LTC1625
PIN FUNCTIONS
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, 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.
I
TH
(Pin 5):
Error Amplifier Compensation Point. The
current comparator threshold increases with this control
voltage. 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.
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 capacitance.
BOOST (Pin 12):
Topside Floating Driver Supply. The (+)
terminal of the bootstrap capacitor connects here. This pin
swings from a 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
minus a
diode drop, superimposed 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 (4.7Ω, 0.1µF) for applications
above 3A.
6
U
U
U
LINER [ LINEAR TECHNOLOGY ]
