LT3763 60V High Current Step-Down LED Driver Controller Description Features n n n n n n n n n n n n Accurately Control Input and Output Current 3000:1 True Color PWM™ Dimming ±1.5% Voltage Regulation Accuracy ±6% Current Regulation Accuracy 6V to 60V Input Voltage Range Wide Output Range Up to 55V <2µA Shutdown Current Control Pin for Thermal Control of Load Current Input and Output Current Monitor and Limit Open, Short, and C/10 Fault Detection PWM Driver Output for LED Applications Thermally Enhanced 28-Lead FE Package The LT®3763 is a fixed frequency, synchronous, step-down DC/DC controller designed to accurately regulate output currents up to 20A. The average current mode controller will maintain inductor current regulation over a wide output voltage range from 0V to 55V. Output current is set by analog voltages on the CTRL pins and an external sense resistor. Voltage regulation and overvoltage protection are set with a voltage divider from the output to the FB pin. The switching frequency is programmable from 200kHz to 1MHz through an external resistor on the RT pin or with the SYNC pin and an external clock signal. Input and output current sensing provides input current limiting and an accurate measurement of these currents. The FBIN pin is provided for applications requiring a peak power tracking function. Applications n n n n High Power Architectural Lighting Automotive Lighting Aviation and Marine Strobe Lights Solar-Powered Chargers, Laser Diodes Additional features include an accurate external reference voltage for use with the CTRL pins, an accurate UVLO/ EN pin that allows for programmable UVLO hysteresis, a PWM driver for LED applications, output voltage fault detection, and thermal shutdown. L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and True Color PWM is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents including 7199560, 7321203 and others pending. Typical Application 20A, Pulse Width Modulated, Single LED Driver 2.5mΩ VIN 10V TO 30V 84.5k 1k 1µF 100µF 1k 4.7µF 15.4k IVINP IVINN PWM Dimming VIN EN/UVLO TG 220nF VREF 2.2µF 45.3k LT3763 CTRL2 BOOST 1.5µH SW VOUT 6V, 20A MAXIMUM 220µF ×2 INTVCC 470k 47.5kΩ 50k 2.5mΩ 22µF BG CTRL1 10Ω IL 5A/DIV 10Ω GND 50Ω 1nF 50Ω 1nF FBIN SENSE+ IVINMON SENSE– 82.5k 5µs/DIV 33nF 3763 TA01b PWMOUT ISMON PWM SYNC RT PWM 10V/DIV VSW 50V/DIV FAULT 47.5k FB SS 10nF VC 12.1k 59k 3763 TA01 4.7nF 3763f 1 LT3763 Absolute Maximum Ratings Pin Configuration (Note 1) VIN, EN/UVLO, IVINP, and IVINN................................60V SENSE+ and SENSE–..................................................60V CTRL1, CTRL2, FB, and FBIN.......................................3V SYNC and PWM...........................................................6V INTVCC and FAULT.......................................................6V VC, RT, and SS.............................................................3V VREF, IVINMON, and ISMON.........................................3V SW.............................................................................60V BOOST.......................................................................66V BOOST-SW...................................................................6V Operating Junction Temperature (Notes 2, 3) LT3763E/LT3763I............................... –40°C to 125°C LT3763H............................................. –40°C to 150°C Storage Temperature Range................... –65°C to 150°C Lead Temperature (Soldering, 10 sec).................... 300°C TOP VIEW BG 1 28 GND INTVCC 2 27 BOOST VIN 3 26 SW EN/UVLO 4 25 TG VREF 5 24 PWM_OUT IVINN 6 23 GND IVINP 7 IVINMON 8 FAULT 9 29 GND 22 PWM 21 SYNC 20 RT 19 ISMON FBIN 10 18 VC FB 11 GND 12 17 SENSE+ CTRL2 13 16 SENSE– CTRL1 14 15 SS FE PACKAGE 28-LEAD PLASTIC TSSOP θJA = 30°C/W EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB Order Information LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT3763EFE#PBF LT3763EFE#TRPBF LT3763FE 28-Lead Plastic TSSOP –40°C to 125°C LT3763IFE#PBF LT3763IFE#TRPBF LT3763FE 28-Lead Plastic TSSOP –40°C to 125°C LT3763HFE#PBF LT3763HFE#TRPBF LT3763FE 28-Lead Plastic TSSOP –40°C to 150°C Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ Electrical Characteristics The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, VEN/UVLO = 5V unless otherwise noted. PARAMETER CONDITIONS MIN Supply Undervoltage Lockout From Low to High 3.75 VIN Pin Quiescent Current Non-Switching Operation Shutdown Mode VEN/UVLO = 1.4V, Not Switching VEN/UVLO = 0V Input Voltage Range 1.47 EN/UVLO Hysteresis SYNC Pin Threshold (Falling Edge) SYNC Pin Hysteresis MAX 60 V 4.0 4.25 V 1.7 0.2 3.5 2 mA µA 1.52 1.57 6 EN/UVLO Pin Threshold (Falling Edge) EN/UVLO Pin Current TYP EN/UVLO = 1.4V, VIN = 6V 1.4 UNITS V 185 mV 5 µA 1.5 675 1.6 V mV 3763f 2 LT3763 Electrical Characteristics The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, VEN/UVLO = 5V unless otherwise noted. PARAMETER CONDITIONS PWM Pin Threshold (Falling Edge) MIN TYP MAX 1.4 1.5 1.6 PWM Pin Hysteresis 675 UNITS V mV CTRL1 Pin Current VCTRL1 = 1.5V 20 nA CTRL2 Pin Current VCTRL1 = 1.5V, VCTRL2 = 1.5V, VFBIN = 2V 100 nA Reference Reference Voltage (VREF pin) l 1.94 l 48 2 2.06 51 54 V Inductor Current Sensing Full Range SENSE+ to SENSE– VCTRL1 = 2V, VCTRL2 > 2V, VSS = VFBIN = 2V, VC = 1.2V SENSE+ Pin Current VSENSE+ = VSENSE– = 4V SENSE– Pin Current VSENSE +=V SENSE – = 4V, V CTRL1 = 1.5V mV –20 µA –40 µA Internal VCC Regulator (INTVCC Pin) Regulation Voltage ILOAD = 10mA Current Limit VINTVCC = 0V l 4.8 5 5.2 V 60 mA 42 ns 44 ns 50 ns NMOS FET Driver Non-Overlap Time TG to BG Non-Overlap Time BG to TG Minimum On-Time BG (Note 4) Minimum On-Time TG (Note 4) 55 ns Minimum Off-Time BG (Note 4) 140 ns High Side Driver Switch On-Resistance Gate Pull-Up Gate Pull-Down VCBOOST – VSW = 5V 2.2 1.3 Ω Ω Low Side Driver Switch On-Resistance Gate Pull-Up Gate Pull-Down VINTVCC = 5V 2.2 1 Ω Ω Switching Frequency RT = 40.2kΩ RT = 200kΩ l 930 180 1000 200 1070 220 kHz kHz Soft-Start Charging Current 11 µA 750 nA Voltage Regulation Amplifier Input Bias Current VFB = 1.3V 850 gm Feedback Regulation Voltage VSENSE+ = VSENSE– = VCTRL1 = 2V µA/V l 1.188 1.206 1.224 l 1.137 1.16 1.183 V FAULT Comparator Upper FAULT Threshold (FB Rising) Upper FAULT Threshold Hysteresis 40 Lower FAULT Threshold (FB Falling) l Lower FAULT Threshold Hysteresis FAULT Pull-Down Current VFAULT = 2V, VFB = 0V 0.24 0.25 V mV 0.26 V 40 mV 8 mA Input Voltage Regulation FBIN Pin Current VFBIN = 1.5V 150 nA Sense Voltage (VSENSE+ – VSENSE–) VFBIN = 1.22V, VSENSE– = 4V VFBIN = 1.26V, VSENSE– = 4V 10 45 mV mV 3763f 3 LT3763 Electrical Characteristics The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, VEN/UVLO = 5V unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS VISMON Regulated to 1V, VSENSE– = 10V VISMON Regulated to 200mV, VSENSE– = 10V 45 5 50 10 55 15 mV mV VIVINMON Regulated to 1V, VIVIN+ = 12V VIVINMON Regulated to 200mV, VIVIN+ = 12V 46 6 50 10 54 14 mV mV 45 50 55 mV Output Current Monitor Sense Voltage (VSENSE+ – VSENSE–) Input Current Monitor Sense Voltage (VIVIN+ – VIVIN–) Input Current Limit Sense Voltage (VIVIN+ – VIVIN–) l PWM Driver PWM_OUT Driver On-Resistance Gate Pull-Up Gate Pull-Down VINTVCC = 5V PWM to PWM_OUT Propagation Delay Rising Falling VINTVCC = 5V 2.2 0.9 Ω Ω 11 38 ns ns Current Control Loop gm Amp Offset Voltage VSENSE– = 4V, VCTRL1 = 0V, VCTRL2 = 2V Input Common Mode Range VCM(LOW) VCM(HIGH) (Note 5) VCM(HIGH) Measured from VIN to VCM, VSENSE+ = VSENSE– l –3 0 3 0 1.4 Output Impedance V V 3.5 gm l Differential Gain 375 475 1.7 mV MΩ 625 µA/V V/mV Overvoltage FB Overvoltage Protection (VFB Maximum) 1.515 V Overcurrent Overcurrent Protection (VSENSE+ – VSENSE– Maximum) VSENSE– = 0V, RT = 200kΩ, VVC = 1.2V Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LT3763E is guaranteed to meet performance specifications from 0°C to 125°C junction temperature. Specifications over the –40°C to 125°C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. The LT3763I is guaranteed to meet performance specifications over the –40°C to 125°C operating junction temperature range. The LT3763H is guaranteed over the –40°C to 150°C operating junction temperature range. High junction temperatures degrade operating lifetimes; operating lifetime is derated for junction temperatures greater than 125°C. 85 mV Note 3: This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. The maximum rated junction temperature will be exceeded when this protection is active. Continuous operation above the specified absolute maximum operating junction temperature may impair device reliability or permanently damage the device. Note 4: The minimum on- and off-times are guaranteed by design and are not tested. Note 5: The minimum common mode voltage is guaranteed by design and is not tested. 3763f 4 LT3763 Typical Performance Characteristics EN/UVLO Threshold (Falling) EN/UVLO Current 1.52 1.46 5.5 5.0 4.5 4.0 60 42 24 6 42 VIN (V) 3763 G01 60 100 10 1 0.1 6VIN 12VIN 60VIN VREF (V) 2.01 2.0 2.00 42 VIN (V) 1.3 1.2 1.1 TA = 150°C TA = 25°C TA = –50°C 1.0 1.99 –50 –25 60 0 3763 G04 25 50 75 100 125 150 TEMPERATURE (°C) 0.9 6 24 RT Current Limit 42 60 VIN (V) 3763 G05 3763 G06 INTVCC Current Limit SS Current 16 70 6 5 64 52 4 VINTVCC (V) SS CURRENT (µA) 14 58 12 3 2 10 46 40 –50 –25 VREF Current Limit 1.4 2.5 24 25 50 75 100 125 150 TEMPERATURE (°C) 3763 G03 1.5 2.02 TA = 150°C TA = 25°C TA = –50°C 0 3763 G02 VREF Voltage 2.03 6 0.001 –50 –25 VREF CURRENT LIMIT (mA) 24 6 Quiescent Current (Non-Switching) 1.5 6VIN 12VIN 60VIN 0.01 3.0 QUIESCENT CURRENT (mA) QUIESCENT CURRENT (nA) EN/UVLO CURRENT (µA) EN/UVLO THRESHOLD (V) 1.58 VIN (V) RT CURRENT LIMIT (µA) 10000 1000 1.64 1.40 Quiescent Current (Shutdown) 6.0 1.70 1 0 25 50 75 100 125 150 TEMPERATURE (°C) 3763 G07 8 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) 3763 G08 0 0 10 20 30 40 IINTVCC (mA) 50 60 3763 G09 3763f 5 LT3763 Typical Performance Characteristics 6.0 VIN UVLO 4.2 VBOOST – VSW UVLO Thresholds 4.5 4.1 4.0 4.0 3.9 0 3.0 3.7 –50 –25 25 50 75 100 125 150 TEMPERATURE (°C) 0 INTVCC Load Regulation Overvoltage Threshold 4.95 13 TIMEOUT (µs) VFB (V) 1.51 1.49 10 20 30 40 IINTVCC (mA) 50 1.45 –50 –25 60 0 100 OUTPUT CURRENT (%) 80 40 20 Regulated Current vs VFB 150 75 50 25 25 50 75 100 125 150 TEMPERATURE (°C) 3763 G16 25 50 75 100 125 150 TEMPERATURE (°C) 3763 G15 Maximum Output Voltage 125 60 0 3763 G14 Overcurrent Threshold 0 10 –50 –25 25 50 75 100 125 150 TEMPERATURE (°C) 3763 G13 100 0 –50 –25 12 11 1.47 OUTPUT CURRENT (%) VINTVCC (V) Overvoltage Timeout 14 1.53 5.05 0 25 50 75 100 125 150 TEMPERATURE (°C) 3763 G12 1.55 5.00 0 3763 G11 5.10 VSENSE+ – VSENSE– (mV) 2.5 –50 –25 25 50 75 100 125 150 TEMPERATURE (°C) 3763 G10 4.90 3.5 FALLING 3.8 3.0 –50 –25 6VIN 12VIN 60VIN 4.0 RISING VINTVCC (V) VIN (V) VBOOST – VSW (V) 5.0 INTVCC UVLO 0 0 0.5 1.0 1.5 VIN – VOUT (V) 2.0 2.5 3763 G17 100 50 0 –50 1.16 1.17 1.18 1.19 VFB (V) 1.20 1.21 3763 G18 3763f 6 LT3763 Typical Performance Characteristics TG Driver RDS(ON) 4 3 BG Driver RDS(ON) 3 RDS(ON) (Ω) PULL-UP RDS(ON) (Ω) Nonoverlap Time 80 2 PULL-DOWN 1 0 –50 –25 0 PULL-UP 2 1 PULL-DOWN 0 –50 –25 25 50 75 100 125 150 TEMPERATURE (°C) NONOVERLAP TIME (ns) 4 0 BG TO TG 40 TG TO BG 20 0 –50 –25 25 50 75 100 125 150 TEMPERATURE (°C) 3763 G19 60 0 3763 G20 3763 G21 Minimum On-Time Minimum Off-Time 200 25 50 75 100 125 150 TEMPERATURE (°C) Oscillator Frequency 80 1.2 120 HG 80 40 HG 60 0.9 FREQUENCY (MHz) LG MINIMUM ON-TIME (ns) MINIMUM OFF-TIME (ns) 1MHz 160 LG 40 20 0.6 500kHz 0.3 200kHz 0 –50 –25 0 0 –50 –25 25 50 75 100 125 150 TEMPERATURE (°C) 0 3763 G22 1.0 Current Regulation Accuracy 1.0 VCTRL1 = 1.5V VIN = 12V 50 0.5 20 VCTRL1 = 0.75V VIN = 12V 0.5 ACCURACY (%) ACCURACY (%) 30 25 50 75 100 125 150 TEMPERATURE (°C) 3763 G24 Current Regulation Accuracy Regulated Sense Voltage 40 0 3763 G23 60 VSENSE+ – VSENSE– (mV) 0 –50 –25 25 50 75 100 125 150 TEMPERATURE (°C) 0 –0.5 0 –0.5 10 0 0 0.5 1.0 VCTRL1 (V) 1.5 2.0 3763 G25 –1.0 0 2 4 6 VOUT (V) 8 10 3763 G26 –1.0 0 2 4 6 VOUT (V) 8 10 3763 G27 3763f 7 LT3763 Typical Performance Characteristics PWM Driver Delay PWM Driver RDS(ON) 4 40 FALLING DELAY (ns) PULL-UP 2 1 0 –50 –25 0 30 20 RISING 10 PULL-DOWN 0 –50 –25 25 50 75 100 125 150 TEMPERATURE (°C) VSENSE+ – VSENSE– (mV) 3 RDS(ON) (Ω) C/10 Threshold 20 50 0 FAULT Threshold 0 25 50 75 100 125 150 TEMPERATURE (°C) 3763 G30 FAULT Hysteresis Output Current Sense 75 2.0 1.5 UPPER 0.8 0.4 50 VISMON (V) HYSTERESIS (mV) 1.2 VFB (V) FALLING 5 3763 G29 1.6 0 0.5 0 –50 –25 25 50 75 100 125 150 TEMPERATURE (°C) 0 0 25 50 75 100 125 150 TEMPERATURE (°C) Input Current Sense Input Current Limit 8 53 0.5 51 49 100 3763 G34 45 –50 –25 3763 G33 VIN = 12V VOUT = 5V ILIMIT = 20A 4 2 47 25 50 75 VIVINP – VIVINN (mV) 100 6 VOUT (V) VIVINP – VIVINN (mV) 1.0 25 50 75 VSENSE+ – VSENSE– (mV) Output Voltage Load Regulation 55 2.0 1.5 0 3763 G32 3763 G31 0 1.0 25 LOWER 0 –50 –25 VIVINMON (V) RISING 10 0 –50 –25 25 50 75 100 125 150 TEMPERATURE (°C) 3763 G28 0 15 0 25 50 75 100 125 150 TEMPERATURE (°C) 3763 G35 0 0 6 12 ILOAD (A) 18 24 3763 G36 3763f 8 LT3763 Typical Performance Characteristics Output Voltage Load Regulation Efficiency vs Load Current VIN = 48V VOUT = 24V ILIMIT = 10A EFFICIENCY (%) VOUT (V) 24 16 8 0 Efficiency vs Load Current 100 100 95 95 EFFICIENCY (%) 32 90 85 0 3 6 ILOAD (A) 12 9 80 90 85 VIN = 12V VOUT = 5V 0 6 12 18 ILOAD (A) 3763 G37 80 24 VIN = 48V VOUT = 24V 0 3 3763 G38 Shutdown and Recovery 6 ILOAD (A) 9 12 3763 G39 15A Load Step VOUT 5V/DIV SS 2V/DIV VOUT 20mV/DIV AC-COUPLED EN/UVLO 5V/DIV IL 10A/DIV IL 5A/DIV 1ms/DIV 3763 G40 500µs/DIV Solar Powered SLA Battery Charging PWM Dimming IL 500mA/DIV VSW 50V/DIV PWM 10V/DIV 10µs/DIV 3763 G41 3763 G42 FAULT 10V/DIV VIN 500mV/DIV AC-COUPLED IL 2A/DIV VOUT 50mV/DIV AC-COUPLED 50s/DIV 3763 G43 3763f 9 LT3763 Pin Functions BG (Pin 1): BG is the bottom FET gate drive signal that controls the state of the external low side power FET. The driver pull-up impedance is 2.2Ω, and pull-down impedance is 1Ω. Do not force any voltage on this pin. INTVCC (Pin 2): The INTVCC pin provides a