FlexPWM RM0046
674/936 Doc ID 16912 Rev 5
Input filter considerations
The FILT_PER value should be set such that the sampling period is larger than the period of
the expected noise. This way a noise spike will only corrupt one sample. The FILT_CNT
value should be chosen to reduce the probability of noisy samples causing an incorrect
transition to be recognized. The probability of an incorrect transition is defined as the
probability of an incorrect sample raised to the FILT_CNT+3 power.
The values of FILT_PER and FILT_CNT must also be traded off against the desire for
minimal latency in recognizing input transitions. Turning on the input filter (setting FILT_PER
to a non-zero value) introduces a latency of ((FILT_CNT+4) x FILT_PER x IPBus clock
period). Note that even when the filter is enabled, there is a combinational path to disable
the PWM outputs. This is to ensure rapid response to fault conditions and also to ensure
fault response if the PWM module loses its clock. The latency induced by the filter will be
seen in the time to set the FFLAG and FFPIN bits of the FSTS register.
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