User’s Manual 8 Rev. 1.0
2019-04-29
TLE5501
TMR-Based Angle Sensor
Transient behavior
For a bridge resistivity of R
TMR
= 8kΩ and a buffer capacitor of C
b
= 1nF, the cut-off frequency f
c
is calculated
according to Equation (2.4) with R = R
TMR
/2.
(2.4)
Care should be taken, that the buffer capacitor C
b
is chosen in a way that the phase shift between output signal
and input signal does not impact the angle accuracy for the maximum given frequency in the application.
For example, to have the phase shift Φ below 0.2° with a C
b
= 1nF, the maximum frequency f
rotation
in the
application is estimated according Equation (2.5) to be below 139Hz = 8340rpm.
(2.5)
As the TLE5501 is a passive sensor with analog output, also further capacitive load, coming e.g. from the ADC
input of the microcontroller has to be considered. Further details to that are given in Chapter 3. The operation
of the TLE5501 should always be well below the calculated cut-off frequency f
c
with the total capacitive load
considered (buffer capacitor C
b
, ADC input capacity, parasitics) and assuming a worst case bridge resistivity
R
TMR
according to the datasheet. Depending on the accuracy requirements of the application, it might be
necessary to further reduce the input magnetic frequency to minimize the phase shift between input and
output signal to the required value.
Settling time τ
s
of a RC filter
Assuming an ADC with N bits resolution, which is used to measure the bridge output signal, it is desired that
the measurement error of the output voltage is less than 0.5LSB.
To achieve this, the input frequency has to be low compared to the cut-off frequency f
c
(Equation (2.4)), given
by the RC time constant τ
br
of the bridge resistivity and the external capacitor.
Using Equation (2.1), the following relation can be obtained for the time until the voltage reaches U
0
with a
deviation of less than 0.5LSB:
(2.6)
f
c
1
2πRC
---------------
1
πR
TMR
C
--------------------------
39.78kHz== =
f
Φ()tan
2πRC
-----------------
=
Ut() U
0
1e–
t τ⁄–
()⋅ U
0
1
0.5
2
N
-------
–
èø
æö
⋅==
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