LT3681
U
U
U
PI FU CTIO S
PG (Pin 1): The PG pin is the open collector output of an
internal comparator. PG remains low until the FB pin is
within 10% of the final regulation voltage. PG output is
BD (Pin 10): This pin connects to the anode of the internal
boost Schottky diode.
BOOST (Pin 11): This pin is used to provide a drive
voltage, higher than the input voltage, to the internal
bipolar NPN power switch. Connect a capacitor between
this pin and SW.
valid when V is above 3.5V and RUN/SS is high.
IN
BIAS (Pin 2): The BIAS pin supplies the current to the
LT3681’s internal regulator. Tie this pin to the lowest
available voltage source above 3V (typically V ). This
OUT
SW (Pin 12): The SW pin is the output of the internal
power switch. Connect this pin to the inductor, DC and
boost capacitor.
architectureincreasesefficiencyespeciallywhentheinput
voltage is much higher than the output.
FB (Pin 3): The LT3681 regulates the FB pin to 1.265V.
Connect the feedback resistor divider tap to this pin.
V (Pin 13): The V pin supplies current to the LT3681’s
IN
IN
internal regulator and to the internal power switch. This
V (Pin 5): The V pin is the output of the internal error
pin must be locally bypassed.
C
C
amplifier. The voltage on this pin controls the peak switch
current. Tie an RC network from this pin to ground to
compensate the control loop.
RUN/SS (Pin 14): The RUN/SS pin is used to put the
LT3681 in shutdown mode. Tie to ground to shut down
the LT3681. Tie to 2.3V or more for normal operation. If
RT(Pin6):OscillatorResistorInput.Connectingaresistor
to ground from this pin sets the switching frequency.
the shutdown feature is not used, tie this pin to the V
IN
pin. RUN/SS also provides a soft-start function; see the
Applications Information section.
DA (Pin 8): This is the anode of the integrated power
Schottky diode. High frequency, large amplitude currents
flow through this pin, so tie it to ground through a low
impedance connection.
GND (Pins 4, 7, Exposed Pad 15): All three of these
terminals internally connect to the LT3681 control IC’s
signal return, while exposed pad 15 performs the added
function of providing a low thermal resistance heat flow
path between the IC and the system heatsink. Tie all of
these terminals to a copper pour on the top layer of the
printed circuit board. Please refer to the Applications
Information section for more details.
DC (Pin 9, Exposed Pad 16): These pins connect to the
cathode of the integrated power Schottky diode. High fre-
quency, large amplitude currents flow through these pins,
so tie them to SW through a low impedance connection.
3681f
7
Linear [ Linear ]
