SPRUHX5I August 2014 – May 2024 TMS320F28374S , TMS320F28375S , TMS320F28375S-Q1 , TMS320F28376S , TMS320F28377S , TMS320F28377S-Q1 , TMS320F28378S , TMS320F28379S
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 enabled. 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 13-6 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 13.4.1 to understand how to calculate data rate and latency of comparator filter.
The output of the comparator filter is not memory-mapped; instead the output is connected to digital comparators explained below.