Nikon COOLPIX S550 Repair Manual page 79

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)
Boost 5.0 V output system (L5301)
Digital VDD3 output system (L5002)
Digital VDD1.2 output system (L5003)
Analog -7.5 V (A) output system (L5004, Q5004)
Analog +12 V (A) output system (L5005, Q5001, Q5003)
Backlight output system (L5007, Q5007, Q5008)
Analog +3.5 V (A) output system (IC502)
Digital VDD1.8 output system (IC501 built-in LD0)
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 (ch_1)
PWM drive step-up/step-down circuit ...... 1 (ch_2)
PWM drive step-down circuit ...... 1 (ch_3)
PWM drive inverter circuit ...... 1 (ch_4)
PWM drive step-up circuit ...... 2 (ch_5 and ch_7)
PWM drive step-up/step-down switching circuit ...... 1 (ch_6)
Variable regulator ...... 1 (ch_8 and ch_9)
Only ch_1 (BOOST 5.0 V), ch_2 (VDD3), ch_3 (VDD1.2), ch_4
(-7.5 V (A)), ch_5 (+13 V (A)), ch_6 (not used), ch_7 (back-
light), ch_8 (not used) and ch_9 (VDD1.8) are used.
2-1. Damage Prevention Circuit
When the input detection voltage for the short-circuit protec-
tion circuit block drops to the setting value or below as a re-
sult of an output short-circuit, the capacitor that is connected
to pin (A6) of IC501 starts charging. When the appropriated
capacitor has charged, all output is turned 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 protection circuit. To reset output, remove the
cause of the problem and then resend a control signal.
3. BOOST 5.0 V Output System (L5301)
BOOST 5.0 V (5.0 V) is output. Feedback for the output volt-
age is provided to the switching controller (Pin (B7) of IC501)
so that control can be carried out.
While DSC is operating, power is also supplied to IC502 (+3.5
V (A) output).
While DSC is operating, carry out PWM control. While DSC is
stopping, switch to PFM control, and the output voltage also
drops (3.7 V), provides greater efficiency at times of low loads
(only the 8-bit microprocessor is driven).
4. Digital VDD3 Output System (L5002)
VDD3 (3.25 V) is output. Feedback for the output voltage is
provided to the switching controller (Pin (F3) of IC501) so
that PWM control can be carried out.
While DSC is operating, power is also supplied to IC501 built-
in LD0 (VDD1.8).
5. Digital VDD1.2 Output System (L5003)
VDD1.2 V (1.26 V) is output. Feedback for the output voltage
is provided to the swiching controller (Pin (C3) of IC501) so
that PWM control can be carried out.
6. Analog -7.5 V (A) Output System (L5004, Q5004)
-7.5 V (A) (-7.5 V) is output. Feedback for the output voltage
is provided to the switching power controller (Pin (C5) of IC501)
so that PWM control can be carried out.
7. Analog +12 V (A) Output System
(L5005, Q5001, Q5003)
+13.0 V (A) (13 V) is output. Feedback for the output voltage
is provided to the switching power controller (Pin (D5) of IC501)
so that PWM control can be carried out.
8. Backlight System Output System (L5007, Q5007,
Q5008)
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 (C4) 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.
9. Analog +3.5 V (A) Output System (IC502)
+3.5 V (A) (3.5 V) is output. It is generated by using the sim-
plicial LD0 (IC502) from the BOOST.
10. Digital VDD 1.8 Output System
(IC501 built-in LD0)
VDD 1.8 (1.8 V) is output. It is generated by IC501 built-in
LD0 from VDD3. Feedback for the output voltage is provided
to the switching power controller (Pin (G2) of IC501) so that
the output value can be controlled.
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- E5･ S550 -
INC
VMA21024-R.3750.A