AMC1204_15 Datasheet, PDF (23/37 Pages) Texas Instruments – AMC1204 20-MHz, Second-Order, Isolated Delta-Sigma Modulator

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AMC1204, AMC1204B
SBAS512E – APRIL 2011 – REVISED SEPTEMBER 2015
Typical Application (continued)
8.2.1.3 Application Curves
In motor control applications, a very fast response time for overcurrent detection is required. The time for fully
settling the filter in case of a step-signal at the input of the modulator depends on its order; that is, a sinc³ filter
requires three data updates for full settling (with f_DATA = f_CLK / OSR). Therefore, for overcurrent protection, filter
types other than sinc³ might be better choices. An alternative is, for example, the sinc² filter. Figure 50 compares
the settling times of different filter orders.
Sincfast is a modified sinc² filter whose transfer function follows Equation 3.
2
H(z) =
1 - z^-OSR
1 - z^-1
(1
+
z ) ^-2OSR
(3)
16
14
12
10
8
6
4
2
0
1
sinc³
sincfast
sinc²
sinc¹
10
100
OSR
1000
16
14
sinc³
sincfast
12
10
sinc²
8
6
sinc¹
4
2
0
0 1 2 3 4 5 6 7 8 9 10 11 12 13
Settling Time (ms)
Figure 49. Measured Effective Number Of Bits Versus
Oversampling Ratio
Figure 50. Measured Effective Number of Bits Versus
Settling Time
In the case of a continuous signal fed into a sinc filter, the time delay for such signal corresponds to half of the
settling time shown in Figure 50.
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