LG -A100 Service Manual page 27

3. TECHNICAL BRIEF
Figure 3.2.4 How sysclock Enable is Routed in the PMU
3.2.7 Sysclock Switching
The PMU controls the rf_sysclk_en signal of the DCXO in the RF macro. During startup the PMU enables the
DCXO. After the system is running the DCXO is controlled by the SCU of the baseband by using the
vcxo_enable signal. This is handled by a dedicated logic in the PMU, see Figure 21. As long as
rf_sysclk_en_pmu, the output of the PMU state-machine is high, vcxo_enable controls the rf_sysclk_en signal
to the RF. If rf_sysclk_en_pmu is low, the DXCO is switched off, independent from vcxo_enable.
3.2.8 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)
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