Datasheet LT3597 (Analog Devices) - 8

LT3597
pin FuncTions BOOST1, BOOST2, BOOST3 (Pins 2, 48, 39):
Boost
VOUT1, VOUT2, VOUT3 (Pins 19, 22, 23):
Buck Output. This Capacitor Pin. This pin is used to provide a voltage that is the buck regulator output voltage sense into the IC. is higher than the input voltage when the switch is on to
LED1, LED2, LED3 (Pins 20, 21, 24):
Constant Current supply current to the switch driver. Sink Pin. These are 3 LED driver outputs, each containing
SW1, SW2, SW3 (Pins 4, 46, 41):
Switch Pin. Connect an open collector, constant current sink. All outputs are the inductor, catch diode and boost capacitor to this pin. matched within ±2% and are individually programmed up
DA1, DA2, DA3 (Pins 6, 44, 43):
Catch Diode Anode. to 100mA using an external resistor at the ISET1-3 pin. This pin is used to provide frequency foldback in extreme Outputs are rated to allow a maximum VOUT1-3 of 42V. situations. Connect the cathode of the LED string to LED1-3. Connect the anode of the LED string to VOUT1-3.
FB1, FB2, FB3 (Pins 7, 34, 35):
Feedback Pin. This pin is regulated to the internal bandgap voltage. The maximum
FAULT (Pin 25):
Fault Detection Pin. Open collector pin Buck output voltage can be set by connecting this pin to used to report open LED faults. FAULT must be externally a resistor divider from VOUT1-3. pulled to a positive supply through a resistor.
EN/UVLO (Pin 9):
Enable and Undervoltage Lockout Pin.
NC (Pin 26):
No Connection Pin. Tie to ground. Accurate 1.51V threshold. UVLO threshold can be pro-
SYNC (Pin 27):
External Clock Synchronization Pin. When grammed by using a resistor divider from VIN. If function an external clock drives this pin, the Buck regulators are is not required, pin can be tied to the VIN pin. synchronized to that frequency. Frequency programmed
T
by the RT pin resistor must be at least 20% less than the
SET (Pin 11):
Thermal Regulation Pin. Programs the LT3597 junction temperature at which LED current begins SYNC pin clock frequency. to derate.
PWM1, PWM2, PWM3 (Pins 30, 29, 28):
PWM Dimming
V
Control Pin. When driven to a logic high, the LED1-3 current
REF (Pin 12):
2.0V Reference Output Pin. This pin can sources up to 200µA and can be used to program TSET sink is enabled. If PWM dimming is not desired, connect and CTRLM. the pin to VREF. Channels can be individually disabled by tying PWM1-3 to ground.
CTRLM (Pin 13):
Master Control Pin. LED current derating vs temperature is achievable for all channels if the voltage
CTRL1, CTRL2, CTRL3 (Pins 33, 32, 31):
Analog Dimming on CTRLM has a negative temperature coefficient using an Control Pin. This pin is used to dim the LED current in an external NTC resistor in a voltage divider from VREF. analog fashion. If the pin is tied to a voltage lower than 1.0V, it will linearly reduce the LED current. If feature is
ISET1, ISET2, ISET3 (Pins 14, 15, 16):
LED Current Pro- unused, connect the pin to VREF. gramming Pin. A resistor to ground programs full-scale LED current.
BIAS (Pin 37):
Supply Pin. This pin is the supply for an internal voltage regulator to internal analog and digital
RT (Pin 17):
Switching Frequency Programming Pin. A circuitry. BIAS must be locally bypassed with a 2.2µF resistor to ground programs the switching frequency capacitor. between 200kHz and 1MHz.
VIN (Pins 50, 51):
Input Supply Pin. VIN must be locally
GND (Pin 18, Exposed Pad Pin 53):
Ground Pin. This is bypassed with a 10µF capacitor to ground. Pins 50 and the ground for both the IC and the switching converters. 51 are internally fused. Exposed pad must be soldered to PCB ground. 3597fa 8 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Revision History Typical Application Related Parts