regulated 5V output for charging the BOOST capacitor. INTVCC also provides the power for the digital and switching subcircuits. Do not force any voltage on this pin. Bypass with at least a 22µF capacitor to ground. INTVCC is current-limited to 50mA. Shutdown operation disables the output voltage drive. VIN (Pin 3): Input Supply Pin. Must be locally bypassed with at least a 4.7µF low ESR capacitor to ground as close as possible to the exposed pad of the package. EN/UVLO (Pin 4): Enable Pin. The EN/UVLO pin acts as an enable pin and turns on the internal current bias core and sub-regulators at 1.705V and turns off at 1.52V. The pin does not have any pull-up or pull-down, requiring a voltage bias for normal operation. Full shutdown occurs at approximately 0.5V. If unused, the Enable pin may be tied to VIN. VREF (Pin 5): Buffered 2V Reference Capable of 0.5mA Drive. Bypass with at least 1µF capacitor to ground. IVINP (Pin 7): IVINP is the noninverting input of the input current sense amplifier. This pin connects to the input supply VIN and the input current sense resistor. IVINMON (Pin 8): IVINMON is the buffered output of the input current sense amplifier. This pin enables monitoring of the averaged supply current with an output voltage of 20 • (VIVINP – VIVINN). The capacitive loading to this pin should be less than 1nF. FAULT (Pin 9): Output Voltage Fault Detection Pin for Shorted or Open LEDs. Internal comparators pull down this pin when the FB pin voltage is lower than 0.25V or higher than 1.16V and when the inductor current is less than ten percent of the maximum value. This pin should be pulled up to INTVCC with a resistance higher than 10k. FBIN (Pin 10): The FBIN pin enables peak power tracking for solar powered chargers and other similar applications by controlling the output current of the system based on the input voltage. This pin should be tied to VREF if this feature is not used. FB (Pin 11): The feedback pin is used for voltage regulation and overvoltage protection. The feedback voltage is regulated to 1.206V. When the feedback voltage exceeds 1.515V, the overvoltage lockout prevents switching. IVINN (Pin 6): IVINN is the inverting input of the input current sense amplifier. This pin connects to the drain of the high side N-channel power FET and the input current sense resistor. 3763f 10 LT3763 Pin Functions GND (Pin 12, Pin 23, Pin 28, Exposed Pad Pin 29): Ground. The exposed pad must be soldered to the PCB. CTRL2 (Pin 13): Thermal Control Input to Reduce the Regulated Output Current. CTRL1 (Pin 14): The CTRL1 pin sets the regulated output current. The maximum control voltage is 1.5V. Above 1.5V, there is no change in the regulated current. SS (Pin 15): The Soft-Start Pin. Place an external capacitor to ground to limit the regulated current during start-up conditions. The soft-start pin has an 11µA charging current. When the voltage at this pin is lower than voltages at CTRL1 and CTRL2, it overrides both signals and determines the regulated current. SENSE– (Pin 16): SENSE– is the noninverting input of the error amplifier for the current regulation loop. The reference current, based on CTRL1, CTRL2, SS or FBIN determines the regulated voltage between SENSE+ and SENSE–. SENSE+ (Pin 17): SENSE+ is the inverting input of the error amplifier for the current regulation loop. This pin is connected to an external current sense resistor. The voltage drop between SENSE+ and SENSE– is measured against the voltage drop across an internal resistor at the input to the current regulation loop. VC (Pin 18): A resistor and capacitor connected in series to the VC pin provide the necessary compensation for the stability of the average current loop. Typical values are 5k to 60k for the resistor and 2.2nF to 10nF for the capacitor. ISMON (Pin 19): ISMON is the buffered output of the output current sense amplifier. This voltage output enables monitoring the averaged output current of the LED driver with a voltage of 20 • (VSENSE+ – VSENSE–). The capacitive loading to this pin should be less than 1nF. RT (Pin 20): A resistor from the RT pin to ground sets the switching frequency between 200kHz and 1MHz. When using the SYNC function, set the frequency to be at least 20% lower than the SYNC pulse frequency. This pin is current-limited to 55µA. Do not leave this pin open. SYNC (Pin 21): Frequency Synchronization Pin. This pin allows the switching frequency to be synchronized to an external clock. The RT resistor should be chosen to operate the internal clock at 20% slower than the SYNC pulse frequency. This pin should be grounded when not in use. PWM (Pin 22): The input pin for PWM dimming of LEDs. When low, all switching is terminated and the PWM_OUT pin is low. This pin should be connected to INTVCC when not in use. PWM_OUT (Pin 24): This pin can drive an external FET for PWM dimming of LEDs. The pull-up and pull-down impedances of the driver are 2.2Ω and 0.9Ω, respectively. Do not force any voltage on this pin. TG (Pin 25): TG is the top FET gate drive pin that controls the state of the external high side power FET. The driver pull-up impedance is 2.2Ω, and pull-down impedance is 1.3Ω. Do not force any voltage on this pin. SW (Pin 26): The SW pin is used internally as the lower rail for the floating top FET gate driver. Externally, this node connects the two power FETs and the inductor. BOOST (Pin 27): The BOOST pin provides a floating 5V regulated supply for the top FET gate driver. An external schottky diode is required from the INTVCC pin to the BOOST pin to charge the BOOST capacitor when the SW pin is near ground. 3763f 11 LT3763 Block Diagram RSENSE_IN 2.5mΩ VIN RFILTA 1k CFILT 1µF 7 CIN2 47µF RFILTB 1k CIN1 4.7µF CVCC 22µF 6 IVINP 3 IVINN 2 VIN R INPUT CURRENT MONITORING gm = 400µA/V LOW SIDE DRIVER OSCILLATOR 14 IVINMON CTRL1 1.5V BG SYNC – 8 TG SW + – 2V REFERENCE SYNCHRONOUS CONTROLLER Q CBOOST 200nF BOOST + VREF INTERNAL REGULATOR AND UVLO S HIGH SIDE DRIVER CURRENT MIRROR VC PWM_OUT PWM + C/10 COMPARATOR ISMON + – – VOLTAGE REGULATOR AMP gm = 850µA/V 0.25V CTRL2 24 RC 47.5k CC 4.7nF L1 1µH 19 17 16 RFB1 47.5k RS 2.5mΩ VOUT COUT 200µF ×2 11 RFB2 12.1k 1.16V – INTVCC FAULT DETECTION COMPARATORS – RT 82.5k 22 1.206V + 1.206V FB – + + 10 18 50k 11µA SS FBIN 20 OUTPUT MONITORING SENSE– 13 21 0.1V SENSE+ 3k CSS 10nF 1 + gm = 475µA/V RO = 3.5M VCM(HIGH) = VIN – 1.4V – – + 1.5V – – gm AMP + 90k 15 26 1.5V RT + +CONTROL BUFFER – 25 – CREF 2.2µF 5 EN/UVLO + 4 27 INTVCC FAULT RFAULT 47.5k 9 GND (12, 23, 28, 29) 3763 BD Figure 1. Block Diagram 3763f 12 LT3763 Operation The LT3763 utilizes fixed frequency, average current mode control to accurately regulate the inductor current independently from the output voltage. This is an ideal solution for applications requiring a regulated current source. The control loop will regulate the current in the inductor at an accuracy of ±6%. If the output reaches the regulation voltage determined by the resistor divider from the output to the FB pin, the inductor current will be reduced by the voltage regulation loop. In voltage