LT3932/LT3932-1 36V, 2A Synchronous Step-Down LED Driver FEATURES DESCRIPTION 1.5% LED Current Regulation nn 1.2% Output Voltage Regulation nn 5000:1/10000+:1 PWM Dimming at 100Hz (LT3932/LT3932-1) nn 128:1 Internal PWM Dimming nn Spread-Spectrum Frequency Modulation nn Silent Switcher(R) Architecture for Low EMI nn 3.6V to 36V Input Voltage Range nn 0V to 36V LED String Voltage nn 200kHz to 2MHz with SYNC Function nn 99.9% Maximum Duty Cycle nn 20:1 Analog or Duty Cycle LED Current Control nn Open/Short LED Protection and Fault Indication nn Accurate LED Current Sense with Monitor Output nn Programmable UVLO nn Thermally Enhanced 28-Pin (4mm x 5mm) QFN The LT(R)3932 , featuring the Silent Switcher(R)architecture to minimize EMI/EMC emissions, utilizes fixed-frequency, peak current control and provides PWM dimming for a string of LEDs. The LED current is programmed by an analog voltage or the duty cycle of pulses at the CTRL pin. An output voltage limit can be set with a resistor divider to the FB pin. APPLICATIONS Additional features include an LED current monitor, an accurate EN/UVLO pin threshold, open-drain fault reporting for open-circuit and short-circuit load conditions, and thermal shutdown. nn The switching frequency is programmable from 200kHz to 2MHz by an external resistor at the RT pin or by an external clock at the SYNC/SPRD pin. With the optional spread spectrum frequency modulation enabled, the frequency varies from 100% to 125% to reduce EMI. The LT3932 also includes a driver for an external, high side PMOS for PWM dimming and an internal PWM signal generator for analog control of PWM dimming when an external signal is not available. The LT3932-1 permits higher dimming ratios. Automotive Lighting Industrial and General Purpose Lighting nn Machine Vision Systems nn nn All registered trademarks and trademarks are the property of their respective owners. Protected by U.S. Patents including 7199560, 7321203, 9596728, 9642200 and other patents pending. TYPICAL APPLICATION 2A LED Driver with Internal PWM Dimming INTVCC VIN 20V VIN 274k 10F SW EN/UVLO 2x1F Internal PWM Dimming BST 110k FB LT3932 10k VREF 100k 100k SW 20V/DIV VOUT 30.1k 2.2F 22nF 8.2H COUT 100F 2A MAX IL 1A/DIV GND CTRL PWM ISP 50m INTVCC 2.2F ISN 100k FAULT 45.3k 2MHz 100nF ISMON ILED 1A/DIV PWM = 1.078V 2s/DIV (8% PWM DUTY RATIO) PWMTG FAULT SYNC/SPRD SS RT RP PWMTG 10V/DIV 3932 TA01b ISMON VC 28.7k 7.8kHz 162k 9V 10nF 3932 TA01a Rev B Document Feedback For more information www.analog.com 1 LT3932/LT3932-1 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) GND BST INTVCC VIN CTRL EN/UVLO TOP VIEW VIN, EN/UVLO.............................................................40V ISP, ISN, and VOUT.....................................................40V ISP - ISN................................................................0.3V CTRL and FB.............................................................3.3V PWM, SYNC/SPRD, and FAULT....................................6V SS and VC.................................................................3.3V SW, BST, INTVCC, VREF, ISMON, PWMTG, RT, and RP................................................................ (Note 2) Operating Junction Temperature Range (Notes 3, 4) LT3932E/LT3932I............................... -40C to 125C LT3932H............................................. -40C to 150C Storage Temperature Range................... -65C to 150C 28 27 26 25 24 23 VREF 1 22 GND SS 2 21 VIN VC 3 FB 4 20 VIN 19 SW 29 GND ISP 5 ISN 6 ISMON 7 16 VIN FAULT 8 15 GND 18 SW 17 VIN VOUT PWMTG PWM SYNC/SPRD RT RP 9 10 11 12 13 14 UFD PACKAGE 28-LEAD (4mm x 5mm) PLASTIC QFN JA = 25C/W (MEASURED ON DC2286A) 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 LT3932EUFD#PBF LT3932EUFD#TRPBF 3932 28-Lead (4mm x 5mm) Plastic QFN -40C to 125C LT3932IUFD#PBF LT3932IUFD#TRPBF 3932 28-Lead (4mm x 5mm) Plastic QFN -40C to 125C LT3932HUFD#PBF LT3932HUFD#TRPBF 3932 28-Lead (4mm x 5mm) Plastic QFN -40C to 150C LT3932EUFD-1#PBF LT3932EUFD-1#TRPBF 39321 28-Lead (4mm x 5mm) Plastic QFN -40C to 125C LT3932IUFD-1#PBF LT3932IUFD-1#TRPBF 39321 28-Lead (4mm x 5mm) Plastic QFN -40C to 125C LT3932HUFD-1#PBF LT3932HUFD-1#TRPBF 39321 28-Lead (4mm x 5mm) Plastic QFN -40C to 150C Contact the factory for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. Tape and reel specifications. Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix. ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 12V, VEN/UVLO = 5V unless otherwise noted. PARAMETER CONDITIONS MIN Input Voltage Range VIN Pin Quiescent Current TYP 3.6 EN/UVLO = 2V, Not Switching EN/UVLO = 300mV, Shutdown EN/UVLO Threshold (Falling) UNITS 36 V 2.2 2.7 2 mA A 1.15 1.21 V l 1.09 MAX EN/UVLO Rising Hysteresis 20 mV EN/UVLO Pin Hysteresis Current 4 A 2 Rev B For more information www.analog.com LT3932/LT3932-1 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 12V, VEN/UVLO = 5V unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS 1.975 1.980 2 1.998 2.020 2.016 V V Reference VREF Voltage IVREF = 0A IVREF = 500A VREF Pin Current Limit VREF = 1.9V, Current Out of Pin l 2 mA LED Current Regulation CTRL-Off Threshold (Falling) l 200 CTRL-Off Rising Hysteresis 218 228 20 -100 mV mV CTRL Pin Current VCTRL = 2V Sense Voltage (VISP-VISN) (Analog Input) VCTRL = 1.5V (100%), VIN = 36V, VISP = 24V VCTRL = 750mV (50%), VIN = 36V, VISP = 24V VCTRL = 300mV (5%), VIN = 36V, VISP = 24V ISP Pin Current VIN = 36V, VISP = 24V, VCTRL = 2V, Current Into Pin 50 A ISN Pin Current VIN = 36V, VISN = 23.9V, VCTRL = 2V, Current Into Pin 50 A ISP/ISN Common Mode Range VIN = 36V (Note 5) Current Error Amplifier Transconductance VIN = 36V, VISP = 24V l l l 98.5 48.5 4 100 50 5 0 100 nA 101.5 51.5 6 mV mV mV 36 200 V A/V Duty Cycle Control of LED Current Sense Voltage (VISP-VISN) (Duty Cycle Input) CTRL Duty = 75% (100%), VIN = 36V, VISP = 24V CTRL Duty = 37.5% (50%), VIN = 36V, VISP = 24V CTRL Duty = 15% (5%), VIN = 36V, VISP = 24V 99 49 4 CTRL Pulse Input High (VIH) 100 50 5 101 51 6 1.6 V CTRL Pulse Input Low (VIL) 0.4 CTRL Pulse Input Frequency Range mV mV mV 100 V 1000 kHz 1.012 V Voltage Regulation FB Regulation Voltage VISP = VISN = 6V, VCTRL = 2V FB Pin Current VFB = 1V l 0.988 1.000 -100 Voltage Error Amplifier Transconductance 100 480 nA A/V Power Stage Peak Current Limit 3.0 3.6 Minimum Off-Time (Note 6) 55 Minimum On-Time (Note 6) 4.2 A ns 55 ns Bottom Switch On-Resistance 90 m Top Switch On-Resistance 90 m Oscillator Programmed Switching Frequency (fSW) RT = 45.3k, VSYNC/SPRD = 0V RT = 523k, VSYNC/SPRD = 0V Spread Spectrum Frequency Range RT = 45.3k, VSYNC/SPRD = 3.3V RT = 523k, VSYNC/SPRD = 3.3V RT Pin Current Limit VRT = 0V, Current Out of Pin l l 1900 180 1900 180 2100 230 kHz kHz 2650 290 kHz kHz 34 SYNC/SPRD Threshold (Rising) 1.4 SYNC/SPRD Falling Hysteresis SYNC/SPRD Pin Current 2000 200 A 1.5 220 VSYNC/SPRD = 3.3V -100 V mV 100 nA Soft-Start SS Pin Charging Current VSS = 0V 20 A Rev B For more information www.analog.com 3 LT3932/LT3932-1 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 12V, VEN/UVLO = 5V unless otherwise noted. PARAMETER CONDITIONS SS Pin Discharging Current VSS = 2V MIN TYP MAX UNITS 1.25 A SS Lower Threshold (Falling) 200 mV SS Higher Threshold (Rising) 1.7 V Fault Detection Open-Circuit Threshold (FB Rising) l 930 Open-Circuit Falling Hysteresis 950 970 55 Short-Circuit Threshold (FB Falling) l 180 Short-Circuit Rising Hysteresis 200 mV 220 50 FAULT Pull-Down Current VFAULT = 200mV, VFB = 0V 100 FAULT Leakage Current VFAULT = 3.3V, VFB = 700mV -100 mV mV mV A 100 nA Overvoltage Protection FB Overvoltage Threshold (FB Rising) 1.050 FB Overvoltage Falling Hysteresis V 48 mV LED Current Monitor ISMON Voltage VISP - VISN = 100mV (100%), VISP = 12V VISP - VISN = 10mV (10%), VISP = 12V 0.965 80 1.000 100 1.030 120 10 11 V mV PWM Driver PWMTG Gate Drive (VOUT - VPWMTG) VOUT = 12V, VPWM = 2V PWM Threshold (Rising) VOUT = 12V, VRP = 0V 1.4 V PWM Falling Hysteresis VOUT = 12V, VRP = 0V 200 mV PWM Pin Current VPWM = 2V PWM to PWMTG Propagation Delay Turn-On Turn-Off CPWMTG = 2.2nF (Connected from VOUT to PWMTG), VOUT = 12V l -100 100 100 100 V nA ns ns Analog Control for PWM Dimming PWM Voltage for 100% Dimming RP = 28.7k, VREF = 2V PWM Voltage for 0% Dimming RP = 28.7k, VREF = 2V PWM Dimming Accuracy RP = 28.7k, VREF = 2V, VPWM = 1.1V RP = 28.7k, VREF = 2V, VPWM = 1.9V PWM Dimming Frequency RP = 28.7k, RT = 45.3k, VSYNC/SPRD = 0V RP = 332k, RT = 45.3k, VSYNC/SPRD = 0V RP Pin Current Limit VRP = 0V, Current Out of Pin 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: Do not apply a positive or negative voltage source to these pins, otherwise permanent damage may occur. Note 3: The LT3932E is guaranteed to meet performance specifications from 0C to 125C junction temperature. Specifications over the -40C to 125C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. The LT3932I is guaranteed to meet performance specifications over the -40C to 125C operating junction temperature range. The LT3932H is guaranteed over the -40C to 150C operating junction temperature range. Operating lifetime is derated for junction temperatures greater than 125C. 4 2.00 l l V 0.99 V 7.8 87 10 90 12.4 93 % % 7.42 116 7.81 122 8.20 128 kHz Hz 60 A Note 4: 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 5: The current sense error amplifier is tested with VISP = 36V, and separately, with VISN = 0V. Note 6: The MIN on and off times are guaranteed by design and are not tested. Rev B For more information www.analog.com LT3932/LT3932-1 TYPICAL PERFORMANCE CHARACTERISTICS EN/UVLO Pin Current VIN UVLO Threshold (Rising) 5.5 3.6 1.3 5.1 3.4 1.2 1.1 1.0 VIN VOLTAGE (V) 1.4 EN/UVLO CURRENT (A) EN/UVLO VOLTAGE (V) EN/UVLO Threshold (Falling) VIN = 12V, unless otherwise noted. 4.7 4.3 0 3.5 -50 -25 25 50 75 100 125 150 TEMPERATURE (C) 0 3932 G01 2.6 -50 -25 25 50 75 100 125 150 TEMPERATURE (C) VIN Shutdown Current 5.0 INTVCC Voltage VIN Quiescent Current 3.5 3.5 INTVCC VOLTAGE (V) VIN CURRENT (mA) VIN CURRENT (nA) 3.4 4.0 1 3.0 2.5 2.0 1.5 1.0 0.1 0 0 -50 -25 25 50 75 100 125 150 TEMPERATURE (C) VEN/UVLO = 1V 0 3.2 3.1 3.0 2.8 -50 -25 25 50 75 100 125 150 TEMPERATURE (C) INTVCC Load Regulation VREF Voltage 2.02 2.02 3.36 2.01 2.01 2.00 1.99 1.98 3.30 3.28 2.03 VREF VOLTAGE (V) 3.38 VREF VOLTAGE (V) 2.03 