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TLE4997
User's Manual
Calibration of TLE4997 Output Characteristic
6.2.2
Calibration without Application Readout
In case a readout of the sensor before calibration is not desired, the sensor can be roughly calibrated just from a
knowledge of the minimum and maximum magnetic flux values that occur in the application. In this case, the
calibration cannot compensate any variation of parameters due to production spread of sensor IC or application
module. The offset and gain are calculated only based on the minimum and maximum magnetic field in the
application.
Example
An example application has a minimum magnetic flux of B
= -25 mT and a maximum magnetic flux of B
= 75
min
max
mT, which needs to be mapped to 4.5V and 0.5V, the clamping levels must be set to 4.7V and 0.3V.
The precalibrated gain value is 1.62 and the precalibrated offset value is 50% (sensor read-out).
The +/- 100mT default range is well suited, as both magnetic flux values are well within the allowed range.
The sensitivity needs to be set in that way that the magnetic flux change from B
= -25mT to B
= +75mT results
2
1
in a voltage change from V
= 0.5V to V
= 4.5V.
out2
out1
So the required sensitivity is (V
- V
)/(B
- B
) = (4.5-0.5) / (+75-(-25)) = 0.04 V/mT = 40mV/mT.
out1
out2
1
2
As the default sensitivity is about 60mV/mT, the gain value needs to be lowered by a factor of (40 / 60) = 0.667.
So the gain must be reprogrammed to (1.62 x 0.667) = 1.08.
For the offset setup, we can proceed as follows:
A magnetic flux of 75mT will cause with the new sensitivity value of 40mV/mT a output change of (75 x 40) = 3000
mV = 3V.
With the default offset setup of 2.5V we would see on the output (only theoretically) 5.5V, but we need 4.5V. So
the offset value needs to be lowered by (5.5-4.5) = 1V.
This corresponds to an ratiometric percentage of (1/5) x 100% = 20%. So it is necessary to set the new offset to
(50 - 20) = 30 %.
The clamping parameters need to be set to (0.3 / 5) x 100% = 6% and (4.7 / 5) x 100% = 94% to provide the
required output limits.
User's Manual
36
v01_01, 2019-08
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