Rotational speed sensor Constantly aware of that speed sensation 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 Ñ ABS Ñ Engine management Ñ Gearbox Ñ Transmission systems Ñ Vehicle speed Ñ 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. 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 MR-sensor Extra thick leadframe material for robustness, bendable Conditioning IC Conditioning IC Component detail of the KMI20 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 magnetic field lines direction of motion magnetic field lines S magnet magnetized target N sensor current (a) (b) (c) 14 mA (d) S V t sensor amplifier, comparator 7 mA position N MBE073 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 L arge (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 KMIXY/1 mbh778 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/4 mbh779 KMIXY/2 mbh777 KMI15 – 7/14 mA current output (2-wire) KMI18 – open collector output (3-wire) CONSTANT CURRENT SOURCE SENSOR SENSOR AMPLIFIER SCHMITT TRIGGER SWITCHABLE CURRENT SOURCE VCC VOLTAGE CONTROL VCC VOLTAGE CONTROL SCHMITT TRIGGER AMPLIFIER Vout open collector output VGND 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 ICC T SENSOR ADJUSTABLE AMPLIFIER OFFSET CANCELLATION SMART COMPARATOR SWITCHABLE CURRENT SOURCE 14 mA V- Fc = 0 Hz 7 mA tp DIGITAL CONTROL UNIT ON-CHIP OSCILLATOR mra960 mbl238 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. 7/14 mA output signal as a function of time Product overview Sensor type typ. sensing distance (mm) Tooth frequency (Hz) Target Interface Magnet size (mm) KMI15/1 0.9 - 2.9 0 - 25.000 note 1 Current 8 x 8 x 4.5 KMI15/2 0.5 - 2.7 0 - 25.000 note 2 Current 3.8 x 2 x 0.8 KMI15/4 0.5 - 2.3 0 - 25.000 note 1 Current 5.5 x 5.5 x 3 KMI18/1 0.9 - 2.9 0 - 25.000 note 1 Open collector 8 x 8 x 4.5 KMI18/2 0.5 - 2.7 0 - 25.000 note 2 Open collector 3.8 x 2 x 0.8 KMI18/4 0.5 - 2.3 0 - 25.000 note 1 Open collector 5.5 x 5.5 x 3 KMI20/1 0.9 - 3.5* 0 - 2.500 note 1 Current 8 x 8 x 4.5 KMI20/2 0.5 - 3.2* 0 - 2.500 note 2 Current 3.8 x 2 x 0.8 KMI20/4 0.5 - 2.8* 0 - 2.500 note 1 Current 5.5 x 5.5 x 3 * + 1 mm dynamic reserve | note 1 - ferrous target | note 2 - magnetized target Advantages by design 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. R = R0 $ R0 cos2 A M ag ne tiz H at io n Permalloy A Current I mlc127 The magnetoresistive effect in permalloy NXP sensors are based on the MR effect, where the resistance of a current-carrying magnetic material, for example a 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. © 2006 Koninklijke Philips Electronics N.V. All rights reserved. Reproduction in whole or in part is prohibited without the prior written consent of the copyright owner. The Date of release: September 2006 information presented in this document does not form part of any quotation or contract, is believed to be accurate and reliable Document order number: 9397 750 15731 and may be changed without notice. No liability will be accepted by the publisher for any consequence of its use. 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