regulation, the output voltage has an accuracy of ±1.5%. For additional operation information, refer to the Block Diagram in Figure 1. The current control loop has two main inputs, determined by the voltages at the analog control pins, CTRL1 and CTRL2. The lower voltage between CTRL1 and CTRL2 determines the regulated output current. The voltages at CTRL1 and CTRL2 are buffered to produce a reference current set by the voltage across an internal 90k resistor. This reference current produces a reference voltage that the average current mode control loop uses to regulate the inductor current as a voltage drop across the external sense resistor, RS. The outputs of the internal buffers are clamped at 1.5V, limiting the control range of the CTRL1 and CTRL2 pins from 0V to 1.5V—corresponding to a 0mV to 51mV range on RS. The FBIN pin provides a third input to the current control loop. This input is dedicated to regulating the input voltage by controlling the inductor current. Inductor current regulation commences when the voltage at the FBIN pin rises higher than 1.206V. Above 1.206V, the inductor current is linearly increased, providing the maximum current, as determined by the voltages at the CTRL pins, when FBIN is at and above 1.26V. When input voltage regulation is not needed, FBIN should be tied to VREF to allow the CTRL pins to control the inductor current. The 2V reference provided on the VREF pin allows the use of a resistor voltage divider to the CTRL1 and CTRL2 pins. The current supplied by the VREF pin should be less than 0.5mA. The error amplifier for the average current mode control loop has a common mode lockout that regulates the inductor current so that the error amplifier is never operated out of the common mode range. The common mode range is from ground to 1.4V below the VIN supply rail. The LT3763 prevents excessive inductor current by triggering overcurrent limit when the inductor current produces a voltage greater than 85mV across the SENSE+ and SENSE– pins. The current is limited on a cycle-by-cycle basis; switching shuts down as soon as the overcurrent level is reached. Overcurrent is not soft-started. The regulated output voltage is set with a resistor divider from the output to the FB pin. The reference for the FB pin is 1.206V. If the output voltage level is high enough to engage the voltage loop, the regulated inductor current will be reduced. If the voltage at the FB pin reaches 1.515V, an internal overvoltage flag is set, shutting down switching for 12μs. The EN/UVLO pin functions as a precision shutdown pin. When the voltage at the EN/UVLO pin is lower than 1.52V, the internal reset flag is asserted and switching is terminated. Full shutdown is guaranteed below 0.5V with a quiescent current of less than 2µA. The EN/UVLO pin has 185mV of hysteresis built in, and a 5µA current source is connected to this pin that allows any amount of hysteresis to be added with a series resistor or resistor divider from VIN. Alternatively, this pin can be tied directly to VIN to reduce the number of off-chip components. During start-up, the SS pin is held low until the internal reset goes low and PWM goes high the first time after a reset event. Once the reset is cleared, the capacitor connected to the soft-start pin is charged with an 11μA current source. Initially, the internal buffers for the CTRL1, CTRL2, and FBIN voltages are limited by the voltage at the soft-start pin, and the inductor current reference slowly increases to the level determined by the lowest voltage of those three pins. The rising threshold for thermal shutdown is set at 165°C with –5°C hysteresis. During thermal shutdown, all switching is terminated, and the part is in reset mode (forcing the SS pin low). The switching frequency is determined by a resistor at the RT pin. This pin is limited to 55µA, which limits the switching frequency to approximately 2MHz when the RT pin is shorted to ground. The LT3763 may also be synchronized to an external clock through the use of the 3763f 13 LT3763 Operation SYNC pin which has precise thresholds at 2.175V and 1.5V for rising and falling edges, respectively. LT3763 also features a PWM driver for LED dimming. PWM_OUT is high when the PWM pin voltage is higher than 2.175V, and low when PWM is lower than 1.5V. Switching is terminated when PWM is lower than 1.5V. PWM should be tied to INTVCC when the PWM function is not needed. The FAULT pin is pulled down to ground when the voltage at FB becomes less than 0.25V which indicates a shortcircuit condition. It is also pulled down to indicate an open-circuit condition when the voltage becomes greater than 1.16V and the inductor current is less than ten percent of the maximum (C/10), or equivalently, when the voltage between SENSE+ and SENSE– is less than 5mV. To avoid jitter when recovering from a fault condition, 50mV hysteresis is employed in the comparators. Additionally, when the inductor current is lower than C/10, the C/10 comparator disables the low side MOSFET regardless of the voltage at FB. The integrated input current and output current monitoring functions of the LT3763 allow users to acquire system information such as the input power and output power. The outputs of the current monitors, IVINMON and ISMON, range from 0V to 1V when the inputs vary from 0V to 50mV. When using 2.5mΩ sense resistors, for example, these current monitoring amplifiers sense from 0A to 20A. To filter out the switching portion of the currents and measure the average current information, the input pins of the input current monitor, IVINP and IVINN, should connect to the sense resistor through two 1k resistors and a capacitor directly between the IVINP and IVINN pins. The capacitance value can be adjusted according to the switching frequency and the ripple magnitude. The output current monitor employs an internal filter to reduce ripple, and it does not require an external filter, but if one is added, the corner frequency should be higher than the switching frequency. The LT3763 also includes an input current limiting function to regulate the input current to a value determined by the RSENSE_IN resistor. When the voltage drop across the RSENSE_IN resistor approaches 50mV, the inductor current is reduced and regulated so that 50mV is maintained across the IVINP and IVINN pins. Applications Information Programming Inductor Current VCTRL 30 •RS IO = where RS is the external sense resistor and IO is the average inductor current, which is equal to the output current. Figure 2 shows the maximum output current versus RS. The maximum power dissipation in the resistor will be: PRS 2 0.05V ) ( = RS Figure 3 plots the power dissipation in RS, and Table 1 lists several resistance values and the corresponding MAXIMUM OUTPUT CURRENT (A) The analog voltage at the CTRL1 pin is buffered and produces a reference voltage, VCTRL, across an internal resistor. The regulated average inductor current is determined by: 30 25 20 15 10 5 0 0 2 4 6 8 10 12 14 16 18 20 RS (mΩ) 3763 F02 Figure 2. RS Value Selection for Regulated Output Current maximum inductor current and sense-resistor power dissipation. Susumu, Panasonic and Vishay offer accurate sense resistors. 