Datasheet

LTC3703
8
3703fc
FuncTional DiagraM
5
1
UVSD OTSD
CHIP
SD
0.9V
3.2V
4µA
RUN/SS
BANDGAP
SYNC
DETECT
OVER
TEMP
V
CC
UVLO
OSC
% DC
LIMIT
DRIVE
LOGIC
+
–
+
–
+
–
+
–
EXT SYNC
FORCED CONTINUOUS
÷
+
+
–
+
–
+
–
+
–
0.8V
MODE/SYNC
3
COMP
4
FB
16
15
14
13
11
10
9
6
12
V
IN
V
CC
(<15V)
INV
PWM
MIN MAX
0.76V
0.84V
±
OVERCURRENT
12µA
50mV
I
MAX
R
MAX
BOOST
TG
SW
DRV
CC
BG
BGRTN
INV
8
GND
GN16
OT SD 0.8V
REFERENCE
INTERNAL
3.2V V
CC
UV SD
2
f
SET
3703 FD
REVERSE
CURRENT
FB
R
SET
5
C
SS
R2
R1
V
CC
C
VCC
D
B
C
B
V
CC
V
IN
M1
M2
C
OUT
V
OUT
L1
INV
±
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
to 100V without the need for a step-down transformer. 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
FB
pin receives the output voltage
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