LG -A155 Service Manual page 36

3.7.3 Functional Description
• Power Subsystem
MT6612 contains several LV (low voltage, 2.8V) linear regulators to provide power supply for every power
domain, including RF circuitry and digital core circuitry. Besides, it has built in a BAT linear regulator which
can be directly connected to battery. The BAT linear regulator is the power source for digital IO and those
LV linear regulators. It supports the Li-ion battery. To keep it work properly, the battery voltage should be
within the range from 3.2V to 4.3V.
The built-in LV linear regulators for RF circuitry are cap-less regulators. It provides high PSRR to keep
excellent RF performance. MT6612 has internal enabling signals from the baseband to control different
part of RF circuitry for optimized power control.
The DIG (digital) LV regulator requires an external capacitor. The main power control state machine is in
the digital baseband circuitry. It requires no external enable signal for the DIG LV regulator. When the 1.2V
power is supplied from the regulator on VDD12 pins, there will be an internal POR (Power-On Reset) to
start the system. An external system reset to start the system is optional according to the application
requirement.
The input pin LDO28EN is used by the host controller to turn on and off the BAT regulator. The host can
control this pin to enable the whole MT6612 system. The enable voltage (V
sure that the control signal meets the enable voltage requirement.
Clock generation
There are two clock domains inside MT6612. The one is the System clock, which supports the RF and the
major MODEM functions, while the other is the LPO clock, which keeps track the Bluetooth clock and
could maintain the Bluetooth link in sleep mode.
MT6612 ha two options for the System clock source. The one is foe one-pin crystal input, and the other is
for external clock source. The input pun ECLK_SEL is used to select between these two alternatives. If the
crystal input is chosen, ECLK_SEL should be tied low, Otherwise, it should be tied high.
Chip power management
There are 4 power modes that MT6612 operates in when it is powered on: Normal mode, Active mode,
Idle mode, and Sleep mode. The following are brief introduction to each mode.
• Power off : Power supply is not enabled or LDO28EN is low.
• Normal mode : When MT6612 is powered on, it firstly enters Normal mode. In this mode, an
internal digital PLL is turned on to supply the clock for baseband circuit.
• Active mode : It is defined as the state that RF circuit will be turned on at the same time.
• Idle mode : When the firmware finishes its task and starts to wait for next hardware trigger, it
forces the hardware to enter this mode. In this mode, Part of the logic, like MCU, will enter a low
power mode. RF circuit might still be operation in the mode.
• Sleep mode : The baseband controller can determine to enter sleep mode to turn off most of
the circuit in MT6612. In sleep mode, the system could be awakened after sleep time expired or
by an external wake up signal from the host controller.
Copyright © 2010 LG Electronics. Inc. All right reserved.
Only for training and service purposes
IH
- 7 -
3. TECHNICAL BRIEF
3. TECHNICAL BRIEF
) of pin LDO28EN is 1.4V. Be
LGE Internal Use Only