Compact and easy to design in, our KMI magnetoresistive sensors provide simple and
cost-effective solutions for all your rotational speed measurement needs. They meet the high
EMC, reliability and temperature range requirements of the automotive sector, and are available
in a range of options to maximize design freedom.
Key benefits
Ñ
Wide air gap between sensor and target
Ñ
Speed detection down to 0 Hz
Ñ
Very low jitter
Ñ
Wide frequency range
Ñ
Insensitive to vibrations
Ñ
Temperature range: -40 to +150 ºC
Ñ
Prepared for injection moulding
Key applications
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ABS
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Engine management
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Gearbox
Ñ
Transmission systems
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Vehicle speed
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DC motor commutation
Accurate rotational speed measurement is a vital component
in maintaining performance, safety and reliability in modern
vehicles. It forms the basis of numerous applications from anti-lock
braking to engine management systems, and opens the way for
embedding intelligence throughout the car with the introduction
of advanced X-by-wire networks and control systems.
Component detail of the KMI20
NXP’s KMI family of magnetoresistive (MR) rotational speed
sensors provides a solution for all applications. Designed
specifically to meet the needs of automotive systems,
they are complete, ready-to-use modules comprising sensor,
back-biasing magnet and advanced signal conditioning IC.
Enabling maximum design flexibility, the devices are available
with a choice of output signals and individually magnetized
back-biasing magnets.
“ Ears “ to fix the position
of the sensor chip during
moulding process
Extra thick leadframe material
for robustness, bendable
Conditioning IC
MR-sensor
Conditioning IC
How to measure rotation with MR sensors
The KMI sensors are designed to sense the motion of ferrous gear wheels or of magnetized targets. A periodic magnetic field
stemming from the effect of flux bending by ferrous gear wheels or directly from magnetized targets will be transformed by
a MR sensor into an analog electrical signal. The frequency of this signal is proportional to the rotational speed of the target.
gear wheel or rack
magnet
magnetic field lines
direction of motion
S
magnetic field lines
magnetized target
N
sensor
(a)
V
t
N
MBE073
(b)
(c)
(d)
S
sensor
amplifier,
comparator
current
14 mA
7 mA
position
msc655
A subsequent integrated circuit transforms the analogue into a digital output signal. The output level is independent of the sensing distance within the
measurement range.
Back-biasing magnets, individually magnetized
for each sensor
Ñ
Large (8.0 x 8.0 x 4.5 mm) – for maximum air gap
between sensor and ferrous targets
Ñ
Medium (5.5 x 5.5 x 3.0 mm) – for use with ferrous
targets where space is limited
Ñ
Small (3.8 x 2.0 x 0.8 mm) – for magnetized targets,
stabilizing the inherently bi-stable MR sensor
Output signals
For high flexibility in the design of the subsequent signal
conditioning electronics, the KMI sensors are available
with:
Ñ
a digital current output signal (2-wire)
Ñ
an open collector output signal (3-wire)
KMIXY/1
mbh778
KMIXY/4
mbh779
KMIXY/2
mbh777
KMI15 – 7/14 mA current output (2-wire)
KMI18 – open collector output (3-wire)
CONSTANT
CURRENT
SOURCE
VOLTAGE CONTROL
V
CC
VOLTAGE CONTROL
V
CC
SENSOR
AMPLIFIER
SCHMITT
TRIGGER
SENSOR
AMPLIFIER
SCHMITT
TRIGGER
SWITCHABLE
CURRENT
SOURCE
V
out
open collector
output
V-
GND
mra958
mgl348
The MR sensor signal is amplified, temperature compensated and passed to a Schmitt trigger.
KMI20 – 7/14 mA current output (2-wire), extended air gap
VOLTAGE CONTROL
CONSTANT
CURRENT
SOURCE
VCC
I
CC
T
SENSOR
ADJUSTABLE
AMPLIFIER
OFFSET
CANCELLATION
SMART
COMPARATOR
SWITCHABLE
CURRENT
SOURCE
14 mA
V-
Fc = 0 Hz
7 mA
t
p
DIGITAL CONTROL UNIT
ON-CHIP
OSCILLATOR
mbl238
mra960
The MR sensor signal is fed into the conditioning IC. The offset, gain and
hysteresis are digitally adapted to ensure an exceptional air gap capability.
MR sensors offer a uniquely versatile combination of features
and important cost benefits. Based on the MR effect,
specifically designed sensors for angle and linear displacement
measurements are also available from NXP, as are solutions for
weak field detection.
NXP sensors are based on the MR effect, where the resistance
of a current-carrying magnetic material, for example a permalloy
I
mlc127
R = R
0
Permalloy
H
R
0
cos
2
M
ag
ne
tiz
at
io
n
Current
The magnetoresistive effect in permalloy
(19% Fe, 81% Ni) changes under the influence of an external
magnetic field. If an external field is applied, in the plane of the
current flow, the internal magnetization vector will rotate by the
angle of this field, changing the resistance of the material.
The MR sensor consists of four sensitive resistors in a
Wheatstone bridge configuration, with each resistor arranged
to maximize sensitivity and minimize temperature influences.
Such a Wheatstone bridge design along with the inherent
benefits of MR technology provides several advantages:
Ñ
reduction of temperature drift
Ñ
independent of mechanical assembly tolerances / shifts
Ñ
maximum signal output
Ñ
reduction of non-linearity
Tipical sensor bridge structure
www.nxp.com
NXP Semiconductors is in the process of being established as a separate legal entity in various countries worldwide. This process will be finalized in the course of 2006.
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