Determination Of Sensitivity Polynomial From Measurement - Infineon TLE4997 User Manual

5.3

Determination of Sensitivity Polynomial from Measurement

For the determination of the Coefficients for the application sensitivity polynomial
of the temperature behavior of the sensor output in the application is recommended. A basic example for a position
sensing application using the TLE4997 and a moveable permanent magnet is shown in
In a setup that uses a permanent magnet, the magnetic field has a temperature dependency due to the thermal
reduction of the remanence. In order to determine the optimum sensitivity compensation behavior of the sensor in
to cancel this temperature dependency, the sensor's output value shall be measured at different temperatures,
with the permanent magnet in a fixed position.
As the thermal reduction of the remanence depends mainly on the magnetic material used and has typically only
minor variations from sample to sample, a reference measurement on a number of application samples is typically
sufficient to determine a reference polynomial for the application in general, which is to be used for production. It
is typically not required to perform the described measurement over temperature for every individual sample.
TLE4997
Figure 5-2 Example Position Sensing Application
With the described setup, the following procedure is used to obtain the coefficients of the application sensitivity
polynomial:
• Measure the sensor output for at least three different temperatures at a defined, fixed magnet position. The
magnetic flux densitiy at the sensor shall be non-zero at this given magnet position. It is recommended for best
accuracy of the calibration procedure to use a magnet position that leads to the highest possible magnetic flux
at the sensor, while still being inside the configured magnetic flux range (± 50 mT, ±100 mT, or ±200 mT).
• For each data point, read the junction Temperature T
• For each data point, calculate the compensation sensitivity value S
value at zero field VDAC
VDAC
i ( )
------------------------------------------------ -
S
=
i ( )
VDAC VDAC
–
(i)
• Plot S as a function of T
Figure 5-3).
User's Manual
B(T)
, using Equation (5.7)
0
0
0
(i)
and apply a quadratic fit (cx
J
Calibration of TLE4997 Temperature Compensation
Movement
N S
(i)
, and the VDAC
J
(i)
from the VDAC
2
+ bx + a) which yields coefficients a, b and c (See
27
User's Manual
(Equation (5.3)) a measurement
Figure 5-2.
(i)
value via the programming interface.
(i)
value and the output
v01_01, 2019-08
TLE4997
(5.7)