3763f 14 LT3763 POWER DISSIPATION (W) Applications Information 1.4 Table 2. Recommended Inductor Manufacturers 1.2 VENDOR WEBSITE 1.0 Coilcraft www.coilcraft.com Sumida www.sumida.com Vishay www.vishay.com 0.8 0.6 Würth Electronics www.we-online.com 0.4 NEC-Tokin www.nec-tokin.com 0.2 0 Switching MOSFET Selection 0 2 4 6 8 10 12 RS (mΩ) 14 16 18 20 3763 F03 Figure 3. Power Dissipation in RS Table 1. Sense Resistor Values MAXIMUM OUTPUT CURRENT (A) RESISTOR, RS (mΩ) POWER DISSIPATION (W) 1 50 0.05 5 10 0.25 10 5 0.50 25 2 1.25 The following parameters are critical in determining the best switching MOSFETs for a given application: total gate charge (QG), on-resistance (RDS(ON)), gate to drain charge (QGD), gate-to-source charge (QGS), gate resistance (RG), breakdown voltages (maximum VGS and VDS) and drain current (maximum ID). The following guidelines provide information to make the selection process easier, and Table 3 lists some recommended parts and manufacturers. For both switching MOSFETs the rated drain current should be greater than the maximum inductor current. Use the following equation to calculate the peak inductor current: Inductor Selection Size the inductor so that the peak-to-peak ripple current is approximately 30% of the output current. The following equation sizes the inductor for best performance: V •V –V 2 IN O O L= 0.3 • fSW •IO • VIN where VO is the output voltage, VIN is the input voltage, IO is the maximum regulated current in the inductor and fSW is the switching frequency. The overcurrent comparator terminates switching when the voltage between the SENSE+ and SENSE– pins exceeds 85mV. The saturation current for the inductor should be at least 20% higher than the maximum regulated current. Recommended inductor manufacturers are listed in Table 2. V •V –V 2 IMAX = IO + IN O O 2 • fSW • L • VIN The rated drain current is temperature dependent, and most data sheets include a table or graph of the rated drain current versus temperature. The rated VDS should be higher than the maximum input voltage (including transients) for both MOSFETs. As for the rated VGS, the signals driving the gates of the switching MOSFETs have a maximum voltage of 5V with respect to the source. However, during start-up and recovery conditions, the gate-drive signals may be as low as 3V. Therefore, to ensure that the LT3763 recovers properly, the maximum threshold voltage should be less than 2V, and for a robust design, ensure that the rated VGS is greater than 7V. Power losses in the switching MOSFETs are related to the on-resistance, RDS(ON); gate resistance, RG; gate-to-drain charge, QGD and gate-to-source charge, QGS. Power lost to the on-resistance is an Ohmic loss, I2RDS(ON), and usually dominates for input voltages less than 15V. Power lost while charging the gate capacitance dominates for voltages 3763f 15 LT3763 Applications Information PLOSS = ohmic loss + transition loss V PLOSS ≈ O •IO2 RDS(ON) • ρT + VIN 7 6 MOSFET POWER LOSS (W) greater than 15V. When operating at higher input voltages, efficiency can be optimized by selecting a high side MOSFET with higher RDS(ON) and lower QG. The total power loss in the high side MOSFET can be approximated by: M1: RDS(ON) = 2.3mΩ, QG = 45.5nC, QGS = 13.8nC, QGD = 14.4nC, RG = 1Ω M2: RDS(ON) = 18mΩ, QG = 10nC, QGS = 4.5nC, QGD = 3.1nC, RG = 3.5Ω Power loss for both MOSFETs is shown in Figure 4. Observe that whereas the RDS(ON) of M1 is eight times lower, the power loss at low input voltages is about equal to that of M2, and at high voltages, it is four times higher. Power loss within the low side MOSFET is almost entirely from the RDS(ON) of the FET. Select the low side FET with the lowest RDS(ON) while keeping the total gate charge QG to 30nC or less. Another power loss related to switching MOSFET selection is the power lost driving the gates. The total gate charge, TRANSITIONAL 3 2 0 OHMIC 0 10 20 40 30 INPUT VOLTAGE (V) 3763 F04a Figure 4a. Power Loss Example for M1 2.5 MOSFET POWER LOSS (W) A good approach to MOSFET sizing is to select a high side MOSFET, then select the low side MOSFET. The trade-off between RDS(ON), QG, and QGS for the high side MOSFET is evident in the following example. VO is equal to 4V. These two N-channel MOSFETs are rated for a VDS of 40V and mounted in the same package, but with 8× different RDS(ON) and 4.5× different QG and QGD: TOTAL 4 1 V •I (QGD +QGS ) • IN OUT • • fSW 5V ( 2 •RG +RPU +RPD ) where rT is a dimensionless temperature dependent factor in the MOSFET’s on-resistance. Using 70°C as the maximum ambient operating temperature, rT is roughly equal to 1.3. RPD and RPU are the LT3763 high side gate driver output impedances: 1.3Ω and 2.2Ω, respectively. 5 2.0 1.5 TOTAL 1.0 TRANSITIONAL 0.5 0 OHMIC 0 10 20 30 40 INPUT VOLTAGE (V) 3763 F04b Figure 4b. Power Loss Example for M2 QG, must be charged and discharged each switching cycle, so the power lost to the charging of the gates is: PGATE = VIN • (QGLG + QGHG) • fSW where QGLG is the low side gate charge and QGHG is the high side gate charge. The majority of this loss occurs in the internal LDO within the LT3763: PLOSS_LDO ≈ (VIN – 5V) • (QGLG + QGHG) • fSW Whenever possible, utilize a switching MOSFET that minimizes the total gate charge to limit the internal power dissipation of the LT3763. Some recommended MOSFETs are listed in Table 3. 3763f 16 LT3763 Applications Information TOP FET BOTTOM FET MANUFACTURER end of every pulse as the decreasing inductor current flows into the output capacitor. Use of a small output capacitor may trigger overvoltage protection through the FB pin. 60 4 20 RJK0853DPB 24 4 5 RJK0368DPA RJK0853DPB Renesas RJK0332DPB www.renesas.com CBOOT Capacitor Selection 48 10 to 35 10 RJK0851DPB VIN VOUT IOUT (V) (V) (A) RJK0851DPB 12 2 to 4 10 FDMS8680 FDMS8672AS Fairchild www.fairchildsemi.com 26 4 20 Si7884BDP 24 4 40 PSMN4R0-30YL RJK0346DPA NXP/Philips www.nxp.com 36 12 10 BSC100N06LS3 BSC100N06LS3 www.infineon.com SiR470DP Vishay www.vishay.com Input Capacitor Selection The input capacitor should be sized at least 2µF for every 1A of output current and placed very close to the high side MOSFET. The loop created by the input capacitor, high side MOSFET, low side MOSFET should be minimized. It should have a ripple current rating equal to half of the maximum output current. Additionally, a small 4.7µF ceramic capacitor should be placed between VIN and ground as close as possible to the VIN pin and the exposed pad of the package for optimal noise immunity. It is recommended that several low ESR (equivalent series resistance) ceramic capacitors be used as the input capacitance, although other capacitors with higher density may be required to reduce board area. Only X5R or X7R capacitors maintain their capacitance over a wide range of operating voltages and temperatures. Output Capacitor Selection The output capacitors need to have very low ESR to reduce output