LT3474/LT3474-1
PIN FUNCTIONS
DNC(Pins1,16):Donotconnectexternalcircuitrytothese
pins, or tie them to GND. Leave the DNC pins floating.
SHDN (Pin 10): The SHDN pin is used to shut down the
switching regulator and the internal bias circuits. The
2.6V switching threshold can function as an accurate
under-voltage lockout. Pull below 0.3V to shut down the
LT3474/LT3474-1. Pull above 2.65V to enable the LT3474/
OUT (Pin 2): The OUT pin is the input to the current sense
resistor. Connect this pin to the inductor and the output
capacitor.
LT3474-1. Tie to V if the SHDN function is unused.
IN
LED (Pin 3): The LED pin is the output of the current sense
resistor. Connect the anode of the LED here.
REF (Pin 11): The REF pin is the buffered output of the
internal reference. Either tie the REF pin to the V pin for
ADJ
V (Pin 4): The V pin supplies current to the internal
a 1A output current, or use a resistor divider to generate a
IN
IN
circuitry and to the internal power switch and must be
lower voltage at the V pin. Leave this pin unconnected
ADJ
locally bypassed.
if unused.
SW (Pin 5): The SW pin is the output of the internal power
switch. Connect this pin to the inductor and switching
diode.
V (Pin 12): The V pin is the output of the internal error
C
c
amp. The voltage on this pin controls the peak switch
current. Use this pin to compensate the control loop.
BOOST (Pin 6): The BOOST pin is used to provide a drive
voltage,higherthantheinputvoltage,totheinternalbipolar
NPN power switch.
V
(Pin 13): The V
pin is the input to the internal
ADJ
ADJ
voltage to current amplifier. Connect the V
pin to the
ADJ
REF pin for a 1A output current. For lower output cur-
rents, program the V pin using the following formula:
ADJ
BIAS (Pin 7): The BIAS pin connects through a Schottky
diode to BOOST. Tie to OUT.
I
= 1A • V /1.25V.
LED
ADJ
PWM (Pin 14): The PWM pin controls the connection of
GND (Pins 8, 15, Exposed Pad Pin 17): Ground. Tie both
GND pins and the Exposed Pad directly to the ground
plane.TheExposedPadmetalofthepackageprovidesboth
electrical contact to ground and good thermal contact to
the printed circuit board. It must be soldered to the circuit
board for proper operation.
the V pin to the internal circuitry. When the PWM pin is
C
low, the V pin is disconnected from the internal circuitry
C
and draws minimal current. If the PWM feature is unused,
leave this pin unconnected.
R (Pin 9): The R pin is used to set the internal oscilla-
T
T
tor frequency. Tie an 80.6k resistor from R to GND for a
T
500kHz switching frequency.
3474fd
6
Linear [ Linear ]
