LTC3703
FuncTional DiagraM
R
SET
2
f
GN16
SET
OVERCURRENT
12µA
4µA
I
MAX
–
+
5
R
MAX
50mV
–
+
RUN/SS
–
+
5
INV
CHIP
SD
C
SS
0.9V
3.2V
UVSD OTSD
V
CC
EXT SYNC
+
–
MODE/SYNC
SYNC
DETECT
OSC
1
3
D
B
V
BOOST
TG
REVERSE
CURRENT
IN
FORCED CONTINUOUS
INV
15
14
13
C
B
COMP
M1
SW
–
DRIVE
LOGIC
PWM
+
+
–
0.8V
FB
% DC
LIMIT
+
FB
÷
DRV
CC
11
10
4
V
IN
BG
16
M2
R1
R2
MIN
MAX
–
–
+
+
BGRTN
INV
9
6
V
0.84V
0.76V
CC
(<15V)
L1
12
V
OUT
GND
OVER
TEMP
C
8
BANDGAP
V
CC
UVLO
OUT
OT SD
0.8V
REFERENCE
INTERNAL
3.2V V
UV SD
CC
V
CC
C
VCC
3703 FD
operaTion (Refer to Functional Diagram)
The LTC3703 is a constant frequency, voltage mode con-
troller for DC/DC step-down converters. It is designed to
be used in a synchronous switching architecture with two
external N-channel MOSFETs. Its high operating voltage
capability allows it to directly step down input voltages up
to100Vwithouttheneedforastep-downtransformer. For
circuit operation, please refer to the Functional Diagram
of the IC and Figure 1. The LTC3703 uses voltage mode
control in which the duty ratio is controlled directly by
the error amplifier output and thus requires no current
sense resistor. The V
pin receives the output voltage
FB
feedback and is compared to the internal 0.8V reference
by the error amplifier, which outputs an error signal at the
COMP pin. When the load current increases, it causes a
3703fc
8
Linear Systems [ Linear Systems ]
