LT3760
8
3760fc
pin FuncTions
CTRL (Pin 1): CTRL pin voltage below 1V controls
LED current. CTRL voltage can be set by a resistor
divider from V
IN
, V
REF
or an external voltage source.
LED current derating versus temperature is achievable
if the voltage programmed at the CTRL pin has a negative
temperature coefficient using an external resistor divider
from V
REF
pin to GND with temperature dependent
resistance.
T
SET
(Pin 2): Programs LT3760 junction temperature
breakpoint past which LED current will begin to derate.
Program using a resistor divider from V
REF
to GND.
V
REF
(Pin 3): 1.485V Reference Output Pin. This pin can
supply up to 150µA. Can be used to program CTRL, T
SET
and OVP
SET
pin voltages using resistor dividers to GND.
I
SET
(Pin 4): Resistor to GND Programs LED pin current.
See Table 6 in the Applications Information Section.
NC (Pin 5): No Connect. Okay to leave open or to connect
to GND.
LED
x
(Pins 6 to 9, 20 to 23): 8 LED Driver Outputs. Each
output contains an open collector constant current sink. LED
currents are programmable from 20mA to 100mA using a
single resistor at the I
SET
pin. Connect the cathode of each
LED string to an LED pin. Connect the anode of each
LED
string to V
OUT
. Channels can be paralleled for greater LED
current or individually disabled (connect LED to V
OUT
).
PGND (Pins 10, 19, Exposed Pad Pin 29): Power grounds
for the IC and the converter. The package has an exposed
pad (Pin 29) underneath the IC which is the best path for
heat out of the package. Pin 29 should be soldered to
a continuous copper ground plane under the device to
reduce die temperature and increase the power capability
of the LT3760.
SENSE (Pin 11): The Current Sense Input for the Control
Loop. Connect this pin to the sense resistor in the source
of the external power MOSFET.
GATE (Pin 12): Drives the gate of an N-channel MOSFET
from 0V to INTV
CC
.
INTV
CC
(Pin 13): A 7V LDO supply generated from V
IN
and
used to power the GATE driver and some control circuitry.
Must be bypassed with a 4.7µF capacitor to PGND.
V
IN
(Pin 14): Input Supply Pin. Must be locally bypassed
with a 1µF capacitor to PGND.
SHDN/UVLO (Pin 15): The SHDN/UVLO pin has an accurate
1.476V threshold and can be used to program an under volt-
age lockout (UVLO) threshold for system input supply using
a
resistor divider from supply to GND. A 2.4µA pin cur-
rent hysteresis allows programming of UVLO hysteresis.
SHDN/UVLO above 1.476V turns the part on and removes
a 2.4µA sink current from the pin. SHDN/UVLO < 0.7V
reduces V
IN
current < 20µA. If the shutdown function is
not required, it should be forced above 1.476V or con-
nected directly to V
IN
.
FAULT (Pin 16): Active low if any or all LED strings have
an open fault. If fault(s) removed, FAULT flag returns high.
Fault status is only updated during PWM high state and
latched during PWM low.
SYNC (Pin 17): Allows synchronization of boost converter
switching frequency to an external clock. RT resistor should
be programmed for f
OSC
20% below SYNC frequency. If
unused, connect to GND.
V
OUT
(Pin 18): Boosted Output Voltage of the Converter.
Connect a capacitor from this pin to PGND. Connect the
anode of each LED (string) to V
OUT
.
GND (Pin 24): Signal Ground.
RT (Pin 25): A resistor to GND programs switching fre-
quency f
OSC
between 0.1MHz and 1MHz.
V
C
(Pin 26): Output of Both Transconductance Error
Amplifiers for the Converter Regulation Loop. The most
commonly used gm error amplifier (LED) regulates V
OUT
to ensure no LED pin falls below 1V. The other gm error
amplifier
(OVP) is activated if all LEDs fail open and a
regulated maximum V
OUT
is required. Connect a resistor
and capacitor in series from the V
C
pin to GND.
PWM (Pin 27): Input Pin for PWM Dimming Control. Above
1.4V allows converter switching and below 0.7V disables
switching. The PWM signal can be driven from 0V to 6V.
If unused, connect to V
REF.
OVP
SET
(Pin 28): Programs maximum allowed V
OUT
regu-
lation level if all LEDs are open circuit. Program using a
resistor divider from V
REF
to GND.
