KMA199 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2011. All rights reserved.
Product data sheet Rev. 2 — 7 December 2011 4 of 36
NXP Semiconductors
KMA199
Programmable angle sensor
5. Functional description
The KMA199 amplifies two orthogonal differential signals which are delivered by MR
sensor bridges and converts them into the digital domain. The angle is calculated using
the COordinate Rotation DIgital Computer (CORDIC) algorithm. After a digital-to-analog
conversion the analog signal is provided to the output. Thus, the output is a linear
representation of the angular value. Zero angle, clamping voltages and angular range are
programmable. In addition, two 16-bit registers are available for customer purposes, like
sample identification.
The KMA199 comprises a Cyclic Redundancy Check (CRC) and an Error Detection and
Correction (EDC) supervision, as well as a magnet-loss detection to ensure a fail-safe
operation. A power-loss detection circuit pulls the analog output to the remaining supply
line, if either the supply voltage or the ground line is interrupted.
After multiplexing the two MR Wheatstone bridge signals and their successive
amplification, the signal is converted into the digital domain by an Analog-to-Digital
Converter (ADC). Further processing is done within an on-chip state machine. This
includes offset cancellation, calculation of the mechanical angle using the CORDIC
algorithm, as well as zero angle and angular range adjustment. The internal
Digital-to-Analog Converter (DAC) and the analog output stage are used for conversion of
the angle information into an analog output voltage, which is ratiometric to the supply
voltage.
The configuration parameters are stored in an user-programmable EEPROM. The OWI
(accessible using pin OUT/DATA) is used for accessing the memory.
5.1 Angular measurement directions
The differential signals of the MR sensor bridges depend only on the direction of the
external magnetic field strength H
ext
, which is applied parallel to the plane of the sensor.
In order to obtain a correct output signal, the minimum saturation field strength has to be
exceeded.