ripple. A minimum of 20µF/A of load current should be used in most designs. The capacitors also need to be surge rated to the maximum output current. To achieve the lowest possible ESR, several low ESR ceramic capacitors should be used in parallel. Many lower output voltage applications benefit from the use of high density POSCAP capacitors, which are easily destroyed when exposed to overvoltage conditions. To prevent this, select POSCAP capacitors that have a voltage rating that is at least 50% higher than the regulated voltage. Note that when dimming, the output voltage increases at the The CBOOT capacitor must be sized no bigger than 220nF and more than 50nF to ensure proper operation of the LT3763. Use 220nF for high current switching MOSFETs with high gate charge. INTVCC Capacitor Selection The bypass capacitor for the INTVCC pin should be larger than 22µF to ensure stability, and it should be connected as close as possible to the exposed pad underneath the package. It is recommended that the ESR be lower than 50mΩ to reduce noise within the LT3763. For driving MOSFETs with gate charges larger than 44nC, use 0.5µF/nC of total gate charge. Soft-Start Unlike conventional voltage regulators, the LT3763 utilizes the soft-start function to control the regulated inductor current instead of the output voltage. The charging current is 11µA and reduces the set current as long as the SS pin voltage is lower than CTRL1 and CTRL2. Output Current Regulation To adjust the regulated load current, an analog voltage is applied to the CTRL1 pin. Figure 5 shows the regulated voltage across the sense resistor for control voltages up to 60 50 VSENSE+ – VSENSE– (mV) Table 3. Recommended Switching FETs 40 30 20 10 0 0 0.5 1.0 VCTRL1 (V) 1.5 2.0 3763 F05 Figure 5. Sense Voltage vs CTRL Voltage 3763f 17 LT3763 Applications Information 2V. Figure 6 shows the CTRL1 voltage created by a voltage divider from VREF to ground. When sizing the resistor divider, please be aware that the VREF pin should have a total load current less than 0.5mA, and that above 1.5V, the control voltage has no effect on the regulated inductor current. Setting CTRL1 to 0V does not automatically stop switching. To disable switching, set PWM pin voltage below 1.5V. Input Current Monitoring Users can monitor the input current at the IVINMON pin, which produces 0V to 1V as the voltage between IVINP and IVINN varies from 0mV to 50mV, as shown in Figure 7. Due to the switching of the high side FET, the input current is noisy and monitoring the average input current requires an external filter with 1k resistors connecting IVINP and IVINN to the input current sense resistor RSENSE_IN. Choose the capacitor for this filter according to the switching frequency so that the noise is reduced by at least a factor of 100. If the frequency is 500kHz, for example, 1µF is sufficient, and higher switching frequencies will require a smaller capacitor. A resistor and capacitor may be connected to IVINMON to further filter the noise. With both input and output current monitoring, the LT3763 enables users to calculate the overall efficiency of the circuit including the losses in the external components. Output Current Monitoring The LT3763 provides users the capability to monitor the output current as a voltage provided at the ISMON pin. The voltage will linearly increase from 0V to 1V as the voltage between SENSE+ and SENSE– increases from 0mV to 50mV as shown in Figure 8. If, for example, a 2.5mΩ resistor is chosen for RS, then a 1V output at ISMON will indicate a 20A output current. A resistor and capacitor may be connected to ISMON to filter noise. Voltage Regulation and Overvoltage Protection The LT3763 uses the FB pin to regulate the output voltage and to provide an overvoltage lockout to avoid high voltage conditions. The regulated output voltage is programmed using a resistor divider from the output to the FB pin (Figure 9). When the output voltage approaches 2.0 VREF LT3763 1.5 VISMON (V) R2 CTRL1 R1 3763 F06 1.0 0.5 Figure 6. Analog Control of Inductor Current 0 2.0 VIVINMON (V) 1.5 0 25 50 75 VSENSE+ – VSENSE– (mV) 100 3763 F08 Figure 8. Output Current Monitoring Voltage vs Output Current Sense Voltage 1.0 VOUT 0.5 LT3763 R2 FB 0 0 25 50 75 VIVINP – VIVINN (mV) 100 3763 F07 Figure 7. Input Current Monitoring Voltage vs Input Current Sense Voltage 18 R1 3763 F09 Figure 9. Output Voltage Regulation and Overvoltage Protection Feedback Connections 3763f LT3763 Applications Information the programmed level (1.206V at the FB pin), the voltage error amplifier overrides CTRL1 to set the inductor current and regulate VOUT. When the output voltage exceeds 125% of the regulated voltage level (1.515V at the FB pin), the internal overvoltage flag is set, terminating switching. The regulated output voltage must be greater than 1.5V and is set by the equation: R2 VOUT = 1.206V 1+ R1 Programming Switching Frequency The LT3763 has an operational switching frequency range between 200kHz and 1MHz. This frequency is programmed with an external resistor from the RT pin to ground. Do not leave this pin open under any condition. The RT pin is also current-limited to 55µA. See Table 4 and Figure 10 for resistor values and the corresponding switching frequencies. Table 4. Switching Frequency SWITCHING FREQUENCY (MHz) RT (kΩ) 1.00 40.2 0.75 53.6 0.50 82.5 0.30 143 0.20 200 Fault Detection Low Current Detection When the inductor current decreases to ten percent of the maximum current, the C/10 comparator will also disable the low side gate driver, so the converter will become non-synchronous and automatically transition into discontinuous conduction mode when the inductor current is low enough relative to the ripple. The low current condition is an essential part of battery charging applications. The LT3763 works well in this application delivering a constant current to the battery as it charges and then automatically reducing the current to a trickle charge as the battery voltage approaches its fully charged value. In this application, the signal at FAULT triggered by the low current detection comparator serves as an indicator that the trickle charge phase of charging the battery has begun. Switching Frequency Synchronization The nominal switching frequency of the LT3763 is determined by the resistor from the RT pin to ground and may be set from 200kHz to 1MHz. The internal oscillator may also be synchronized to an external clock through the SYNC pin. The external clock applied to the SYNC pin must have a logic low below 1.5V and a logic high above 2.175V. The input frequency must be 20% higher than the frequency that would otherwise be determined by the resistor at the RT pin. Input signals outside of these specified parameters will cause erratic switching behavior and subharmonic oscillations. Synchronization is tested at 500kHz with a 200k RT resistor. Operation under other conditions is guaranteed by design. When synchronizing to an external 1.2 1.0 FREQUENCY (MHz) The LT3763 detects that the load has had an open-circuit or short-circuit