Table 28-3. Oscillator modes (continued)Mode Frequency RangeHigh-frequency mode1, high-gain fosc_hi_1 (3 MHz) up to fosc_hi_1 (8 MHz)High-frequency mode1, low-powerHigh-frequency mode2, high-gain fosc_hi_2 (8 MHz) up to fosc_hi_2 (32 MHz)High-frequency mode2, low-powerNOTEFor information about low power modes of operation used inthis chip and their alignment with some OSC modes, see thechip's Power Management details.28.9.2.1 Low-Frequency, High-Gain ModeIn Low-frequency, high-gain mode, the oscillator uses a simple inverter-style amplifier.The gain is set to achieve rail-to-rail oscillation amplitudes.The oscillator input buffer in this mode is single-ended. It provides low pass frequencyfiltering as well as hysteresis for voltage filtering and converts the output to logic levels.In this mode, the internal capacitors could be used.28.9.2.2 Low-Frequency, Low-Power ModeIn low-frequency, low-power mode, the oscillator uses a gain control loop to minimizepower consumption. As the oscillation amplitude increases, the amplifier current isreduced. This continues until a desired amplitude is achieved at steady-state. This modeprovides low pass frequency filtering as well as hysteresis for voltage filtering andconverts the output to logic levels. In this mode, the internal capacitors could be used, theinternal feedback resistor is connected, and no external resistor should be used.In this mode, the amplifier inputs, gain-control input, and input buffer input are allcapacitively coupled for leakage tolerance (not sensitive to the DC level of EXTAL).Also in this mode, all external components except for the resonator itself are integrated,which includes the load capacitors and feeback resistor that biases EXTAL.Functional DescriptionKL27 Sub-Family Reference Manual , Rev. 5, 01/2016452 Freescale Semiconductor, Inc.
