Micromax X249, Руководство по обслуживанию

Страница: 12 / 52

X249 L3 Service Manual
3. Flow Chart of Troubleshooting
3-1.Baseband
3-1-1. Phone does not start up troubleshooting
Power-on Sequence and Protection Logic:
The PMU handles the powering ON and OFF of the handset. There are three ways to power-on the handset
system :
①
Push PWRKEY (Pull the PWRKEY pin to the low level)
②
RTC module generate PWRBB to wakeup the system
③
Valid charger plug-in (CHRIN voltage is within the valid range)
Pulling PWRKEY low is the typical way to turn on the handset. The Vcore buck converter will be turned-on first,
and then Va/Vio/Vm LDOs turn-on at
the same time. After that, the supplies for the baseband are ready and it will send the PWRBB signal back to PMU
for acknowledgement. To successfully
power-on the handset, PWRKEY should be kept low until PMU receives the PWRBB from BB. Besides, the
system reset ends at the moment when the
Vcore/Va/Vio/Vmare fully turned-on to ensure the correct timing and function.
If the RTC module is scheduled to wakeup the handset at some time, the PWRBB signal will directly control the
PMU. In this case, PWRBB becomes
high at the specific moment and let PMU power-on just like the on-sequence described above. This is the case
named RTC alarm.
Charger plugging-in will also turn on the handset if the charger is a valid charger. However, if the battery voltage is
too low to power-on the handset
(UVLO state), the system won
’
t be turned-on by any of the three ways. In this case, charger will charge the
battery first and the handset will be
powered-on automatically as long as the battery voltage is high enough.