User’s Manual 9 Rev. 1.0
2019-04-29
TLE5501
TMR-Based Angle Sensor
Transient behavior
For the time τ
s
until the voltage settles to a value less than 0.5LSB from final value U
0
the following relation
holds:
(2.7)
For a 12 bit ADC with N = 12, τ
s
becomes τ
s
= 9.0τ
br
.
This means that a waiting time of approx. 9 times of τ
br
should be considered for settling the signal before it
can be converted with the ADC.
2.2 Recommendation for the external capacitor C
b
For most applications, it is a target to achieve a high angle accuracy. To reach this, the phase shift Φ between
the magnetic input signal and the bridge output shall be small. It can be estimated using Equation (2.3).
The external buffer capacitor C
b
can be calculated depending on magnetic input frequency f
in
and desired
phase shift Φ according to Equation (2.8):
(2.8)
For an application with 8000rpm, f
in
= 133Hz, R = 4kOhm (R = R
TMR
/2, see Chapter 2.1) and Φ = 0.2° the
maximum buffer capacitor C
b
is calculated to C
b
= 1nF.
The time constant τ
br
of the bridge in this case is τ
br
= R
TMR
/2 x C
b
= 4kOhm x 1nF = 4µs.
So the settling time of the bridge τ
s
is then τ
s
= 9τ
br
= 36µs.
For applications with higher speed, the buffer capacitor C
b
can be further reduced but it has to be taken into
account, that there is also a capacitive load of the ADC of the microcontroller which needs to be charged.
Further details in Chapter 3.
τ
s
τ
b
r
0.5
2
N
-------
èø
æö
ln⋅
èø
æö
–=
C
b
Φ()tan
2πRf
in
-----------------
=
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