in numerous industries. The ability to con-
vert the repetitive passing teeth to an electrical impulse has been sought for many decades. purely
mechanical systems have been used with the attendant issue of wear and failure limiting its use to low
speed and low duty cycle applications.
Hall-Effect geartooth sensing makes use of the Hall element to sense the variation in flux found in the air-
gap between a magnet and passing ferrous gearteeth. A modern approach is to convert the signal from the
Hall element to a digital value and then perform signal processing to create a digital output from that
effort. In the case of the Melexis geartooth sensing scheme each time the signal changes direction a
counter is reset. If the signal level changes beyond the preset magnitude from the positive or negative peak
the output level is changed. This creates a digital zero speed peak detection speed sensor. It is immune to
orientation requirements and cab follow the gear speed down to the cessation of motion. It will detect the
first edge of the next tooth after immediately after power on. The digital signal processing does introduce
an uncertainty from quantization that is greater at larger speeds. Extremely demanding timing require-
ments like those found in crank position sensors may suffer from the loss of accuracy at high speeds.
Figure 24 shows the Melexis MLX90217 geartooth sensor operation.
Figure 24, Geartooth Sensor
Section 3 - Applications
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