3. TECHNICAL BRIEF
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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.