LTC1735IS Linear Technology, LTC1735IS Datasheet - Page 9

• Manufacturer Part Number: LTC1735IS
• Description: IC REG SW STEP-DOWN SYNC 16-SOIC
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC1735IS

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.8 ~ 6 V
• Current - Output: 3A
• Frequency - Switching: 300kHz
• Voltage - Input: 4 ~ 30 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

FU CTIO AL DIAGRA
OPERATIO
Main Control Loop
The LTC1735 uses a constant frequency, current mode
step-down architecture. During normal operation, the top
MOSFET is turned on each cycle when the oscillator sets
the RS latch and turned off when the main current
comparator I
current at which I
voltage on Pin 3 (I
amplifier EA. Pin 6 (V
tions, allows EA to receive an output feedback voltage V
from an external resistive divider. When the load current
increases, it causes a slight decrease in V
0.8V reference, which in turn causes the I
R1
LTC1735F
V
PGOOD
U
ONLY
OSENSE
R2
6V
RUN/SS
1.2 A
V
C
0.74V
0.86V
FB
SS
0.8V
1
U
+
–
+
–
+
–
resets the RS latch. The peak inductor
EA
LATCHOFF
CURRENT
1
OV
gm =1.3m
U
START
OVER-
SOFT-
C
resets the RS latch is controlled by the
RUN
SD
C
+
C
OSC
C
TH
OSENSE
OSC
(Refer to Functional Diagram)
), which is the output of error
R
C
SGND
), described in the pin func-
OSC
4(V
I
0.86V
TH
SLOPE COMP
FB
)
SYNC
W
ICMP
BURST
DISABLE
FC
A
C
0.17 A
I
1
FB
2.4V
–
+
–
+
BUFFERED
I
TH
S
R
FORCE BOT
relative to the
–
TH
1.2V
SENSE
2k
Q
voltage to
+
+
DROP
OUT
DET
TOP ON
+
45k
30k
3mV
FCB
0.55V
FB
0.8V
–
BOT
45k
30k
SENSE
–
+
+
–
–
+
I
increase until the average inductor current matches the
new load current. While the top MOSFET is off, the bottom
MOSFET is turned on until either the inductor current
starts to reverse, as indicated by current comparator I
the beginning of the next cycle.
The top MOSFET driver is powered from a floating boot-
strap capacitor C
from INTV
MOSFET is turned off. As V
converter will attempt to turn on the top MOSFET continu-
ously (“dropout’’). A dropout counter detects this condi-
tion and forces the top MOSFET to turn off for about 500ns
every tenth cycle to recharge the bootstrap capacitor.
2
F
B
IREV
–
SD
INTV
FC
4.7V
SWITCH
CC
LOGIC
0.8V
REF
+
–
V
CC
IN
V
UVL
TOP
BOT
IN
5.2V
through an external diode when the top
LDO
REG
EXTV
B
. This capacitor is normally recharged
CC
BOOST
SW
TG
INTV
IN
CC
decreases towards V
C
C
D
D
INTV
INTVCC
PGND
B
B
1
BG
CC
+
V
IN
R
LTC1735
SENSE
+
C
IN
V
SEC
OUT
+
+
1735 FD
2
, the
1735fc
9
C
C
, or
V
SEC
OUT
OUT