User Manual

Apollo3 Blue Datasheet
DS-A3-0p9p1 Page 524 of 909 2019 Ambiq Micro, Inc.
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software intervention, so that software does not need to manage any enabling or disabling of the
oscillators. As an example, an I
2
C/SPI Master requires the HFRC in order to generate the serial interface
clock. If a transfer is initiated and the processor is put into Deep Sleep mode, the HFRC will remain active
until the I/O transfer is completed. At that point the HFRC will be powered down without requiring any
software intervention.
Figure 64 shows the available clock sources, divisors and distribution to the various modules of the
Apollo3 Blue MCU.
Figure 64. Apollo3 Blue Clock Tree
12.1.2 Low Frequency RC Oscillator (LFRC)
The low power LFRC, with a nominal frequency of 1024 Hz, is used when short term frequency accuracy is
not important. It also supplies clocks for SIMO buck regulator in low power mode (32kHz) as well as some
basic state machines and is always enabled. Calibration logic is included.