LTC3728LX Linear Technology, LTC3728LX Datasheet - Page 9

• Manufacturer Part Number: LTC3728LX
• Description: 2-Phase Synchronous Regulators
• Manufacturer: Linear Technology

FU CTIO AL DIAGRA
OPERATIO
Main Control Loop
The IC uses a constant frequency, current mode step-
down architecture with the two controller channels oper-
ating 180 degrees out of phase. During normal operation,
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
INTV
F
IN
+
IN
R
C
5V
U
LP
LP
CC
PLLFLTR
PGOOD
3.3V
EXTV
INTV
PLLIN
SGND (UH PACKAGE PAD)
FCB
V
IN
OUT
50k
CC
0.18 A
CC
3V
U
OSCILLATOR
4.8V
PHASE DET
+
–
0.8V
4.5V
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
1.2 A
6V
4(V
0.86V
FB
SLOPE
COMP
)
I1
S
R
+
–
0.55V
Q
Q
–
DROP
OUT
DET
Figure 2
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
LTC3728L/LTC3728LX
TOP
BOT
INTV
CC
INTV
30k
30k
CC
V
SENSE
SENSE
RUN/SS
BOOST
PGND
OSENSE
SW
I
TG
BG
TH
+
–
1
INTV
TH
resets the RS latch is con-
CC
pin, which is the output of
R1
D
C
C
C
OSENSE
B
R2
C2
SS
B
www.DataSheet4U.com
C
C
V
IN
R
C
OSENSE
R
D
pin receives the
SENSE
1
+
TH
C
relative to
IN
voltage to
+
3728lxfa
9