Nokia RM-761 Service Manual page 132

RM-761; RM-799; RM-800
System Module
Figure 49 Power up timing and system sleep
Where the system after VBAT is applied goes first into the system OFF state. Connection of a valid battery
voltage (VBAT > 3.2V) will initiate a system startup, other valid system startup causes are pressing the ON
key, connection of a USB cable or charger, or a RTC alarm event.
When the system is in OFF state, only VRTC and VPMU are activated, with the common reference generated
by the low power band-gap reference LPBG. Upon detection of a valid turn-on event, first the high precision
band-gap reference is turned on, then the 1.8V step-down converter SD1 and the VCORE LDO are turned on
controlled by the PMU HW state-machine. The control signal RF_SYSCLK_EN is asserted to power up the DCXO
regulator in the RF macro, and after the DCXO has stabilized, the 26MHz system clock is available. The RESETX
signal is released 16ms after assertion of RF_SYSCLK_EN.
When RESETX is released, activation and control of the remaining supplies is done by SW, hence no exact
timing figures can be given here. The SW will, as one of the first actions, enable the 32 kHz oscillator and
enable the digital SLEEPCLK output, and turn on the 2.85V VAUX regulator. Control of remaining supplies (VSIM,
VMMC, VUSB, RF supplies) is handled by the respective SW drivers.
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