User’s Manual 13 Rev. 1.0
2019-04-29
TLE5501
TMR-Based Angle Sensor
Connection to a micro controller
Figure 12 Sampling frequency f
sample
and sensor bandwidth f
rotation
as function of the buffer capacitor
C
b
. R
TMR
is assumed to be 8kΩ.
3.2.2 Load step reduction
As seen in Equation (3.1), the drop of the voltage at the start of the ADC sampling (closing of S/H switch) can
be reduced by increasing the value of C
b
. If this load step ΔU is less than 0.5 LSB, it is no longer visible and there
is no need for a dedicated waiting time until the signal settles. Using Equation (3.1) the following relation can
be obtained (N: bits of the ADC):
(3.3)
For a 12bit ADC and C
SH
= 7pF, the buffer capacitor C
b
has to be larger than 57.3nF. In this case, the voltage drop
during ADC sampling is less than 0.5 LSB and therefore not visible.
On the other side, such a large buffer capacitor limits the bandwidth of the sensor and the time constant of the
bridge calculates to τ
br
= 229.3µs. For the phase shift to be less than 0.2°, the maximum frequency of the
applied magnetic field f
rotation
has to be below 145rpm according to Equation (2.5).
In this approach, the sampling frequency can be increased but the bandwidth of the sensor is reduced at the
same time.
For a specific application, the best combination of required bandwidth, sampling frequency and sampling
accuracy has to be found and the buffer capacitor C
b
has to be selected accordingly.
100
1000
10000
100000
1
10
100
1,000
0.0 0.1 1.0 10.0 100.0
f_rotation (rpm)
f_sample (kHz)
C
b
(nF)
f_sample
f_rotation
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