event indicated by pulling the FAULT pin to ground. These conditions are detected by comparing the voltage at the FB pin to two internal reference voltages. A short-circuit is defined as VFB lower than 0.25V. In an open-circuit condition, the regulated inductor current will charge the output capacitor, the voltage at FB will begin to increase, and the voltage error amplifier will begin to reduce the inductor current. The open-circuit condition will be indicated at FAULT when FB is higher than 1.16V and the inductor current is less than ten percent (C/10) of the maximum value set by the sense resistor RS. The output voltage will be regulated as determined by the resistor divider to the FB pin. 0.8 0.6 0.4 0.2 0 0 50 100 150 200 250 300 350 400 450 500 RT (kΩ) 3763 F10 Figure 10. Frequency vs RT Resistance 3763f 19 LT3763 Applications Information clock, please be aware that there will be a fixed delay from the input clock edge to the edge of the signal at the SW pin. The SYNC pin must be grounded if the synchronization to an external clock is not required. When SYNC is grounded, the switching frequency is determined by the resistor RT. PWM Driver The LT3763 includes a PWM driver for users who want to control the dimming of LEDs connected to the output. The driver will pull up the gate of an external N-channel MOSFET connected to the PWM_OUT pin when the voltage at the PWM pin rises above 2.175V and pull down the gate when the voltage falls below 1.5V. When VPWM is lower than 1.5V, switching is terminated and VC is disconnected from the current regulation amplifier. When VPWM is above 2.175V, the inductor current is regulated to the current programmed by the voltage at the CTRL1, CTRL2, or FBIN pins. The pull-up driver impedance is 2.2Ω, and the pull-down driver impedance is 0.9Ω. The PWM dimming pulse-width should be longer than two switching cycles. VOUT LOAD PWM + 1.5V – The rated VDS for the PWM MOSFET need only be higher than the maximum output voltage. Although this permits a MOSFET choice with a smaller QG specification than that of the switching MOSFETs, it will have little effect on efficiency, because the PWM switching frequency will be much lower than that of the switching MOSFETs. Power lost charging the gate of the PWM MOSFET will naturally be much lower than the power lost charging the switching MOSFETs. RDS(ON) conduction losses in the PWM MOSFET will also be much smaller if the duty cycle of the PWM signal is very low. Like the drivers for the switching MOSFETs, the PWM driver draws power from the INTVCC pin, and the choice of MOSFET should follow the same recommendations for threshold voltage (less than 2V) and rated VGS (at least 7V). Thermal Shutdown The internal thermal shutdown within the LT3763 engages at 165°C and terminates switching and discharges the soft-start capacitor. When the part has cooled to 160°C, the internal reset is cleared and the soft-start capacitor is allowed to charge. Shutdown and UVLO Figure 11. PWM Driver Operation PWM Operation When the voltage at PWM is low, all switching of the high and low side MOSFETS is terminated, and the inductor current will decrease to zero. After PWM increases above the logic threshold, the inductor current ramps up to the regulated value. The ramp time, tD, can be estimated using the following equation: PWM MOSFET Selection PWM_OUT 3763 F11 tD = should be tied to INTVCC so as not to disable switching. L •IO VIN – VO which assumes that the output capacitor does not discharge significantly in the time that PWM is low. When the PWM functionality is not desired, the PWM pin The LT3763 has an internal UVLO that terminates switching, resets all synchronous logic, and discharges the softstart capacitor for input voltages below 4V. The LT3763 also has a precision shutdown at 1.52V on the EN/UVLO pin. Partial shutdown occurs at 1.52V and full shutdown is guaranteed below 0.5V with less than 2µA IQ in the full shutdown state. Below 1.52V, an internal current source provides 5µA of pull-down current to allow for programmable UVLO hysteresis. The following equations determine the voltage-divider resistors for programming the UVLO voltage and hysteresis as configured in Figure 12. R2 = VHYST 5µA 1.52V •R2 R1= VUVLO – 1.52V 3763f 20 LT3763 Applications Information VIN VIN LT3763 VCTRL • 11µA/V 3k L RS R2 MODULATOR EN/UVLO R1 + 3763 F12 gm ERROR AMP Figure 12. UVLO Configuration RC Load Current Derating Using the CTRL2 Pin RV VREF RNTC RNTC RX RNTC RNTC RX CTRL2 R1 (OPTION A TO D) 3763 F13 A B 3763 F14 Figure 14. LT3763 Average Current Mode Control Scheme to the slope compensation ramp determines the stability of the current regulation loop above 50% duty cycle. In the same way, average current mode controllers require the slope of the error voltage to not exceed the PWM ramp slope during the switch off time. Since the closed loop gain at the switching frequency produces the error signal slope, the output impedance of the error amplifier will be the compensation resistor, RC. Use the following equation as a good starting point for compensation component sizing: RV LT3763 – CC The LT3763 is designed specifically for driving high power loads. In high current applications, derating the maximum current based on operating temperature prevents damage to the load. In addition, many applications have thermal limitations that will require the regulated current to be reduced based on load temperature and/or board temperature. To achieve this, the LT3763 uses the CTRL2 pin to reduce the effective regulated current in the load, which is otherwise programmed by the analog voltage at the CTRL1 pin. The load/board temperature derating is programmed using a resistor divider with a temperature dependant resistance (Figure 13). When the load/board temperature rises, the CTRL2 voltage will decrease. When the CTRL2 voltage is lower than voltage at the CTRL1 pin, the regulated current is reduced. R2 LOAD C D Figure 13. Load Current Derating vs Temperature Using NTC Resistor Average Current Mode Control Compensation The use of average current mode control allows for precise regulation of the inductor current and load current. Figure 14 shows the average current mode control loop used in the LT3763, where the regulation current is programmed by a current source and a 3k resistor. To design the compensation network, the maximum compensation resistor needs to be calculated. In current mode controllers, the ratio of the sensed inductor current ramp RC = 1kΩ •1V •L 2nF , CC = •T VO •RS • TSW µs SW where TSW is the switching period, L is the inductance value, VO is the output voltage and RS is the sense resistor. For most applications, a 4.7nF compensation capacitor is adequate and provides excellent phase margin with optimized bandwidth. Please refer to Table 6 for recommended compensation values. Board Layout Considerations Average current mode control is relatively immune to the switching noise associated with other types of control schemes. Nevertheless, the high di/dt loop formed by input capacitors and switching