LT3476 typicAl perForMAnce chArActeristics TA = 25°C, unless otherwise noted.SHDN and PWM Pins Current vsSHDN and PWM Pins ThresholdCAP Pins Overvoltage ThresholdVoltagevs Temperaturevs Temperature 120 1.6 36.0 100 PWM 1-4 1.4 35.5 80 1.2 35.0 60 1.0 TAGE THRESHOLD (V) 34.5 VOL CURRENT (µA) 40 0.8 34.0 SHDN PIN THRESHOLD (V) 20 0.6 33.5 CAP1-4 OVER 0 0.4 33.0 0 4 8 12 16 –45 –20 5 30 55 80 105 130 –45 –20 5 30 55 80 105 130 PIN VOLTAGE (V) TEMPERATURE (°C) TEMPERATURE (°C) 3476 G10 3476 G11 3476 G12 pin FunctionsVC1, VC4, VC3, VC2, (Pins 1, 12, 13, 38): Error Ampli- VADJ4, VADJ3, VADJ2, VADJ1, (Pins 14, 15, 36, 37): LED fier Compensation Pin. When PWM is low, VC pin floats Current Adjustment Pin. Sets voltage across external sense external compensation capacitor to save state for next cycle. resistor between CAPn and LEDn. Connect directly to LED1, LED2, LED3, LED4, (Pins 2, 5, 8, 11): Non- REF for full-scale threshold of 105mV, or use signal vales Inverting Input of Current Sense Error Amplifier. Connect between GND and REF to modulate LED current. VADJ pin directly to LED current sense resistor terminal. Switcher input range is 1.25V maximum. will regulate this node to a voltage of 0.1 • VADJ below the PWM4, PWM3, PWM2, PWM1, (Pins 16, 17, 34, 35): CAP node. Also connected to CAP node through external Signal low turns off the channel—disables the main switch, sense resistor and to anode of LED string. Do not allow reduces quiescent supply current to the channel, and causes this pin to float independently of corresponding CAP input the VC pin for the channel to become high impedance. pin. In applications where the LED current is low and the SHDN (Pin 18): Shutdown Pin. Higher than 1.5V turns PVIN changes widely, connect the output filter capacitor the device on. to LEDn. NC (Pins 19, 20, 21, 30, 31, 32): Not Used. Connect to CAP1, CAP2, CAP3, CAP4, (Pins 3, 4, 9, 10): Inverting GND (Pin 39) for better heat dissipation. input of current sense error amplifier. Connect directly to other terminal of LED current sense resistor. Also con- SW4, SW3, SW2, SW1, (Pins 22, 23, 24, 25, 26, 27, 28, 29): nected to output filter capacitor and cathode of external Switch Pin. Connect to external inductor and anode of external Schottky rectifier. CAP greater than the overvoltage protect Schottky rectifier. Minimize area of SW trace and use a threshold will inhibit switching. GND plane to reduce EMI. Adjacent pins of same name are internally connected. RT (Pin 6): Oscillator Programming Pin. Place resistor connected to GND to program oscillator frequency. VIN (Pin 33): Input Supply Pin. Must be locally bypassed. REF: (Pin 7): Reference Output Pin. Connect to VADJ pin GND (Pin 39): Signal and Power GND. Solder exposed to get full-scale LED current. Connect to resistor dividers pad directly to ground plane. The exposed pad metal of to program VADJ pins to values lower than 1.05V. Bypass the package provides both electrical contact to ground to local GND with 0.1µF capacitor. and good thermal contact to the printed circuit board. It must be soldered to the circuit board for proper operation. 3476fb 5 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
