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Chopper stabilized amplifier stage2£®Description
The S648 Omnipolar Hall effect  sensor IC is fabricated from
mixed signal CMOS technology .It incorporates advanced
chopper-stabilization techniques to provide accurate and stable
magnetic switch points.
The circuit design provides an internally controlled clocking
mechanism to cycle power to the Hall element and analog
signal processing circuits. This serves to place the high
current-consuming portions of the circuit into a ¡°Sleep¡± mode.
Periodically the device is ¡°Awakened¡± by this internal logic
and the magnetic flux from the Hall element is evaluated
against the predefined thresholds. If the flux density is above
or below the Bop/Brp thresholds then the output transistor is
driven to change states accordingly. While in the ¡°Sleep¡± cycle
the output transistor is latched in its previous state. The design
has been optimized for service in applications requiring
extended operating lifetime in battery powered systems.
The output transistor of the S648 will be latched on (Bop) in
the presence of a sufficiently strong South or North magnetic
field facing the marked side of the package. The output will be
latched off (Brp) in the absence of a magnetic field. 

Features
  Micropower consumption for battery powered applications
  Omnipolar, output switches with absolute value of North or South pole from magnet
  Operation down to 2.5V
  High sensitivity for direct reed switch replacement applications