LT3684
PIN FUNCTIONS
BD (Pin 1):
This pin connects to the anode of the boost
Schottky diode.
BOOST (Pin 2):
This pin is used to provide a drive
voltage, higher than the input voltage, to the internal bipolar
NPN power switch.
SW (Pin 3):
The SW pin is the output of the internal power
switch. Connect this pin to the inductor, catch diode and
boost capacitor.
V
IN
(Pin 4):
The V
IN
pin supplies current to the LT3684’s
internal regulator and to the internal power switch. This
pin must be locally bypassed.
RUN/SS (Pin 5):
The RUN/SS pin is used to put the
LT3684 in shutdown mode. Tie to ground to shut down
the LT3684. Tie to 2.3V or more for normal operation. If
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.
PG (Pin 6):
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
valid when V
IN
is above 3.5V and RUN/SS is high.
BIAS (Pin 7):
The BIAS pin supplies the current to the
LT3684’s internal regulator. Tie this pin to the lowest
available voltage source above 3V (typically V
OUT
). This
architecture increases efficiency especially when the input
voltage is much higher than the output.
FB (Pin 8):
The LT3684 regulates the FB pin to 1.265V.
Connect the feedback resistor divider tap to this pin.
V
C
(Pin 9):
The V
C
pin is the output of the internal error
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.
RT (Pin 10):
Oscillator Resistor Input. Connecting a resistor
to ground from this pin sets the switching frequency.
Exposed Pad (Pin 11):
Ground. The Exposed Pad must
be soldered to PCB.
3684f
7
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