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LGE Internal Use Only Copyright © 2010 LG Electronics. Inc. All right reserved.
Only for training and service purposes
3. TECHNICAL BRIEF
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3. TECHNICAL BRIEF
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.
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 .