LT3763
11
3763fb
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pin FuncTions
GND (Pin 12, Pin 23, Pin 28, Exposed Pad Pin 29):
Ground. The exposed pad must be soldered to the PCB.
CTRL2 (Pin 13): Thermal Control Input to Reduce the
Regulated Output Current.
CTRL1 (Pin 14): The CTRL1 pin sets the regulated output
current. The maximum control voltage is 1.5V. Above 1.5V,
there is no change in the regulated current.
SS (Pin 15): The Soft-Start Pin. Place an external capacitor
to ground to limit the regulated current during start-up
conditions. The soft-start pin has an 11µA charging cur
-
rent. When the voltage at this pin is lower than voltages at
CTRL1 a
nd CTRL2, it overrides both signals and determines
the regulated current.
SENSE
–
(Pin 16): SENSE
–
is the noninverting input of the
error amplifier for the current regulation loop. The reference
current, based on CTRL1, CTRL2, SS or FBIN determines
the regulated voltage between SENSE
+
and SENSE
–
.
SENSE
+
(Pin 17): SENSE
+
is the inverting input of the
error amplifier for the current regulation loop. This pin
is connected to an external current sense resistor. The
voltage drop between SENSE
+
and SENSE
–
is measured
against the voltage drop across an internal resistor at the
input to the current regulation loop.
V
C
(Pin 18): A resistor and capacitor connected in series
to the V
C
pin provide the necessary compensation for the
stability of the average current loop. Typical values are 5k
to 60k for the resistor and 2.2nF to 10nF for the capacitor.
ISMON (Pin 19): ISMON is the buffered output of the
output current sense amplifier. This voltage output enables
monitoring the averaged output current of the LED driver
with a voltage of 20 • (V
SENSE
+
– V
SENSE
–
). The capacitive
loading to this pin should be less than 1nF.
RT (Pin 20): A resistor from the RT pin to ground sets the
switching frequency between 200kHz and 1MHz. When
using the SYNC function, set the frequency to be at least
20% lower than the SYNC pulse frequency. This pin is
current-limited to 55µA. Do not leave this pin open.
SYNC (Pin 21): Frequency Synchronization Pin. This pin
allows the switching frequency to be synchronized to an
external clock. The RT resistor should be chosen to oper
-
ate the internal clock at 20% slower than the SYNC pulse
frequency
. This pin should be grounded when not in use.
P
WM (Pin 22): The input pin for PWM dimming of LEDs.
When low, all switching is terminated and the PWM_OUT
pin is low. This pin should be connected to INTV
CC
when
not in use.
PWM_OUT (Pin 24): This pin can drive an external FET
for PWM dimming of LEDs. The pull-up and pull-down
impedances of the driver are 2.2Ω and 0.9Ω, respectively.
Do not force any voltage on this pin.
TG (Pin 25): TG is the top FET gate drive pin that controls
the state of the external high side power FET. The driver
pull-up impedance is 2.2Ω, and pull-down impedance is
1.3Ω. Do not force any voltage on this pin.
SW (Pin 26): The SW pin is used internally as the lower
rail for the floating top FET gate driver. Externally, this node
connects the two power FETs and the inductor.
BOOST (Pin 27): The BOOST pin provides a floating 5V
regulated supply for the top FET gate driver. An external
schottky diode is required from the INTV
CC
pin to the
BOOST pin to charge the BOOST capacitor when the SW
pin is near ground.
