lt3755-2 Linear Technology Corporation, lt3755-2 Datasheet
lt3755-2
Related parts for lt3755-2
lt3755-2 Summary of contents
Page 1
... IN DescripTion The LT 3755, LT3755-1 and LT3755-2 are DC/DC control- ® lers designed to operate as a constant-current source for driving high current LEDs. They drive a low side external N-channel power MOSFET from an internal regulated 7.15V supply. The fixed frequency, current mode architecture results in stable operation over a wide range of supply and output voltages ...
Page 2
... LT3755/LT3755-1/LT3755-2 absoluTe MaxiMuM raTings V ............................................................................40V IN SHDN/UVLO (Note 3) ................................................40V ISP , ISN .....................................................................75V INTV ...................................................... V CC GATE, PWMOUT (Note 4) ......................... INTV CTRL, PWM, OPENLED .............................................12V SS, FB ..........................................................3V C REF SYNC ..........................................................................8V pin conFiguraTion TOP VIEW REF PWM 2 17 GND SYNC OR OPENLED 3 SS ...
Page 3
... ISN = 0V ) ISN PWM = 5V (Active), ISP = ISN = 48V PWM = 0V (Standby), ISP = ISN = 48V V = 100mV (ISP – ISN) 1V < VC < 2V PWM = 0V ISP = ISN ISP = ISN FB Current Out of Pin OPENLED Falling (LT3755 and LT3755-2) PWMOUT Falling R = 100k 10k T MIN TYP MAX UNITS 4 ...
Page 4
... INTVCC IN SHDN/UVLO = 0V, INTV = 7V CC E-, I-Grades H-Grade I Drops Below 1µA VIN SHDN/UVLO = 1.15V SHDN/UVLO = 1.30V I = 0.5mA (LT3755 and LT3755-2) OPENLED LT3755-1 Only LT3755-1 Only LT3755-1 Only C = 3300pF 3300pF L Note 3: For V below 6V, the SHDN/UVLO pin must not exceed V IN proper operation. ...
Page 5
... TEMPERATURE (°C) 37551 G04 Switching Frequency 10000 1000 100 (k) T 37551 G07 LT3755/LT3755-1/LT3755-2 V Threshold vs V (ISP – ISN) ISP 103 CTRL 102 101 100 ISP VOLTAGE (V) V Voltage vs Temperature REF 2 ...
Page 6
... LT3755/LT3755-1/LT3755-2 Typical perForMance characTerisTics Quiescent Current 2.0 PWM = 0V 1.5 1.0 0 (V) IN 37551 G10 INTV Voltage (V) IN 37551 G13 SENSE Current Limit Threshold vs Duty Cycle 115 110 105 100 DUTY CYCLE (%) ...
Page 7
... FB threshold (by an external power supply spike, for example), the OPENLED pull-down will be de-asserted and the PWMOUT pin will be driven low to protect the LEDs from an overcurrent event. Do not leave the FB pin open. If not used, connect to GND. LT3755/LT3755-1/LT3755-2 ISP –0.5 ISN –1.0 – ...
Page 8
... VC pin from all internal loads. PWMOUT pin follows PWM pin. PWM has an internal pull-down resistor. If not used, connect to INTV OPENLED (Pin 9/Pin 3, LT3755 and LT3755-2): An open- collector pull-down on OPENLED asserts if the FB input is greater than the FB regulation threshold minus 50mV (typical) ...
Page 9
... TO 1MHz OSCILLATOR FAULT 10µA + LOGIC 1.25V + – T FREQ LIM 165°C PROG SS PWM V IN LDO – 1.25V A8 INTV 7.15V + CC GATE R Q DRIVER S I SENSE SENSE + A4 – GND RAMP OPENLED – 1.2V OPTION FOR FB + LT3755 AND LT3755-2 OPTION FOR RT SYNC LT3755-1 37551 BD 37551fd ...
Page 10
... First, when the FB pin exceeds a voltage 50mV lower (–4%) than the FB regulation voltage, the pull-down driver on the OPENLED pin is activated (LT3755 and LT3755-2 only). This func- tion provides a status indicator that the load may be disconnected and the constant-voltage feedback loop is taking control of the switching regulator ...
Page 11
... The falling UVLO value can be accurately set by the resistor divider. A small 2.1µA pull-down current is active when SHDN/UVLO is below the threshold. The purpose of this current is to allow the user to program the rising hysteresis. LT3755/LT3755-1/LT3755-2 The following equations should be used to determine the values of the resistors: V ...
Page 12
... LT3755/LT3755-1/LT3755-2 applicaTions inForMaTion When V is higher than 1.2V, the LED current is CTRL regulated to: 100mV I = LED R LED The LED current programming feature can increase total dimming range by a factor of 10. The CTRL pin should not be left open (tie not used). The CTRL pin ...
Page 13
... LT3755/LT3755-1/LT3755-2 Duty Cycle Considerations Switching duty cycle is a key variable defining converter operation, therefore, its limits must be considered when programming the switching frequency for a particular application. The fixed minimum on-time and minimum off-time (see Figure 4) and the switching frequency define the minimum and maximum duty cycle of the switch, respectively ...
