LT3597
8
3597fa
pin FuncTions
BOOST1, BOOST2, BOOST3 (Pins 2, 48, 39): Boost
Capacitor Pin. This pin is used to provide a voltage that
is higher than the input voltage when the switch is on to
supply current to the switch driver.
SW1, SW2, SW3 (Pins 4, 46, 41): Switch Pin. Connect
the inductor, catch diode and boost capacitor to this pin.
DA1, DA2, DA3 (Pins 6, 44, 43): Catch Diode Anode.
This pin is used to provide frequency foldback in extreme
situations.
FB1, FB2, FB3 (Pins 7, 34, 35): Feedback Pin. This pin is
regulated to the internal bandgap voltage. The maximum
Buck output voltage can be set by connecting this pin to
a resistor divider from VOUT1-3.
EN/UVLO (Pin 9): Enable and Undervoltage Lockout Pin.
Accurate 1.51V threshold. UVLO threshold can be pro-
grammed by using a resistor divider from V
IN
. If function
is not required, pin can be tied to the VIN pin.
T
SET
(Pin 11): Thermal Regulation Pin. Programs the
LT3597 junction temperature at which LED current begins
to derate.
V
REF
(Pin 12): 2.0V Reference Output Pin. This pin can
sources up to 200µA and can be used to program TSET
and CTRLM.
CTRLM (Pin 13): Master Control Pin. LED current derating
vs temperature is achievable for all channels if the voltage
on CTRLM has a negative temperature coefficient using an
external NTC resistor in a voltage divider from VREF.
I
SET1
, I
SET2
, I
SET3
(Pins 14, 15, 16): LED Current Pro-
gramming Pin. A resistor to ground programs full-scale
LED current.
RT (Pin 17): Switching Frequency Programming Pin. A
resistor to ground programs the switching frequency
between 200kHz and 1MHz.
GND (Pin 18, Exposed Pad Pin 53): Ground Pin. This is
the ground for both the IC and the switching converters.
Exposed pad must be soldered to PCB ground.
V
OUT1
, V
OUT2
, V
OUT3
(Pins 19, 22, 23): Buck Output. This
is the buck regulator output voltage sense into the IC.
LED1, LED2, LED3 (Pins 20, 21, 24): Constant Current
Sink Pin. These are 3 LED driver outputs, each containing
an open collector, constant current sink. All outputs are
matched within ±2% and are individually programmed up
to 100mA using an external resistor at the ISET1-3 pin.
Outputs are rated to allow a maximum VOUT1-3 of 42V.
Connect the cathode of the LED string to LED1-3. Connect
the anode of the LED string to VOUT1-3.
FAULT (Pin 25): Fault Detection Pin. Open collector pin
used to report open LED faults. FAULT must be externally
pulled to a positive supply through a resistor.
NC (Pin 26): No Connection Pin. Tie to ground.
SYNC (Pin 27): External Clock Synchronization Pin. When
an external clock drives this pin, the Buck regulators are
synchronized to that frequency. Frequency programmed
by the RT pin resistor must be at least 20% less than the
SYNC pin clock frequency.
PWM1, PWM2, PWM3 (Pins 30, 29, 28): PWM Dimming
Control Pin. When driven to a logic high, the LED1-3 current
sink is enabled. If PWM dimming is not desired, connect
the pin to VREF. Channels can be individually disabled by
tying PWM1-3 to ground.
CTRL1, CTRL2, CTRL3 (Pins 33, 32, 31): Analog Dimming
Control Pin. This pin is used to dim the LED current in an
analog fashion. If the pin is tied to a voltage lower than
1.0V, it will linearly reduce the LED current. If feature is
unused, connect the pin to VREF.
BIAS (Pin 37): Supply Pin. This pin is the supply for an
internal voltage regulator to internal analog and digital
circuitry. BIAS must be locally bypassed with a 2.2µF
capacitor.
V
IN
(Pins 50, 51): Input Supply Pin. V
IN
must be locally
bypassed with a 10µF capacitor to ground. Pins 50 and
51 are internally fused.
