LTC3703_15 Datasheet, PDF (8/34 Pages) Linear Technology – 100V Synchronous Switching Regulator Controller

LTC3703
Functional Diagram
R_SET
GN16
2
f_SET
4µA
C_SS
R2 R1
RUN/SS
5
3.2V
–
0.9V ⁺
UVSD OTSD
CHIP
SD
MODE/SYNC
1
COMP
3
0.8V
+
FB
4
+ FB
–
16 ^VIN
EXT SYNC
SYNC
DETECT
OSC
FORCED CONTINUOUS
INV
÷
% DC
LIMIT
–
PWM
+
+MIN–
+MAX–
V_CC
(<15V)
12
OVER
TEMP
BANDGAP
0.76V
0.84V
V_CC
UVLO
OVERCURRENT
12µA
50mV
±
I_MAX
5
R_MAX
±
INV
REVERSE
CURRENT
DRIVE
LOGIC
V_CC
BOOST
15
TG
14
SW
13
DRV_{CC 11}
BG
10
BGRTN
9
INV ₆
D_B
V_IN
C_B
M1
M2
L1
GND ₈
C_OUT
V_OUT
V_CC
C_VCC
OT SD
0.8V
REFERENCE
INTERNAL
3.2V V_CC
UV SD
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