US5781LSE Melexis Inc, US5781LSE Datasheet - Page 38

• 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

Gear Tooth Sensor Magnetics
In order to detect the passing gear teeth with a Hall effect sensor it is necessary to provide a source of
magnetic energy. The simple way to do this is to arrange a permanent magnet such that the axis of mag-
netization is pointing toward to surface of the gear teeth. As a tooth moves across the surface of the
magnet the flux will become attracted to the lower reluctance path provided by the ferrous steel struc-
ture. When this occurs the flux density measured by the Hall element between the face of the sensor and
the gear tooth increases. Many schemes have been developed and some patented that use the various
attributes of the vector flux field and its changing nature to create zero speed Hall effect gear tooth sen-
sors. Melexis has chosen to work with digital signal processing schemes and in this way minimize the
magnetic circuit manipulation required of the end user. Put simply, by applying silicon "smarts" the
magnetic subtlety and slight of hand is nearly eliminated.
Figure 25, Geartooth Flux Transitions
Magnetic modeling courtesy of AnSoft TM magnetic modeling software.