LG -A100 Service Manual page 28

3. TECHNICAL BRIEF
3.2.9 Silent Reset
WDT-reset and software-reset shall happen silently to ending customer: SIM card and interfaces have to stay
powered and not reset by neither WDT-reset or C166s SRST instruction. To allow this, some LDO settings and
some registers (as e.g. USIM_pad control register) are reset only by system-reset (HW-reset or power-on reset)
Figure 3.2.5 PMU Reset
3.2.10 PMU Clock
During the first startup (for example plugging in a battery) a PMU internal oscillator is used for generation of
the PMU clock (pmu_clock). The frequency is slightly above 32 kHz (typ. 50 kHz) to be out of the audio band
also for worst case devices. After first startup the software shall enable the 32 kHz crystal oscillator. It is not
possible to use the 32 kHz oscillator during first startup, because the settling time of the oscillator can be
quite long. After the 32 kHz oscillator is running and settled the software shall switch the PMU clock to the 32
kHz clock and disable the internal PMU oscillator for power saving reasons. The 32 kHz oscillator shall never
be disabled after the PMU clock has been switched. The ADC in the charger unit has it's own oscillator
generating a frequency of about 10 MHz. This oscillator is running during charging and during battery
measurements triggered by the PMU. It is off otherwise.
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