1
2.2 PMU
U802 is the system’s power manager unit，abbreviation PMU. It‘s responsible for system’s
battery’s charge and discharge, boot and shutdown, providing all the power needed by
system.
2.2.1 The timing of system’s boot
1.
When the power key was pressed down, or the test point TP1412 was short to ground,
U802’s pin of K11 which was called by name PHONE_ON_N was became low level.
2.
PMU initialize, and turn the pinN11 to low，and turn on the switch of system’s power
MOSFET—U803.
3.
PMU puts out all the voltage according to the boot timing.
4.
PMU pulls the pin PON_RESET_N to high level，and reset the U101.
5.
After the CPU U101 reset, it pulls the PS_HOLD signal to high, in order to keep boot
status.
Note: If the power key was pressed up before the PS_HOLD was pulled to high, the phone
will not boot normally.
2.2.2 The voltages put out from PMU
If the system can’t boot normally, we often should to check the voltages put out from the
PMU. The correct voltage can refer to the table listed in the figure 12 and figure 13.