Page 14
... LED event to have occurred. The key difference between the LT3755 and A(MAX) LT3755-2 is the behavior of the OPENLED pin when the FB pin crosses and re-crosses the FB overvoltage threshold (1.31V typ). The LT3755-2 asserts/de-asserts OPENLED freely when crossing the 1.31V threshold. The LT3755, by comparison, de-asserts OPENLED when FB exceeds 1 ...
Page 15
... To achieve the same LED ripple current, the required filter capacitor is larger in the boost and buck-boost mode ap- plications than that in the buck mode applications. Lower LT3755/LT3755-1/LT3755-2 operating frequencies will require proportionately higher capacitor values. Soft-Start Capacitor Selection For many applications important to minimize the inrush current at start-up. The built-in soft-start circuit ...
Page 16
... LT3755/LT3755-1/LT3755-2 applicaTions inForMaTion Schottky Rectifier Selection The power Schottky diode conducts current during the interval when the switch is turned off. Select a diode rated for the maximum SW voltage. If using the PWM feature for dimming important to consider diode leakage, which increases with the temperature, from the output during the PWM low interval ...
Page 17
... L1: WÜRTH ELEKTRONIK 744870220 M1: VISHAY SILICONIX SI7454DP D1: DIODES INC. - PDS5100 M2: VISHAY SILICONIX SI2318DS LT3755/LT3755-1/LT3755-2 node to eliminate interplane coupling to sensitive signals. The lengths of the high dI/dt traces: 1) from the switch node through the switch and sense resistor to GND, and 2) from the switch node through the Schottky rectifier and filter capacitor to GND should be minimized ...
Page 18
... LT3755/LT3755-1/LT3755-2 applicaTions inForMaTion GND COMPONENT DESIGNATIONS REFER TO “50W WHITE LED HEADLAMP DRIVER” SCHEMATIC Figure 5. Boost Converter Suggested Layout VIAS TO GROUND PLANE ...
Page 19
... 0.0 0.4 0.6 0.2 LOAD (A) LT3755/LT3755-1/LT3755-2 50W White LED Headlamp Driver L1 22µ SHDN/UVLO ISP REF 187k 16.9k LT3755-2 CTRL ISN 100k INTV CC NTC GATE RT1 100k SENSE OPENLED PWM SS RT PWMOUT C SS 0.01µF V GND INTV 28.7k R ...
Page 20
... LED PWM LED 1A/DIV I L1 1A/DIV 2µs/DIV 0 Buck Mode 1.4A LED Driver 1M V ISP IN SHDN/UVLO 107k V ISN REF FB CTRL LT3755-2 PWMOUT PWM OPENLED SS RT GATE V GND INTV SENSE C CC 28.7k 375kHz 47k C2 4.7µF 0.001µF 37551 TA03b C3 110k 200k 4.7µF ...
Page 21
... D1: DIODES, INC SBM540 Minimum PWM Pulse Switching Waveform GATE INDUCTOR CURRENT 1A/DIV PWM I LED 500mA/DIV 500ns/DIV LT3755/LT3755-1/LT3755-2 V ISP IN SHDN/UVLO V ISN REF CTRL 0.22µF PWMOUT LT3755-2 PWM INTV CC 2200pF GATE OPENLED SENSE SS V GND 22k 13k 800kHz 470pF 37551 TA06b 0.2 500mA 16V M2 4.7µ ...
Page 22
... INPUT VOLTAGE ( 15µH D1 50V M1 2.2µF 2 392k 0.02 Q1 GATE SENSE SHDN/UVLO 20.0k V REF LT3755-2 PWMOUT CTRL PWM INTV CC ISP 100k ISN OPENLED SS V GND RT C 28.7k 0.01µF 4.7k 375kHz 4700pF Buck-Boost Mode LED Current vs Low Input Voltage 37551 TA07b 0.1 M2 100V 21.5V 2.2µ ...
Page 23
... MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX LT3755/LT3755-1/LT3755-2 MSE Package MSE Package 16-Lead Plastic MSOP, Exposed Die Pad ...
Page 24
... LT3755/LT3755-1/LT3755-2 package DescripTion 3.50 ± 0.05 1.45 ± 0.05 (4 SIDES) 2.10 ± 0.05 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 3.00 ± 0.10 PIN 1 TOP MARK (NOTE 6) NOTE: 1. DRAWING CONFORMS TO JEDEC PACKAGE OUTLINE MO-220 VARIATION (WEED-2) 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH ...
Page 25
... Revised Entire Data Sheet to Include H-Grade Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. LT3755/LT3755-1/LT3755-2 PAGE NUMBER 1-26 37551fd ...
Page 26
... TO 4.7µF 36V 2 LTC4440-5 INTV V BOOST CC CC GND TG TS INP SHDN/UVLO V GATE REF 330k 383k SENSE CTRL INTV LT3755-2 CC 47k FB 100k ISP OPENLED PWM SS ISN RT PWMOUT 0.01µF V GND INTV C CC 28.7k INTV 375kHz 10k 1% 0.01µF 4.7µF M1, M2: VISHAY SILICONIX SI7850DP D1, D2: DIODES, INC SBM540 ...