Nokia 301 Service Manual page 147

RM-839; RM-840; RM-841
System Module
• Small digital state Machine (SM1)
• Main PMU state Machine (SM2)
Analog Start-up Circuit
To guarantee correct start-up of the baseband and RF sub-systems, an internal Power-On Reset (POR) signal
is needed. It is generated by combining a signal that validates the battery supply voltage (VBAT) and the VRTC
output voltage. The trigger values are VPOR_H (nominal 2.5 V) for the battery voltage and 1.8 V for the VRTC
voltage.
Small State-Machine (SM1)
Within the digital core of the PMU sub-system there are two main blocks: (1) the small state-machine (SM1)
and (2) the main state-machine (SM2). SM1 is always active and handles on-events. For optimal power
consumption, SM2 is isolated from the power supply using µ-switches when the PMU is in its OFF state. The
clock frequency of SM1 is 25 kHz (nominal) which originates from the internal 50 kHz analog oscillator(AOSC).
As response to a power-on event, SM1 enables the power domain of SM2 (main state-machine) and releases
the reset for SM2. At this point, SM2 completes the start-up sequence.
Main State-Machine (SM2)
SM2 is located in an isolated power region in order to minimize power consumption in case SM2 is not used.
SM2 runs either with a slow clock (25 kHz nominal) or a fast clock (26 MHz) depending on operation mode.
During start-up or shut-down the slow clock is always used. When SM2 is in active mode, the 26 MHz clock
can be used if it is available. The availabiliy of the 26 MHz clock is given by setting the PMU input signal
available_26mhz_i to logic 1.
SM2 Start-up Sequence
• Start HPBG.
• Measure VBAT and check if VBAT > 3.2 V. If yes proceed, otherwise turn off.
• Start SD1 (VDD_VCORE).
• Start SD2 (VDDP_DIG).
• Un-mask the enable of the following LDOs (in sequence): VRF2, VRF1, VPLL.
• Release RESET1_N that goes to the baseband sub-system.
• Enable the AHB interface.
Figure 42 Power on sequence
Issue 1 NOKIA INTERNAL USE ONLY Page 6 – 9
Copyright © 2013 Nokia. All rights reserved.