TLE5009-E2000 Datasheet, PDF (26/32 Pages) Infineon Technologies AG – GMR-Based Angular Sensor

3.5
Safety Features
TLE5009
Specification
3.5.1 Built in error diagnosis
The device sensor provides two functions at the V_GMR pin. During normal operation the voltage measured at this
pin is temperature dependent. The typical voltage at room temperature and the temperature coefficient are given
in Table 4 “Electrical parameters” on Page 15.
The second purpose of pin V_GMR is the diagnosis functionality. In case the device detects an internal error, the pin
is driven to a low level as described in Table 4 “Electrical parameters” on Page 15.
The errors that can be detected by monitoring the status of the V_GMR pin are:
• Start-up failure
• Overvoltage at VDD (threshold level min. 6V, max. 7V)
• Undervoltage at internal nodes
3.5.2 External Diagnosis
Adressing the demands for functional safety, run time checks can be done to increase the diagnostic coverage.
Depending on the application specifics such as the available time and processing capabilities, the sensor
behaviour is monitored and compared with the specified behaviour of the device.
3.5.2.1 Vector length check differential voltage mode
A comprehensive safety check is to monitor the vector length of Vx and Vy signals. Output signals representing
sine and cosine have a fixed 90° phase relationship to each other. To determine if the output signals are valid, the
length of the output vector length must be nearly constant independent of the magnet position.
The vector length corresponds to the amplitude of the output signals and utilizes the fact that there is a 90° phase
shift between sine and cosine output. It is calculated according to Equation (26).
As illustrated in Figure 14 “Valid vector length”, the vector describes a circle along one revolution of the magnet.
The length of the vector is almost constant, slightly influenced by GMR synchronicity, orthogonality, offset and
temperature.
V_VEC =
V + V 2
X _ DIFF
2
Y _ DIFF
(26)
VY (SIN)
VVEC
VX
VY
VX (COS)
Figure 14 Valid vector length
Data Sheet
26
Rev. 1.1, 2012-04