Voxtel W420, Руководство по ремонту

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circuit, Sim card interface circuit, backlight control circuit, display circuit and camera process circuit etc.
Before introduce these circuit cell, it is necessary to know clock circuit and power management in the
system
——
because these two are the base or working
7.2 System clock circuit introduction:
Clock is the base of system control in every control system. So, it is necessary to know the output and
control theory of clock in W420 mobile phone.
There are 2 kind of clock in the system: one is 32.768KHz for display time
—
—provided by
Y201(32.768KHz crystal); the other is work clock for system working——provided by(26MHz crystal)
1. RTC
——
Real Time Clock
Y201 connect to U200 through the matching network combined with C201, C204, C203, C204 and
R201, provide RTC for U200
Power supply of Y203 is provided by H1 in U202, it is V-RTC in the theory structure
V-RTC can be defined as 1.8V, 1.5V and 1.3V by software (There is 1.5V in W420)
Power supply of RTC circuit provided by main battery VBAT usually, and provided by standby battery
(standby battery provide V-RTC only) when main battery lack of electric power or take off the main battery (e.g.
when changing Sim card) . Electric power provided by standby battery is limited (support RTC circuit for only a
few hours). Therefore, it is necessary to keep power supply provided by VBAT in sure time interval that prevent
RTC information missing.
2. System clock circuit
Y202 (26MHz crystal) provide base value for system clock
C206, R201, D201, C202, R220 and C205 provide matching circuit for Y202. One side of this circuit
connect to pin C12 of U202, which provide AFC (AFC
：
Automatic Frequency Control) for 26MHz crystal; the
other side of this circuit pass through a more complicated path to provide system working clock:
a: first, input 48pin on U602, provide working clock for U602
b: then, processed in U602, pass through 47pin on U602 input Y9 on U200
——
provide 26MHz working
clock for DBB
c: and then, processed in U201, pass through N1 output 13MHz clock for other exterior equipments:
pass through E1 on U202 provide ABB clock
7.3: System power management introduction:
In the mobile phone system, because of using many equipment and interface, lead to considering many
kinds of power is necessary (generally 6 or 7). As the technology improved, now, most of these electrical
source are provided by flat chip. Using power management provide additional power only when the flat chip
can not match design conditions
According to the classify principle above, introduce power management of W420 follows:
a: Source from flat
Source from flat is provided by U202(ABB), its power and use are in the table:
Title Pin voltage Current Benefited Chip
V_DBB
J1
、
H2
1.5V 170mA
U201
：
main working voltage
V_ABB H10 2.8V 80mA U202
：
analog circuit working voltage
V_IO
B1
、
B2
2.8V 100mA
U104
、
U200
、
U301
、
U302
和
U305
：
system digital
IO interface working voltage
V_FLASH G1 2.8V 60mA U300
：
Flash working voltage
V_SRAM F1 2.8V 50mA U300
：
RAM working voltage
V_SIM B4 2.9V 10mA
U201
：
Sim interface working voltage
V_RTC D1 1.5/1.3V U203
：
RTC circuit working voltage
Table 7.1: A19 system flat power distribute
b: Source outside the flat
W420 use U309,U301,U303
——
LDO(Low Dropout) provide system additional power needing 2.8V,
1.8V and 1.578V, for prevent lack of power in system