LG -T500 Service Manual page 30

3. TECHNICAL BRIEF
Figure 3.4.2 How sysclock Enable is Routed in the PMU
3.2.9 Undervoltage Shutdown
In active mode the PMU periodically measures the battery voltage using the ADC from the charger unit. If the
battery is measured to be below the programmable shut-down level (called SYSOFF), the system changes to
OFF mode. This is done via the SHUTDOWN state of the PMU state machine. (see chapter switch OFF)
3.2.10 Software Reset
A software reset does not affect any PMU register. The PMU register are reset with the reset_pmufsm_n_o
signal. That means all PMU register are reset in OFF state. For details about the SW reset see chapter External
Reset Handling .
3.2.11 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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