6
LTC1775
Leaving V
PROG
open allows the output voltage to be set by
an external resistive divider between the output and
V
OSENSE
.
PGND (Pin 9): Driver Power Ground. Connects to the
source of the bottom N-channel MOSFET, the (–) terminal
of C
VCC
and the (–) terminal of C
IN
.
BG (Pin 10): Bottom Gate Drive. Drives the gate of the
bottom N-channel MOSFET between ground and INTV
CC
.
INTV
CC
(Pin 11): Internal 5.2V Regulator Output. The
driver and control circuits are powered from this voltage.
Decouple this pin to power ground with a minimum of
4.7µF tantalum or other low ESR capacitor.
BOOST (Pin 12): Topside Floating Driver Supply. The (+)
terminal of the bootstrap capacitor connects here. This pin
swings from a Schottky diode drop below INTV
CC
to V
IN
+
INTV
CC
.
TG (Pin 13): Top Gate Drive. Drives the top N-channel
MOSFET with a voltage swing equal to INTV
CC
superim-
posed on the switch node voltage.
SW (Pin 14): Switch Node. The (–) terminal of the boot-
strap capacitor connects here. This pin swings from a
diode drop below ground up to V
IN
.
TK (Pin 15): Top MOSFET Kelvin Sense. MOSFET V
DS
sensing requires this pin to be routed to the drain of the top
MOSFET separately from V
IN
.
V
IN
(Pin 16): Main Supply Input. Decouple this pin to
ground with an RC filter (1Ω, 0.1µF) for applications
above 3A.
EXTV
CC
(Pin 1): INTV
CC
Switch Input. When the EXTV
CC
voltage is above 4.7V, the switch closes and supplies
INTV
CC
power from EXTV
CC
. Do not exceed 7V at this pin.
SYNC (Pin 2): Synchronization Input for Internal Oscilla-
tor. The oscillator will nominally run at 150kHz when open,
225kHz when tied above 1.2V, and will lock over a 1.5:1
clock frequency range.
RUN/SS (Pin 3): Run Control and Soft Start Input. A
capacitor to ground at this pin sets the ramp time to full
current output (approximately 1s/µF). Forcing this pin
below 1.4V shuts down the device.
FCB (Pin 4): Forced Continuous Input. Tie this pin to
ground to force synchronous operation at low load
currents, to a resistive divider from the secondary output
when using a secondary winding, or to INTV
CC
to enable
Burst Mode operation at low load currents.
I
TH
(Pin 5): Error Amplifier Compensation Point. The
current comparator threshold increases with this control
voltage, forcing inductor current to be roughly propor-
tional to V
ITH
. Nominal voltage range for this pin is 0V to
2.4V.
SGND (Pin 6): Signal Ground. Connect to the (–) terminal
of C
OUT
.
V
OSENSE
(Pin 7): Output Voltage Sense. Feedback input
from the remotely sensed output voltage or from an
external resistive divider across the output.
V
PROG
(Pin 8): Output Voltage Programming. When
V
OSENSE
is connected to the output, V
PROG
< 0.8V selects
a 3.3V output and V
PROG
> 3.5V selects a 5V output.
UU
U
PI FU CTIO S
