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KMA200,115

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KMA200 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2011. All rights reserved.
Product data sheet Rev. 8 — 7 December 2011 4 of 33
NXP Semiconductors
KMA200
Programmable angle sensor
5. Functional description
The KMA200 amplifies two orthogonal sinusoidal signals delivered by the MR-sensor
element and converts them into the digital domain. Using the COordinate Rotation DIgital
Computer (CORDIC) algorithm, the angle is calculated. Angle output is either analog or
digital. The KMA200 comprises diagnostic features that ensure a complete online
supervision of all essential functional blocks including verification of input and output
signals and temperature supervision. In addition, the circuit is protected against reverse
polarity, overvoltage and short circuit at all external pins.
Two instrumentation amplifiers and -modulators convert the amplified signals into two
high-speed digital bit streams. The bit streams are filtered and decimated by two digital
decimation filters to obtain digital signals with higher resolution at a lower speed.
Further processing is done within an on-chip calibration microcontroller. This includes
offset cancellation, calculation of the mechanical angle using the CORDIC algorithm,
zero-angle and angular-range adjustment.
In addition, the calibration microcontroller performs diagnostic tasks to ensure the validity
of its results. The calibration microcontroller takes calibration constants from an on-chip
EEPROM and stores intermediate results in a Random Access Memory (RAM). The
calculated angle is given out either digitally with an SPI-compatible serial interface or
analog via the analog output stage. Several output characteristics can be selected.
In case of analog output the analog output stage is used for conversion of the angle
information into two analog output voltages ratiometric to the supply voltages. For this
purpose, the analog output stage contains two resistor-string Digital-to-Analog Converters
(DACs) which share the same resistor string. The two analog output voltages are buffered
by two offset-compensated amplifiers.
The internal circuitry is protected against overvoltage with special protection circuits.
Protection against reverse polarity is realized with the help of a current limiting circuit.
In addition, there are various support circuits like bias generators, a free-running oscillator
including an oscillator fail-safe circuit and a power-on reset circuit which generates a reset
in dependence of the supply voltage.
KMA200 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2011. All rights reserved.
Product data sheet Rev. 8 — 7 December 2011 5 of 33
NXP Semiconductors
KMA200
Programmable angle sensor
6. Diagnostic features
The KMA200 includes diagnostic features to ensure the validity of its output signals. The
diagnostic features can be configured with the control information words (ctrl) written to
the user-programmable EEPROM.
In the analog output modes a diagnostic error condition is signaled to the user by setting
the outputs into the high-impedance state. The outputs are forced to lie in the upper or
lower diagnostic range by external pull-up or pull-down resistors.
With no external pull-up/pull-down resistors the output signal will be internally pulled up to
upper diagnosis range.
If digital output is selected, an error condition can also be signaled by setting the error flag
in the digital output word. The least significant bits show the error code. The Table 4
shows the behavior in detail:
Once a diagnostic error condition is reached, the KMA200 continues to work normally
after a new external power-on reset or by itself, as described in the table below. It is
possible to configure the KMA200 the way that the error condition has to be fulfilled more
than once. The number of error conditions that is necessary can also be programmed with
bits in the control information words.
[1] Reactivation for angular measurement with valid angle information (normal operation mode) only by new
external power-on reset
Temperature supervision
The chip temperature measured within the KMA200 can be used to detect
over-temperature conditions. Two temperature levels are defined: the temperature
warning level and the temperature shutdown level.
The user can evaluate the temperature warning if digital output mode is selected. When
the device temperature exceeds the warning level, the error flag in the digital output word
is set. The other data bits still show the angle information. In the analog output modes, the
device temperature warning is not available. If the temperature exceeds the
over-temperature shutdown level, the KMA200 switches off.
Table 4. Summary KMA200 behavior at diagnosis conditions in normal operation mode
Error appearance Analog output Digital output
Oscillator fail detection
[1]
high-impedance state
[1]
high-impedance state
Cyclic Redundancy Check (CRC)
[1]
high-impedance state
[1]
diagnosis bit set
Watchdog
[1]
high-impedance state
[1]
high-impedance state
Input stage (including magnet lost) high-impedance state diagnosis bit set
Output stage
[1]
high-impedance state -
Over-temperature warning - diagnosis bit set
Over-temperature shutdown
[1]
high-impedance state
[1]
high-impedance state
Overvoltage high-impedance state high-impedance state
Reverse polarity high-impedance state high-impedance state
KMA200 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2011. All rights reserved.
Product data sheet Rev. 8 — 7 December 2011 6 of 33
NXP Semiconductors
KMA200
Programmable angle sensor
Diagnosis of input stage
For diagnosis of the input stage, the calibration microcontroller calculates the expected
signal magnitude using the temperature information and the EEPROM constants and
compares it to the signal magnitude based on the current measurement.
If the difference of the two magnitudes is greater than an allowed deviation, an error
condition is signaled to the user.
The allowed difference depends on the bits DI1 and DI0 in the EEPROM control
information word.
Diagnosis of output stage
Both analog outputs are supervised by the auxiliary ADC which reads the present analog
signal and converts it back to the digital domain with a resolution of 8 bits. The digitized
value is compared to the digital angle value originally sent.
If the difference of these two values is greater than an error bound, an error condition is
signaled by switching off the analog outputs.
The allowed difference depends on the bits DO1 and DO0 in the EEPROM control
information word.
CRC check of EEPROM constants
During normal operation mode a CRC code of the configuration constants taken from the
EEPROM is calculated on a regular basis. This code is compared to a pre-calculated CRC
code from the EEPROM (CRC). If there is a mismatch, an error condition is signaled to
the user by setting the error flag in the digital output word or by switching off the analog
outputs.
The CRC code used is the CRC-16 code (ISO/IEC 3309:1993 and ITU-T V.42)
Watchdog timer
The KMA200 comprises a watchdog timer to supervise the flow of the program. After
reset, the watchdog is automatically activated. During operation the watchdog timer must
be toggled on a regular basis, as otherwise the error condition is signaled. The access to
the watchdog timer is protected against unwanted operations using a fail-safe watchdog
feed sequence.
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KMA200,115

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NXP Semiconductors
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Motion & Position Sensors Board Mount Motion & Position Sensors SNSR MAGNETIC TAPE-7
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