LG C2100, Service Manual

Page: 21 / 135

3. TECHNICAL BRIEF
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3.3 26 MHz Clock (VCTCXO, X500)
The 26 MHz clock(X500) consists of a TCXO(Temperature Compensated Crystal Oscillator) which
oscillates at a frequency of 26 MHz. It is used within the Si4205, digital base band chipset (U101,
AD6527)
3.4 Power Supplies for RF Circuits (RF LDO, U503)
Two regulators are used for RF circuits. One is MIC5255 (U503), and the other is one port of AD6537B
(U102).
MIC5255 (U503) supplies power to transceiver (SI4205, U505). One port of AD6537B supplies power
to VCTCXO (X500). Main power (VBAT) from battery is used for PAM (SKY77325, U501) because
PAM requires high power.
RF PARTS
10K
R515
2V75_VVCXO
100p
C528
2
GND
3
OUT
VCC
4
1
VCONT
26MHz
X500
2.2u
C539
C540
0.1u
100
R510
AFC
Figure 3-6 VCTCXO CIRCUIT DIAGRAM
(1608)
(1608)
RF_LDO
VBAT
RF2.85V
C536
C529
4.7u
4.7u
U503
BYP
4 3
EN
2
GND
IN
1
OUT
5
MIC5255-2.85BM5
C535
22n
CLKON
Figure 3-7 RF LDO CIRCUIT DIAGRAM
Supplier Voltage Powers enabled signal
U503(VRF) 2.85 V U505, U501 CLKON
U102(VVCXO) 2.75 V X501
Battery(VBAT) 3.4 ~ 4.2 V U501, U503
Table 3-2 RF POWER SUPPLIERS