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 52 compares the settling times of different filter orders.

Sincfast is a modified sinc² filter whose transfer function follows Equation 3.

Equation 3.

Figure 51. Measured Effective Number Of Bits Versus Oversampling Ratio

Figure 52. 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 52.