FLY E185
Service Manual
CKT Confidential
Page 16 of 47
3.3 Principle of Power Management circuit
3.3.1 Charger and protection logic
Over-temperature Protection: If the die temperature of PMU exceeds 150°C, the PMU will
automatically disable all the LDOs except the V
rtc
. Once the over-temperature state is resolved, a
new power on sequence is required to enable the LDOs.
Battery Charger: The battery charger is optimized for the Li-ion batteries. The typical charging
procedure can be divided into three phases: pre-charging mode, the constant current charging
mode, and the full voltage charging mode. Figure 173shows the flow chart of the charging
procedure. Most of the charger circuits are integrated in the PMU except for one PNP, NMOS and
one accurate resistor for current sensing. These components should be applied externally.
3.3.2 Power-on/off Sequence
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)
Pulling PWRKEY low is the typical way to turn on the handset. The V
core
buck converter will be
turned-on first, and then V
a
/V
io
LDOs turn-on at the same time. After V
a
/V
io
turn-on, V
m
buck and
then V
usb
/V
mc
LDOs, and finally V
rf
/V
tcxo
LDOs will be turn on. The supplies for the baseband are
ready and then the system reset ends at the moment when the V
core
/V
a
/V
io
/V
m
/V
usb
/V
mc
/V
rf
/V
tcxo
are
fully turned-on to ensure the correct timing and function. After that, baseband would 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 baseband.
2. RTC module generate PWRBB to wake up the system
If the RTC module is scheduled to wake up the handset at some time, the PWRBB signal will
directly send to the PMU. In this case, PWRBB becomes high at the specific moment and let PMU
power-on just like the sequence described above. This is the case named RTC alarm.
3. Valid charger plug-in (CHRIN voltage is within the valid range)
Charger plugging-in will also turn on the handset if the charger is valid (no OVP take place).
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 these 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.
Figure: States of mobile handset and regulator
Under-voltage Lockout (UVLO)
The UVLO state in the PMU prevents startup if the initial voltage of the main battery is below the
3.2V threshold. It ensures that the handset is powered-on with the battery in good condition. The
UVLO function is performed by a hysteretic comparator which can ensure the smooth power-on
