LG -T370 Service Manual page 31

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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

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)

LGE Internal Use Only

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Only for training and service purposes

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Troubleshooting