Sanyo VPC-CG20 Service Manual page 8

1-3. PWA POWER CIRCUIT DESCRIPTION
1. Outline
This is the main power circuit, and is comprised of the follow-
ing blocks.
Switching controller (IC501)
Digital 3.25 V power output (L5021)
Digital 1.8 V power output (L5031)
CMOS sensor 2.8 V power output (L5061)
LCD backlight system power output (L5071)
Motor system 5.3 V power output (L5301)
2. Switching Controller (IC501)
This is the basic circuit which is necessary for controlling the
power supply for a PWM-type switching regulator, and is pro-
vided with seven built-in channels and linear regulator is pro-
vided with one channel (CH8).
Only CH1 (motor system), CH2 (digital 3.25 V system), CH3
(digital 1.8 V system), CH6 (CMOS sensor), and CH7 (LCD
backlight system) are used.
Feedback from BOOST 5.3 V (CH1), VDD 3 (CH2), VDD 1.8
(CH3), VAA 2.8 (CH6), LCD backlight system (CH7) power
supply outputs are received, and the PWM duty is varied so
that each one is maintained at the correct voltage setting level.
Feedback for the backlight system (CH7) is provided to the
both ends voltage of registance so that regular current can
be controlled to be current that was setting.
2-1. Short-circuit protection circuit
If output is short-circuited for the length of time determined
by the resister setting of IC501, all output is turned off. The
control signal (P ON) are recontrolled to restore output.
3. Digital 3.25 V Power Output
VDD 3 V is output. VDD 3 is so that PWM control can be
carried out at the internal circuit of the switching controller
(IC501).
4. Digital 1.8 V Power Output
VDD 1.8 is output. VDD 1.8 is so that PWM control can be
carried out at the internal circuit of the switching controller
(IC501).
5. LCD Backlight Power Output
Regular current (approximately 20 mA) is being transmitted
to LED for LCD backlight. Detecting for the switching control-
ler (Pin (C3) of IC501) current flowing along connecting
registance so that PWM can be controlled.
6. Motor System 5.3 V Power Output
BOOST 5.3 V is output. BOOST 5.3 V output is so that PWM
control can be carried out at the internal circuit of the switch-
ing controller (IC501).
7. CMOS Sensor 2.8 V Power Output
VAA 2.8 is output.
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