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6.18. Main Board Power Supply Section
6.18.1. 3.3V and 1.2V Power Supply Descriptions
1. IC800, IC801 is Synchronous Step-Down DC/DC Converter with Auto-Skip Eco-mode to increase light load efficiency.
2. Oscillation frequency is set at approximately 700kHz (Frequency is changed at Light Load.).
3. Q803, Q804, R809, R815, C812, R816 are Sequence circuit. (After 1.2V DC-DC converter is turned on, 3.3V(IC801)'s opera-
tion is turned on.)
4. D803, D801 are the Zener Diode for Over voltage protection.
5. Q800, R839, C800, R820 are the switch circuit which turns off a S3.3V power supply at the time of Sleep mode.
LVIN
R800
0(1608)
6.18.2. 5V Power Supply Descriptions
IC802 is low dropout three-terminal regulator.
+3.3V
+3.3V
S3.3V
0(2125)
R802
NC
Q800
L800
4.7u
NC
R839
NC
C800
PWRDWN2
7B;7C;1:1F
+5V
LVIN
+5VD
NC
D805
IC802
3
2
IN
OUT1
4
OUT2
ADJ
1
65
+1.2V
LVIN
R812
L801
2.2u
0(1608)
+5VD
Q803
R816
1k
Q804
(1)
R815
10k
C812
NC
S5V
0(1608)
R827
NC
Q809
R828
NC
C826
NC
S3.3V
Q808
NC
KX-MB2085CXW/KX-MB2090CXW
+1.2V
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Troubleshooting
