LTC1735 Linear Technology, LTC1735 Datasheet - Page 7

• Manufacturer Part Number: LTC1735
• Description: High Efficiency Synchronous Step-Down Switching Regulator
• Manufacturer: Linear Technology

C
ground sets the operating frequency.
RUN/SS (Pin 2): Combination of Soft-Start and Run
Control Inputs. A capacitor to ground at this pin sets the
ramp time to full output current. The time is approximately
1.25s/ F. Forcing this pin below 1.5V causes the device to
be shutdown. In shutdown all functions are disabled.
Latchoff overcurrent protection is also invoked via this pin
as described in the Applications Information section.
I
current comparator threshold increases with this control
voltage. Nominal voltage range for this pin is 0V to 2.4V.
FCB (Pin 4): Forced Continuous/Synchronization Input.
Tie this pin to ground for continuous synchronous opera-
tion, to a resistive divider from the secondary output when
using a secondary winding or to INTV
Mode operation at low load currents. Clocking this pin with
a signal above 1.5V
allows cycle-skipping at low load currents and synchro-
nizes the internal oscillator with the external clock.
SGND (Pin 5): Small-Signal Ground. All small-signal
components such as C
the loop compensation resistors and capacitor(s) should
single-point tie to this pin. This pin should, in turn, connect
to PGND.
V
external resistive divider across the output.
SENSE
SENSE
Built-in offsets between SENSE
conjunction with R
PI FU CTIO S
TH
OSC
OSENSE
U
(Pin 3): Error Amplifier Compensation Point. The
(Pin 1): External capacitor C
–
+
(Pin 7): The (–) Input to the Current Comparator.
(Pin 8): The (+) Input to the Current Comparator.
(Pin 6): Receives the feedback voltage from an
U
SENSE
P–P
U
OSC
disables Burst Mode operation but
set the current trip threshold.
, C
SS
, the feedback divider plus
–
and SENSE
OSC
CC
from this pin to
to enable Burst
+
pins in
EXTV
INTV
ever EXTV
in the Applications Information section. Do not exceed 7V
on this pin and ensure EXTV
PGND (Pin 10): Driver Power Ground. Connects to the
source of bottom N-channel MOSFET, the anode of the
Schottky diode, and the (–) terminal of C
BG (Pin 11): High Current Gate Drive for Bottom
N-Channel MOSFET. Voltage swing at this pin is from
ground to INTV
INTV
EXTV
ered from this voltage. Decouple to power ground with a
1 F ceramic capacitor placed directly adjacent to the IC
together with a minimum of 4.7 F tantalum or other low
ESR capacitor.
V
to power ground.
SW (Pin 14): Switch Node Connection to Inductor and
Bootstrap Capacitor. Voltage swing at this pin is from a
Schottky diode (external) voltage drop below ground to
V
BOOST (Pin 15): Supply to Topside Floating Driver. The
bootstrap capacitor is returned to this pin. Voltage swing
at this pin is from a diode drop below INTV
INTV
TG (Pin 16): High Current Gate Drive for Top N-Channel
MOSFET. This is the output of a floating driver with a
voltage swing equal to INTV
switch node voltage SW.
IN
IN
.
(Pin 13): Main Supply Pin. Must be closely decoupled
CC
CC
CC
CC
CC
. This switch closes and supplies V
).
(Pin 12): Output of the Internal 5.2V Regulator and
(Pin 9): Input to the Internal Switch Connected to
Switch. The driver and control circuits are pow-
CC
is higher than 4.7V. See EXTV
CC
.
CC
CC
V
superimposed on the
IN
.
LTC1735
CC
IN
CC
.
power when-
CC
connection
to (V
IN
7
+