NXP Semiconductors K22F series, Reference Manual, Page: 591 / 1407

27.3 External Crystal Connections
The connections with a crystal is shown in the following figure. External load capacitors
and feedback resistor are not required.
RTC Oscillator Module
EXTAL32
Crystal or Resonator
XTAL32 V
SS
Figure 27-2. Crystal Connections
27.4 Memory Map/Register Descriptions
RTC oscillator control bits are part of the RTC registers. Refer to RTC Control Register
(RTC_CR) , or RTC_GP_DATA_REG in the chip-specific information section, for more
details.
27.5 Functional Description
As shown in Figure 27-1 , the module includes an amplifier which supplies the negative
resistor for the RTC oscillator. The gain of the amplifier is controlled by the amplitude
detector, which optimizes the power consumption. A schmitt trigger is used to translate
the sine-wave generated by this oscillator to a pulse clock out, which is a reference clock
for the RTC digital core.
The oscillator includes an internal feedback resistor of approximately 100 MΩ between
EXTAL32 and XTAL32.
In addition, there are two programmable capacitors with this oscillator, which can be
used as the Cload of the oscillator. The programmable range is from 0pF to 30pF.
Chapter 27 RTC Oscillator (OSC32K)
K22F Sub-Family Reference Manual, Rev. 4, 08/2016
NXP Semiconductors 591