Sony Vaio PCGA-CRWD1, Руководство по обслуживанию

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IC
Confidential
PCGA-CRWD1 (AM)
LTC1735CGN#TR (LINEAR TECHNOLOGY)
HIGH EFFICIENCY SYNCHRONOUS STEP-DOWN
SWITCHING REGULATOR
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1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
C
OSC
RUN/SS
I
TH
FCB
SGND
V
OSENSE
SENSE
–
SENSE
+
TG
BOOST
SW
V
IN
INTV
CC
BG
PGND
EXTV
CC
C
OSC
(Pin 1): External capacitor C
OSC
from this pin to
ground sets the operating frequency.
RUN/SS (Pin 2): Combination of Soft-Start and Run
Control Inputs. A capacitor to ground at this pin sets the
ramp time to full output current. The time is approximately
1.25s/
µ
F. Forcing this pin below 1.5V causes the device to
be shutdown. In shutdown all functions are disabled.
Latchoff overcurrent protection is also invoked via this pin
as described in the Applications Information section.
I
TH
(Pin 3): Error Amplifier Compensation Point. The
current comparator threshold increases with this control
voltage. Nominal voltage range for this pin is 0V to 2.4V.
FCB (Pin 4): Forced Continuous/Synchronization Input.
Tie this pin to ground for continuous synchronous opera-
tion, to a resistive divider from the secondary output when
using a secondary winding or to INTV
CC
to enable Burst
Mode operation at low load currents. Clocking this pin with
a signal above 1.5V
P–P
disables Burst Mode operation but
allows cycle-skipping at low load currents and synchro-
nizes the internal oscillator with the external clock.
SGND (Pin 5): Small-Signal Ground. All small-signal
components such as C
OSC
, C
SS
, the feedback divider plus
the loop compensation resistors and capacitor(s) should
single-point tie to this pin. This pin should, in turn, connect
to PGND.
V
OSENSE
(Pin 6): Receives the feedback voltage from an
external resistive divider across the output.
SENSE
–
(Pin 7): The (–) Input to the Current Comparator.
SENSE
+
(Pin 8): The (+) Input to the Current Comparator.
Built-in offsets between SENSE
–
and SENSE
+
pins in
conjunction with R
SENSE
set the current trip threshold.
EXTV
CC
(Pin 9): Input to the Internal Switch Connected to
INTV
CC
. This switch closes and supplies V
CC
power when-
ever EXTV
CC
is higher than 4.7V. See EXTV
CC
connection
in the Applications Information section. Do not exceed 7V
on this pin and ensure EXTV
CC
≤
V
IN
.
PGND (Pin 10): Driver Power Ground. Connects to the
source of bottom N-channel MOSFET, the anode of the
Schottky diode, and the (–) terminal of C
IN
.
BG (Pin 11): High Current Gate Drive for Bottom
N-Channel MOSFET. Voltage swing at this pin is from
ground to INTV
CC
.
INTV
CC
(Pin 12): Output of the Internal 5.2V Regulator and
EXTV
CC
Switch. The driver and control circuits are pow-
ered from this voltage. Decouple to power ground with a
1
µ
F ceramic capacitor placed directly adjacent to the IC
together with a minimum of 4.7
µ
F tantalum or other low
ESR capacitor.
V
IN
(Pin 13): Main Supply Pin. Must be closely decoupled
to power ground.
SW (Pin 14): Switch Node Connection to Inductor and
Bootstrap Capacitor. Voltage swing at this pin is from a
Schottky diode (external) voltage drop below ground to
V
IN
.
BOOST (Pin 15): Supply to Topside Floating Driver. The
bootstrap capacitor is returned to this pin. Voltage swing
at this pin is from a diode drop below INTV
CC
to (V
IN
+
INTV
CC
).
TG (Pin 16): High Current Gate Drive for Top N-Channel
MOSFET. This is the output of a floating driver with a
voltage swing equal to INTV
CC
superimposed on the
switch node voltage SW.
PIN FUNCTIONS
FUNCTIONAL DIAGRAM
SW
–
+
+
–
0.86V
–
+ 0.55V
2.4V
0.8V
0.86V
I
1
+
–
I
2
+
–
EA
A
BURST
DISABLE
FC
OV
gm =1.3m
Ω
B
–
+ 4.7V
IREV
+
–
+
–
F
FC
S
R
Q
DROP
OUT
DET
0.8V
REF
SWITCH
LOGIC
SD
6V
R1
RUN/SS
C
SS
R
C
V
OSENSE
V
FB
1.2
∝
A
RUN
SOFT-
START
+
OVER-
CURRENT
LATCHOFF
SD
I
TH
C
C
0.17
∝
A
OSC
4(V
FB
)
BUFFERED
I
TH
SLOPE COMP
+ – – +
3mV
ICMP
R2
2k
45k
BOT
TOP ON
FORCE BOT
45k
30k 30k
SENSE
+
SENSE
–
SYNC
1.2V 0.8V
C
TOP
UVL
BOT
INTV
CC
5.2V
LDO
REG
V
IN
+
C
INTVCC
V
OUT
V
SEC
INTV
CC
BG
PGND
V
IN
V
IN
BOOST
TG
INTV
CC
C
B
D
B
D
1
C
OSC
+
C
IN
+
C
SEC
+
C
OUT
EXTV
CC
FCB SGND C
OSC
R
SENSE
1 5 4
13
15
16
14
12
11
10 9 7 8 3 2
6
MD8408B (FUJIFILM MICRODEVICES)
IEEE 1394 PHYSICAL LAYER IC
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