NXP Semiconductors Kinetis KE1xZ256, Reference Manual

Page: 809 / 1325

37.9.1 Initialization
A typical startup sequence is as follows.
The time required to stabilize COUT is the power-on delay of the comparators plus the
largest propagation delay from a selected analog source through the analog comparator,
windowing function, and filter. See the datasheet for power-on delays of the comparators.
The windowing function has a maximum of one bus clock period delay. The filter delay
is specified in the
Low-pass filter section.
During operation, the propagation delay of the selected data paths must always be
considered. It may take many bus clock cycles for COUT and C0[CFR]/C0[CFF] to
reflect an input change or a configuration change to one of the components involved in
the data path.
When programmed for filtering modes, COUT initially equals 0 until sufficient clock
cycles have elapsed to fill all stages of the filter. This occurs even if COUTA is at a logic
1.
37.9.2 Low-pass filter
The low-pass filter operates on the unfiltered and unsynchronized and optionally inverted
comparator output COUTA and generates the filtered and synchronized output COUT.
Both COUTA and COUT can be configured as module outputs and are used for different
purposes within the system.
Synchronization and edge detection are always used to determine status register bit
values. They also apply to COUT for all sampling and windowed modes. Filtering can be
performed using an internal timebase defined by FPR[FILT_PER], or using an external
SAMPLE input to determine sample time.
The need for digital filtering and the amount of filtering is dependent on user
requirements. Filtering can become more useful in the absence of an external hysteresis
circuit. Without external hysteresis, high-frequency oscillations can be generated at
COUTA when the selected INM and INP input voltages differ by less than the offset
voltage of the differential comparator.
37.9.2.1 Enabling filter modes
Filter modes can be enabled by:
Chapter 37 Comparator (CMP)
Kinetis KE1xZ256 Sub-Family Reference Manual, Rev. 3, 07/2018
NXP Semiconductors 809