DC1205A Datasheet, PDF (7/24 Pages) Linear Integrated Systems – 500mA Wide Input Voltage Range Step-Down LED Driver with 10:1 Dimming

LT3592
PIN FUNCTIONS
R_T (Pin 1): Programs the frequency of the internal oscillator.
Connect a resistor from R_T to ground. Refer to Table 1 or
the Typical Performance Characteristics for resistor values
that result in desired oscillator frequencies.
BRIGHT (Pin 2): Used to program a 10:1 dimming ratio
for the LED current. Drive this pin above 1.4V to command
maximum intensity or below 0.3V to command minimum
intensity. This pin can be PWMed at 150Hz for brightness
control between the 1x and 10x current levels.
SHDN (Pin 3): Used to shutdown the switching regulator
and the internal bias circuits. This pin can be PWMed at
150Hz for brightness control.
V_IN (Pin 4): Supplies current to the LT3592’s internal cir-
cuitry and to the internal power switches. Must be locally
bypassed. For automotive applications, a pi network with a
cap from V_IN to GND, a series inductor connected between
V_IN and the power source, and another cap from the far
end of the inductor to GND is recommended.
DA (Pin 5): Allows the external catch diode current to be
sensed to prevent current runaway, such as when V_IN is
high and the duty cycle is very low. Connect this pin to
the anode of the external catch Schottky diode.
SW (Pin 6): The SW pin is the output of the internal power
switch. Connect this pin to the inductor and the cathode
of the switching diode.
BOOST (Pin 7): Provides a drive voltage, higher than the
input voltage to the internal bipolar NPN power switch.
BOOST will normally be tied to the SW pin through a 0.1μF
capacitor. An internal Schottky is provided for the boost
function and an external diode is not needed. An external
Schottky diode should be connected between BOOST and
CAP for single LED applications or whenever a higher
BOOST voltage is desired.
CAP (Pin 8): Output of the step-down converter and also
an input to the LED current sense amplifier. Connect the
filter capacitor, inductor, and the top of the external LED
current sense resistor to this pin.
OUT (Pin 9): Drives the LED or LEDs and is the other
input to the LED current sense amplifier. Connect this pin
to the anode of the top LED in the string, the bottom of
the external LED current sense resistor, and the top of the
V_FB resistor divider.
V_FB (Pin 10): The feedback node for the output voltage
control loop. Tie this node to a resistor divider between OUT
and GND to set the maximum output voltage of the step-
down converter according to the following formula:
V_OUT
=
1.21•
R1+ R2
R2
where R1 connects between OUT and V_FB and R2 connects
between V_FB and GND.
Exposed Pad (Pin 11): Ground. The underside exposed
pad metal of the package provides both electrical contact
to ground and good thermal contact to the printed circuit
board. The device must be soldered to the circuit board
for proper operation.
3592fc
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