LTC3728 Linear Technology, LTC3728 Datasheet - Page 9

• Manufacturer Part Number: LTC3728
• Description: 2-Phase Synchronous Step-Down Switching Regulator
• Manufacturer: Linear Technology

FU CTIO AL DIAGRA
OPERATIO
Main Control Loop
The LTC3728 uses a constant frequency, current mode
step-down architecture with the two controller channels
operating 180 degrees out of phase. During normal opera-
tion, each top MOSFET is turned on when the clock for that
channel sets the RS latch, and turned off when the main
current comparator, I
R6
R5
V
F
IN
V
+
IN
R
C
5V
U
SEC
LP
LP
PLLFLTR
PGOOD
3.3V
EXTV
INTV
PLLIN
SGND
FCB
V
IN
OUT
50k
CC
0.18µA
CC
1.5V
U
OSCILLATOR
4.7V
PHASE DET
+
–
4.5V
0.8V
U
+
–
(Refer to Functional Diagram)
+
–
–
+
1
, resets the RS latch. The peak
CLK1
CLK2
INTERNAL
–
+
–
+
–
+
–
+
SUPPLY
V
LDO
REG
5V
REF
0.86V
0.74V
0.86V
0.74V
BINH
FCB
V
V
OSENSE1
OSENSE2
W
DUPLICATE FOR SECOND
CONTROLLER CHANNEL
1.2µA
6V
4(V
0.86V
FB
SLOPE
COMP
)
I1
S
R
+
–
0.55V
Q
Q
–
DROP
Figure 2
OUT
DET
45k
–
+
+
4(V
SHDN
+
RST
FB
B
3mV
inductor current at which I
trolled by the voltage on the I
each error amplifier EA. The V
voltage feedback signal, which is compared to the internal
reference voltage by the EA. When the load current in-
creases, it causes a slight decrease in V
the 0.8V reference, which in turn causes the I
)
BOT
TOP ON
–
SHDN
FCB
START
45k
SOFT
RUN
–
+
OV
2.4V
EA
I2
SWITCH
–
+
+
–
LOGIC
V
FB
0.80V
0.86V
TOP
BOT
INTV
CC
INTV
30k
30k
CC
V
RUN/SS
SENSE
SENSE
BOOST
PGND
OSENSE
SW
BG
I
TG
TH
+
–
1
INTV
TH
resets the RS latch is con-
CC
pin, which is the output of
R1
OSENSE
D
C
C
C
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B
D
R2
C2
SS
B
C
SEC
C
V
IN
R
C
LTC3728
OSENSE
R
pin receives the
D
SENSE
1
+
TH
+
C
C
relative to
voltage to
IN
SEC
+
3728fb
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