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1-3. PWA POWER CIRCUIT DESCRIPTION
1. Outline
This is the main power circuit, and is comprised of the follow-
ing blocks.
Switching power control IC (IC501)
Analog 12 V (A) output system (L5006, Q5001, Q5008, IC506)
Analog -6 V (A) output system (L5007, Q5004, IC506)
Analog 3.3 V (A) output system (IC507)
Digital VDD3 output system (L5003, D5002, D5003)
Digital VDD1.2 output system (L5004, D5003)
Backlight output system (L5005, Q5002, Q5007)
Boost power (L5301, D5301)
2. Switching Power 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 eight built-in channels.
PWM/PFM switching step-up circuit …… 1 (ch1)
PWM drive step-up/step-down circuit …… 1 (ch2)
PWM drive step-up and step-down circuit …… total 4 (ch3
and ch5~ch7)
PWM drive inverter circuit …… 1 (ch4)
Variable regulator …… 1 (ch8)
Only ch1 (starting IC, lens drive, 8-bit microprocessor and
ch3 source), ch2 (digital 3.25 V), ch3 (digital 1.2 V), ch4 (ana-
log -6 V), ch5 (analog 12 V), ch6 (not used), ch7 (backlight)
and ch8 (not used) are used. Feedback from ch1-ch5 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 power (ch7) is provided so that
regular current can be controlled to be current that was set-
ting.
PWM/PFM switching can be carried out for ch1, so that PFM
operation is enabled when the DSC is stopped (when the
power is off) which provides greater efficiency at times of low
loads (only the 8-bit microprocessor is driven).
2-1. Damage Prevention Circuit
When a short-circuit is generated for a constant period of time,
the capacitor that is connected to pin (1) of IC501 turns all
output off. It is also equipped with an overheating protection
circuit, so that when the element temperature becomes higher
than a certain temperature, all output is turned off in the same
way as for a short-circuit. To reset output, remove the cause
of the problem and then resend a control signal.
3. ch1 Output System
3.6 V is output. Feedback for the 3.6 V output is provided to
the switching controller (Pin (36) of IC501) so that PWM con-
trol can be carried out. Also, it is 3.3 V (A) power source. While
DSC is stopped, control switches to PFM control.
4. ch2 Output System
VDD3 is output. Feedback for the VDD3 output is provided to
the switching controller (Pin (45) of IC501) so that PWM con-
trol can be carried out.
5. ch3 Output System
VDD1.2 is output. Feedback for the VDD1.2 output is pro-
vided to the swiching controller (Pin (44) of IC501) so that
PWM control can be carried out.
6. ch4 Output System
-6 V is output. Feedback for the inverter circuit output is pro-
vided to the switching power controller (Pin (38) of IC501) so
that PWM control can be carried out.
This output is high precision by IC506, and get to -6 V.
7. ch5 Output System
12.0 V (A) is output. Feedback for the step-up circuit output is
provided to the switching power controller (Pin (39) of IC501)
so that PWM control can be carried out.
This output is high precision by IC506, and get to 12 V.
8. ch7 Output System
Regular current is being transmitted to LED for backlight. Step-
down in the voltage from the LED are feedback to the switch-
ing power controller (Pin (42) of IC501) so that PWM control
can be carried out.
The control signal (LCD PWM) from the 8-bit system can be
used to adjust the backlight illumination.
