Infineon TLE5501 E0001, Руководство пользователя

Страница: 13 / 19

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 8k
Ω.
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
Δ
U 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_
ro
ta
ti
o
n
(rp
m
)
f_s
a
mp
le
(
k
H
z)
C
b
(nF)
f_sample
f_rotation
Cb 2
N 1 +
1 –
( )
CSH
⋅ >