PRELIMINARY TECHNICAL DATA
Wheel Speed Sensor For
Preliminary Technical Data
Speed and direction from 0Hz to 2500Hz
Air gap diagnostics
2-wire current-loop operation
Wide Operating Temperature Range
Functional during temperature excursions to 190C
Reverse Supply Protected (-30V)
Wheel speed and direction sensing
Transmission speed sensing
Incremental position sensing
Functional Block Diagram
The AD22157 is a mixed signal magnetic field transducer
designed for applications where both speed sensing and direc-
tion sensing of a ferrous target wheel are required over a wide
The device operates from a 2 wire high compliance current loop
and is suitable for continuous operation from -40C to 150C with
supplies up to +20 Vdc. The sensor is designed to remain func-
tional during voltage transients up to +27V.
The sensor output format is a current pulse from 7mA to 14mA
(the quiescent bias is 7mA) whose rising edge is accurately
placed relative to the edges of the target wheel. The pulse width
is determined by both target wheel direction and field strength.
The output pulse is coded in multiples of a well defined time
interval depending on direction and field strength in conform-
ance with industry standards currently being promoted by lead-
ing systems manufacturers.
Pulse widths corresponding to differential magnetic fields mea-
sured at the sensor of ∆B >4mT (normal operation),
2mT<∆B<4mT (low field range), and ∆B<2mT (very low field
range) are provided. Direction is indicated in the normal and
A fail safe stop signal repeating at approximately 1.5Hz is pro-
vided initially at power on, if the target wheel is stopped, or if
no dynamic signal is detected for some other reason.
The sensor combines integrated bulk Hall cell technology and
instrumentation circuitry to minimize temperature related drifts
Information furnished by Analog Devices is believed to be accurate and reliable.
However, no responsibility is assumed by Analog Devices for its use, nor for any
infringements of patents or other rights of third parties which may result from its use.
No license is granted by implication or otherwise under any patent or patent rights of
associated with Hall cell characteristics. The sensor is compen-
sated to work optimally with SmCo magnets. The architecture
maximizes the advantages of fine line CMOS and high voltage
DMOS allowing the device to operate accurately in demanding
Principle features of the AD22157 include an adaptive differen-
tial zero crossing detector which accurately determines the posi-
tion of target wheel edges. This architecture eliminates the
effects of package and thermal stress on the Hall sensor array
resulting in 2% repeatability of the time interval from rising
edge to rising edge of the sensor output.
The sensor takes 4 edges from either power on or a stopped con-
dition to achieve full accuracy. The architecture employs digital
signal processing to provide robust functionality and eliminate
spurious or missing pulses under extreme conditions of EMC.
The AD22157 is housed in a 5 lead single-in-line (SIP) package
suitable for mounting with a back biasing magnet in a typical
wheel speed sensor assembly.
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Analog Devices, Inc.,2001