LTC3703
FuncTional DiagraM
R
SET
2
GN16
f
SET
OVERCURRENT
12µA
–
+
50mV
–
+
5
C
SS
3.2V
RUN/SS
0.9V
–
+
UVSD OTSD
EXT SYNC
OSC
FORCED CONTINUOUS
3
COMP
–
PWM
+
DRIVE
LOGIC
INV
+
–
REVERSE
CURRENT
BOOST
TG
SW
DRV
CC
BG
+
MIN
–
MAX
+ –
BGRTN
INV
0.76V
0.84V
15
14
13
11
10
9
6
L1
OVER
TEMP
GND
V
OUT
8
C
OUT
M2
C
B
V
CC
D
B
V
IN
M1
CHIP
SD
5
I
MAX
R
MAX
4µA
±
±
INV
1
MODE/SYNC
SYNC
DETECT
4
R2
R1
16
0.8V
FB
V
IN
+
+ FB
–
÷
% DC
LIMIT
12
V
CC
(<15V)
BANDGAP
V
CC
UVLO
OT SD
0.8V
REFERENCE
INTERNAL
3.2V V
CC
UV SD
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
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
3703fc
8
LINEAR [ LINEAR INTEGRATED SYSTEMS ]
