US3881LSE Melexis Inc, US3881LSE Datasheet - Page 38

• Manufacturer Part Number: US3881LSE
• Description: IC HALL LATCH NORTH POLE TSOT-3L
• Manufacturer: Melexis Inc
• Type: Digital Latchr

Specifications of US3881LSE

• Sensing Range: 9mT Trip, -9mT Release
• Voltage - Supply: 2.2 V ~ 18 V
• Current - Supply: 5mA
• Current - Output (max): 50mA
• Output Type: Digital, Open Drain
• Operating Temperature: -40°C ~ 150°C
• Package / Case: TSOT-23-3, TSOT-3
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Features: -
• Other names: US3881LSETR

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.