MOSFETS should be minimized. Placing the sense resistor as close as possible to the SENSE+ and SENSE– pins also helps avoid noise issues. Due to sense resistor ESL (equivalent series inductance), 10Ω resistors in series with the SENSE+ and SENSE– pins with a 33nF capacitor placed between the SENSE pins are recommended. Utilizing a good ground plane underneath the switching 3763f 21 LT3763 Applications Information components will minimize interplane noise coupling. To dissipate the heat from the switching components, use a large area for the switching node while keeping in mind that this negatively affects the radiated noise. Table 6. Recommended Compensation Component Values (VCTRL2 = 2V) VIN (V) VO (V) VCTRL1 (V) IL (A) fSW (kHz) L (µH) RS (mΩ) RC (kΩ) CC (nF) 12 4 0.75 5 500 2.2 5 54.9 4.7 12 4 1.50 10 500 2.2 5 54.9 4.7 12 5 1.50 20 250 2.2 2.5 44.2 8.2 60 30 0.15 1 500 10 5 15.4 4.7 60 30 1.20 8 500 10 5 15.4 4.7 Typical Applications 20A, Pulse Width Modulated, Single LED Driver RSENSE_IN 2.5mΩ VIN 10V TO 30V REN1 84.5k CFILT 1µF RFILTA 1k REN2 15.4k IVINP RFILTB 1k IVINN VIN TG EN/UVLO CREF 2.2µF RHOT 45.3k CBOOST 220nF VREF LT3763 CTRL2 RNTC 470k 50k CIN2 100µF CIN1 4.7µF BOOST M1 L1 1.5µH SW INTVCC BG CTRL1 RS 2.5mΩ VOUT 6V, 20A MAXIMUM COUT 220µF ×2 RFAULT 47.5kΩ CVCC 22µF D1 M2 RSA 10Ω RSB 10Ω GND 50Ω 1nF 50Ω 1nF FBIN SENSE+ IVINMON PWMOUT ISMON M3 FAULT PWM SYNC RT RT 82.5k CS 33nF SENSE– FB SS CSS 10nF VC RC 59k CC 4.7nF L1: COILCRAFT XAL1010-152 M1: RENESAS RJK0365 M2: RENESAS RJK0453 M3: IR IRFH6200 RS: VISHAY WSL25122L500FEA RFB1 47.5k RFB2 12.1k 3763 TA02 PWM Dimming PWM 10V/DIV VSW 50V/DIV IL 5A/DIV 5µs/DIV 22 3763 TA02b 3763f LT3763 Typical Applications 1A, Five LED Driver RSENSE_IN 50mΩ VIN 32V TO 60V RFILTA 1k CFILT 1µF IVINP ENABLE CREF 2.2µF RFILTB 1k IVINN VIN EN/UVLO RHOT 45.3k TG VREF LT3763 CTRL2 FBIN SENSE– IVINMON SYNC RT RFAULT 47.5kΩ CVCC 22µF M2 RSA 10Ω CSS 10nF RC 59k CC 4.7nF RSB 10Ω D2 D3 D4 CS 33nF D5 RFB1 287k FB VC COUT 10µF ×2 D1 FAULT SS VOUT 30V, 1A MAXIMUM RS 50mΩ PWMOUT ISMON PWM RT 82.5k L1 100µH GND SENSE+ INTVCC M1 SW BG CTRL1 CBOOST 50nF BOOST INTVCC RNTC 470k 50k CIN2 4.7µF CIN1 1µF L1: COILCRAFT MSS1278-104 M1, M2: RENESAS RJK1054 RS: VISHAY WSL2512R0500FEA RFB2 12.1k 3763 TA03 3763f 23 LT3763 Typical Applications 3.3A, Six-Cell (36V) SLA Battery Charger RSENSE_IN 15mΩ VIN 48V CFILT 1µF RFILTA 1k IVINP ENABLE CREF 2.2µF RFILTB 1k CIN2 47µF CIN1 1µF VIN IVINN EN/UVLO TG VREF BOOST LT3763 INTVCC BG CTRL1 CVCC 22µF M2 FB SS CSS 10nF VC RC 8.06k CC 4.7nF 12V + RFB1 402k FAULT SYNC RT RSB 10Ω CS 33nF PWMOUT ISMON PWM RSA 10Ω + 12V SENSE– IVINMON VOUT 45V, 3.3A MAXIMUM 12V RFAULT 47.5kΩ GND FBIN RS 15mΩ + SENSE+ RT 82.5k L1 12µH SW CTRL2 INTVCC M1 CBOOST 220nF L1: WÜRTH 74471112 M1, M2: INFINEON BSC100N06LS3 M3: VISHAY VN2222LL RS: VISHAY WSL2512R0150 RFB2 12.1k RFB3 178k M3 3763 TA04 36V SLA Battery Charging FAULT 10V/DIV IL 2A/DIV VOUT 50mV/DIV AC-COUPLED 50s/DIV 3763 TA04b 3763f 24 LT3763 Typical Applications 20A, Synchronized, 5V Regulator RSENSE_IN 2.5mΩ VIN 7V TO 30V REN1 44.2k CFILT 1µF RFILTA 1k REN2 15.4k IVINP RFILTB 1k IVINN VIN EN/UVLO CREF 2.2µF RHOT 45.3k TG VREF LT3763 CTRL2 FBIN SENSE– IVINMON RT 121k COUT 220µF ×2 RFAULT 47.5kΩ CVCC 22µF RFB1 38.3k FAULT FB SS CSS 10nF VC RC 59k CC 4.7nF RFB2 12.1k L1: COILCRAFT XAL1010-152 M1: RENESAS RJK0365 M2: RENESAS RJK0453 RS: VISHAY WSL25122L500FEA 3763 TA05 Efficiency vs Load Current 100 VIN = 12V VOUT = 5V ILIMIT = 20A 6 95 EFFICIENCY (%) VOUT (V) RSB 10Ω CS 33nF Output Voltage Load Regulation 8 RSA 10Ω M2 PWMOUT ISMON PWM SYNC RT 500kHz VOUT RS 2.5mΩ 5V, 20A MAXIMUM GND SENSE+ 3V 0V L1 1.5µH SW BG CTRL1 M1 CBOOST 220nF BOOST INTVCC RNTC 470k INTVCC CIN2 100µF CIN1 4.7µF 4 90 2 85 0 80 0 6 12 ILOAD (A) 18 24 3763 TA05b VIN = 12V VOUT = 5V 0 6 12 ILOAD (A) 18 24 3763 TA05c 3763f 25 LT3763 Typical Applications 350W White LED Driver VIN 48V REN1 374k REN2 124k IVINP IVINN VIN EN/UVLO TG VREF CREF 2.2µF BG CTRL1 SENSE+ FBIN SENSE– RFAULT 100k CVCC 22µF M2 ×2 LUMINUS PT-121 CS 1nF RFB1 931k FAULT SYNC RT RT 200k FB SS VC CSS 10nF RC 5k CC 5nF Maximum Output Voltage 3763 TA06 Efficiency vs LED Current 100 30 95 EFFICIENCY (%) VOUT (V) RFB2 30.9k L1: COILTRONICS HC2-6R0 M1, M2: RENESAS RJK0851 RS: VISHAY WSL25125L000 40 20 10 0 VOUT 37V, 10A MAXIMUM RS 5mΩ PWMOUT ISMON PWM 400kHz L1 6µH COUT 10µF ×6 GND IVINMON M1 ×2 SW INTVCC INTVCC CBOOST 220nF BOOST LT3763 CTRL2 3V 0V CIN2 100µF CIN1 4.7µF 90 85 VIN = 48V ILIMIT = 10A 0 3 6 ILED (A) 9 12 3763 TA06b 80 VIN = 48V VOUT = 35V 0 3 6 ILED (A) 9 12 3763 TA06c 3763f 26 LT3763 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. FE Package 28-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1663 Rev I) Exposed Pad Variation EB 9.60 – 9.80* (.378 – .386) 4.75 (.187) 4.75 (.187) 28 27 26 2524 23 22 21 20 1918 17 16 15 6.60 ±0.10 4.50 ±0.10 2.74 (.108) SEE NOTE 4 0.45 ±0.05 EXPOSED PAD HEAT SINK ON BOTTOM OF PACKAGE 6.40 2.74 (.252) (.108) BSC 1.05 ±0.10 0.65 BSC RECOMMENDED SOLDER PAD LAYOUT 4.30 – 4.50* (.169 – .177) 0.09 – 0.20 (.0035 – .0079) 0.50 – 0.75 (.020 – .030) NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS 2. DIMENSIONS ARE IN MILLIMETERS (INCHES) 3. DRAWING NOT TO SCALE 1 2 3 4 5 6 7 8 9 10 11 12 13 14 0.25 REF 1.20 (.047) MAX 0° – 8° 0.65 (.0256) BSC 0.195 – 0.30 (.0077 – .0118) TYP 0.05 – 0.15 (.002 – .006) FE28 (EB) TSSOP REV I 0211 4. RECOMMENDED MINIMUM PCB METAL SIZE FOR EXPOSED PAD ATTACHMENT *DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.150mm (.006") PER SIDE 3763f 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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 27 LT3763 Typical Application 70W, Solar Energy Harvester with Maximum Power Point Regulation PANEL VOLTAGE UP TO 60V 37V VIN REG POINT RSENSE_IN 10mΩ D1 CFILT 1µF RFILTA 1k D2 IVINP ENABLE Dn RFILTB 1k IVINN VIN EN/UVLO CREF 2.2µF RHOT 45.3k TG VREF LT3763 CTRL2 VREF CTRL1 RFAULT 47.5kΩ CVCC 22µF RSA 10Ω M2 3.6V RSB 10Ω PWMOUT ISMON PWM SYNC RT CS 33nF SENSE– IVINMON RT 82.5k VOUT RS 10mΩ 14V MAXIMUM + SENSE+ INTVCC L1 12µH GND FBIN RFBIN2 12.1k M1 SW BG RFBIN1 348k CBOOST 100nF BOOST INTVCC RNTC 470k CIN2 100µF CIN1 4.7µF RFB1 121k FAULT FB SS CSS 10nF VC RC 26.1k CC 4.7nF L1: COILCRAFT MSS1278-123 M1, M2: INFINEON BSC100N06LS3 M3: VISHAY VN2222LL RS: VISHAY WSL2512R0100FEA RFB2 12.1k RFB3 182k M3 3763 TA07 Solar Powered SLA Battery Charging FAULT 10V/DIV VIN 500mV/DIV AC-COUPLED IL 2A/DIV VOUT 50mV/DIV 50s/DIV 3763 TA07b Related Parts PART NUMBER DESCRIPTION COMMENTS LT3743 Synchronous Step-Down LED Driver Controller 92% Efficiency, IOUT to 20A, VIN: 5.5V to 36V, IQ = 2mA, ISD < 1µA, 4mm × 5mm QFN-28, TSSOP-28E LT3741 Synchronous Step-Down LED Driver Controller 94% Efficiency, IOUT to 20A, VIN: 6V to 36V, IQ = 1.8mA, ISD < 1µA, 4mm × 4mm QFN-20, TSSOP-20E LT3791 Synchronous Buck-Boost LED Driver Controller 98.5% Efficiency, IOUT to 25A, VIN: 4.7V to 60V, TSSOP-38E 3763f 28 Linear Technology Corporation LT 1012 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LINEAR TECHNOLOGY CORPORATION 2012