SPRUII0F May 2019 – June 2024 TMS320F28384D , TMS320F28384D-Q1 , TMS320F28384S , TMS320F28384S-Q1 , TMS320F28386D , TMS320F28386D-Q1 , TMS320F28386S , TMS320F28386S-Q1 , TMS320F28388D , TMS320F28388S
Most control systems require protection of the system by tripping the PWM in case the current or voltage goes out of bounds. The primary purpose of the secondary (comparator) filter is to allow the user to monitor input conditions with a fast settling time. This allows the user to trip PWMs to protect the system from potential damage.
The comparator filter is a configurable Sinc filter that supports the following filter types: Sinc1, Sinc2, Sinc3, and SincFast. The comparator OSR (COSR) settings can be configured from 1 to 32 and is independent of the data filter. Effective resolution of the comparator filter (ENOB) depends upon the comparator filter type, COSR, and sigma-delta modulator frequency. By default, the comparator filter is disabled and setting SDCPARMx.CEN = 1 enables the comparator filter. The comparator filter output is represented in 16-bit unsigned format. This filter unit translates a low input signal as 0 and a high input signal as 1. The resulting calculations give only positive values for the output of the comparator filter. Table 28-7 shows the different full-scale values that the comparator filter can store using different OSRs.
OSR | Sinc1 | Sinc2 | Sinc3 | SincFast |
---|---|---|---|---|
x | 0 to x | 0 to x2 | 0 to x3 | 0 to 2x2 |
4 | 0 to 4 | 0 to 16 | 0 to 64 | 0 to 32 |
8 | 0 to 8 | 0 to 64 | 0 to 512 | 0 to 128 |
16 | 0 to 16 | 0 to 256 | 0 to 4096 | 0 to 512 |
32 | 0 to 32 | 0 to 1024 | 0 to 32,768 | 0 to 2048 |
See Section 28.6.1 to understand how to calculate data rate and latency of comparator filter.
The output of the comparator filter is memory-mapped and can be read in the SDCDATAx register. This register, SDCDATAx, is updated every COSR number of SD-Cx cycles. The comparator filter digital output is connected to digital comparators explained below.