LG -T510 Service Manual page 31

3. TECHNICAL BRIEF
3.2.12 System Sleep Mode
The sleep mode is controlled by using the VCXO_enable signal. This signal is used to switch the LDO's and the
DC/DC converter SD1 in a programmable way into its low power mode (PFM). In addition DC/DC converter
SD1 can be configured to change the output voltage to a lower value for additional power saving.
VCXO_enable is also used to deactivate the HPBG and setting LDO LPMU in the ultra-low-power mode. In
addition the DCXO is switched off by the VCXO_enable signal. The VCXO_enable signal is also used to switch
some LDO's (software configured) to sleep and/or off mode or to change the output voltages of said LDO's.
The state of the main PMU state machine is not changed due to VCXO_enable.
3.2.13 DC/DC Pre-Load Register Handling
The DC/DC converter works in different modes. If the mode is switched from PFM to PWM the pulse-width of
the DC/DC converter depends on the current battery voltage (and on the output voltage). The PMU state-
machine knows the battery voltage because of the battery supervision function. Depending on this value it
selects a startup pulse-width for the DC/DC converter out of a register table. (4-values)
3.2.14 Power Down Sequence
Setting bit OFF in the GeneralControl register switches the system into OFF mode. After the turn off event, the
state-machine switches to the SHUTDOWN state. The reset_pmu_n_o signal changes to low, the I/O pads are
isolated using the padisolation_n signal, the LCORE LDO and the SD1 DC/DC converter are switched off, the
LPMU LDO is switched to ultra-low power mode, the DCXO is turned off and the bandgap buffer is disabled.
Before switching OFF the software shall have enabled the 32 kHz oscillator and has switched the PMU clock to
the 32 kHz clock to archive the target OFF current .
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