Nokia 8208 Service Manual page 135

RM-384
System Module and User Interface
Figure 61 Power On sequence
The mobile terminal can use the power key or a charger to power up.
Power Key
When the power key is pressed, the PMIC enters the power-up sequence. Pressing the power key causes the
KPD_PWR (KPD_PWR pin in 7205 schematic) pin to VPH_PWR. The KPD_PWR signal is not part of the keypad
matrix. The power key is only connected to the PMIC. This means that when the power key is pressed, an
interrupt will be generated to the PMIC and then power on the MCU. The MCU reads the PMIC's interrupt and
notifies that it is a ON_KEY_N interrupt. The MCU reads the status of the ON_KEY_N signal using the control bus. If
the KPD_PWR signal stays high for a certain time, the PMIC accepts this as a valid power-on state and continues
with the software baseband initialization. If the power key does not indicate a valid power-on situation, the
MCU powers off the baseband.
Charger
Charging is controlled by start-up charging circuitry in order to detect and start charging in cases the main
battery is empty and the PMIC has no supply.
External Supply Source is detected
If a valid source is applied to VCHG and the battery voltage of VPH_PWR exceeds PMIC's valid UVLO (2.85V)
threshold, the power-on sequence of PMIC is initiated and enables its internal regulators. UVLO is the minimum
voltage required for PMIC operation. If the entire power-on sequence is successful, the appropriate interrupt
from PMIC will be sent to the MSM. Once the battery voltage rises above 3.0V (min. MSM operation voltage),
code start running on MSM. The MSM reads PMIC registers to identify the power source and whether battery
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