U8655
Maintenance Manual
9 Principles and Failure Analysis
Issue 1.0 (2012-02-23)
Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
25
Subsystem Module
Unit
Function
Power
distribution
network and
power
management
function
Power distribution
network
Includes filter networks and PCB traces for the
power supply.
PM8029
enhanced
function
Battery management,
charging circuit,
charging mode, and
charging protection
Manages battery charging and discharging, provides
overcharging and over-discharging protection, and
charges the capacitor that supplies power to
maintain the real-time clock (RTC).
Board circuit power
management
(power-on/off
analysis)
Mainly controls the low-dropout (LDO) regulator
power supply to flexibly manage power supply.
Based on the service status and the requirements of
the interface power supply specifications and
power-saving analysis, the board software manages
the power supplies to the units on the board to
reduce power consumption.
RTC
The built-in RTC circuit uses a sleep clock of
32.768 kHz to provide precise time.
HKADC
Contains 8 MPP interfaces. Analog-to-digital
conversion can be implemented inside the PM8029.
TCXO driver
The PM8029 has a built-in TCXO driver providing
two analog signal output channels and two digital
signal output channels.
UVLO
Provides the Undervoltage-Lockout (UVLO)
function. When the input voltage is lower than the
threshold for a specific period of time, the phone
powers off.
Over temperature
protection
When the on-chip junction temperature exceeds
150°C, the phone powers off.
Internal driver circuit
Provides one vibration motor driver and one speaker
driver.
Interrupt
management
The built-in interrupt manager handles related
interrupt signals.
USB driver
Supports USB 2.0; does not support USB OTG.
9.2 Baseband Unit
9.2.1 Power-on Management Circuits
On the U8655N, most power supplies are provided by the power management chip PM8029.
