User’s Manual 5 Rev. 1.0
2019-04-29
TLE5501
TMR-Based Angle Sensor
Transient behavior
2 Transient behavior
For the sine and cosine output pins, it is also recommended to use a buffer capacitor C
b
for filtering purpose.
As the device itself has a high output impedance, given by the TMR resistors R
TMR
, this buffer capacitor builds
a low-pass filter together with the bridge resistivity.
2.1 Bandwidth of the TMR bridge
It has to be taken into account that the low pass filter limits the bandwidth of the sensor and increases step
response time. Figure 5 shows a schematic of the sensor output structure with an external capacitor C
b
. The
resistivity of a TMR resistor R
TMR
is specified in the datasheet and has a value between 4kΩ and 8kΩ.
Figure 5 Schematic of one branch of the TMR bridge with external buffer capacitor C
b
The result of a pSPICE simulation of this output structure is shown in Figure 6. A resistor of R
TMR
= 8kΩ and a
capacitor value of C
b
= 1nF is assumed. Applying a voltage step of 5V on the supply V
DD
is simulated. This is
compared with analytical simulations using below Equation (2.1):
(2.1)
The time constant for the bridge τ
br
is defined as: τ
br
= RC, U
0
is taken to be 2.5V = VDD/2.
A good approximation of the transient behavior in the analytical calculation can be achieved with R = 4kΩ and
C
b
= 1nF, so R in the analytical simulation is half of the resistivity of one TMR resistor R
TMR
of the bridge.
This behavior is equal to a low-pass filter at the sensor output with R = R
TMR
/2 and C
b
.
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