3.32 0 3 6 9 12 INTVCC CURRENT (mA) 15 25 50 75 100 125 150 TEMPERATURE (C) 3932 G06 3.40 3.34 0 3932 G05 3932 G04 INTVCC VOLTAGE (V) 3.3 2.9 0.5 VEN/UVLO = 0.3V 0.01 -50 -25 25 50 75 100 125 150 TEMPERATURE (C) 3932 G03 4.5 1k 10 0 3932 G02 10k 100 3.0 2.8 3.9 0.9 -50 -25 3.2 1.97 -50 -25 VREF Load Regulation 2.00 1.99 1.98 0 25 50 75 100 125 150 TEMPERATURE (C) 3932 G08 3932 G07 1.97 0 0.4 0.8 1.2 1.6 VREF CURRENT (mA) 2 3932 G09 Rev B For more information www.analog.com 5 LT3932/LT3932-1 TYPICAL PERFORMANCE CHARACTERISTICS INTVCC and VREF UVLO Threshold 3.3 2.02 3.0 Minimum On-Time and Off-Time 75 MINIMUM OFF-TIME MINIMUM ON-TIME 65 2.7 150C 2.00 25C 1.99 2.4 TIME (ns) 2.01 VOLTAGE (V) VREF VOLTAGE (V) VREF Line Regulation 2.03 2.1 1.98 6 12 18 24 VIN VOLTAGE (V) 45 35 1.5 0 55 1.8 -50C 1.97 VIN = 12V, unless otherwise noted. 30 1.2 -50 -25 36 INTVCC VREF 0 25 -50 -25 25 50 75 100 125 150 TEMPERATURE (C) 3932 G10 0 25 50 75 100 125 150 TEMPERATURE (C) 3932 G11 3932 G12 SS Thresholds SS Pin Pull-Up Current RP and RT Pin Current Limit 70 2.0 24 23 1.6 50 40 SS VOLTAGE (V) 22 SS CURRENT (A) CURRENT (A) 60 21 20 19 18 30 20 -50 -25 0.8 0.4 16 -50 -25 25 50 75 100 125 150 TEMPERATURE (C) 0 0 -50 -25 25 50 75 100 125 150 TEMPERATURE (C) 3932 G13 PWM Duty Ratio 220 RT = 523k 200 1600 110 INTERNAL PWM RT = 45.3k 100 90 80 DUY RATIO (%) 240 PWM FREQUENCY (kHz) RT = 45.3k 1800 25 50 75 100 125 150 TEMPERATURE (C) 3932 G15 Internal PWM Frequency 10 260 2000 0 3932 G14 SW Frequency 2200 SW FREQUENCY (kHz) LOWER RISING LOWER FALLING UPPER RISING UPPER FALLING 17 RP Current RT Current 0 1.2 1 70 60 50 40 30 20 10 1400 -50 -25 180 0 25 50 75 100 125 150 TEMPERATURE (C) 3932 G16 6 0.1 10k 0 EXTERNAL PWM 100k RP RESISTANCE () 1M 3932 G17 -10 0 0.5 1 1.5 2 PWM VOLTAGE (V) 2.5 3 3932 G18 Rev B For more information www.analog.com LT3932/LT3932-1 TYPICAL PERFORMANCE CHARACTERISTICS LED Current (Digital CTRL) 100 90 90 80 80 70 70 VISP - VISN (mV) 100 VISP - VISN (mV) 110 60 50 40 30 50 40 30 20 10 10 0 0 0.25 0.50 0.75 1 1.25 1.50 1.75 CTRL VOLTAGE (V) -10 2 0 240 180 150 120 90 150 120 90 30 30 0 4.8 99.6 100.0 100.4 100.8 101.2 VISP - VISN (mV) 4.9 3932 G22 5.3 49.6 30 50 70 DUTY RATIO (%) 0.5 90 3932 G25 51.0 2 LEDs (APPROX. 6V) 2MHz SW FREQUENCY VCTRL = 735mV 49.2 48.8 48.0 0 50 3932 G23 48.4 2.4 10 1.0 0 5.4 6 12 18 24 VIN VOLTAGE (V) 30 36 3932 G26 250 300 3932 G24 LED Current vs VOUT 50.2 49.8 49.4 0 100 150 200 VISP - VISN (mV) 50.6 VISP - VISN (mV) 3.6 VISP - VISN (mV) PEAK SW CURRENT (A) 50.0 2.0 5 5.1 5.2 VISP - VISN (mV) 1.02 1.5 LED Current Line Regulation Peak SW Current Limit 4.0 2.8 1.01 2.0 300 UNITS VCTRL = 300mV 180 60 3.2 0.99 1 FB VOLTAGE (V) ISMON Voltage 210 60 99.2 0.98 3932 G21 ISMON VOLTAGE (V) 210 0 98.8 155C 25C -50C 270 NUMBER OF UNITS NUMBER OF UNITS 240 0 0.97 12.5 25 37.5 50 62.5 75 87.5 100 CTRL DUTY RATIO (%) LED Current (5% Regulation) 300 300 UNITS VCTRL = 1.5V 155C 25C -50C 50 3932 G20 LED Current (100% Regulation) 270 75 25 3932 G19 300 VCTRL = 2V 100 60 20 0 LED Voltage Limit 125 VISP - VISN (mV) LED Current (Analog CTRL) 110 -10 VIN = 12V, unless otherwise noted. 49.0 VIN = 36V VCTRL = 750mV 2MHz SW FREQUENCY 0 6 12 18 24 VOUT VOLTAGE (V) 30 36 3932 G27 Rev B For more information www.analog.com 7 LT3932/LT3932-1 TYPICAL PERFORMANCE CHARACTERISTICS FB OPENLED Threshold RISING FALLING 1.05 FB SHORTLED Threshold 1.00 0.95 0.90 Power Switch On-Resistance 300 RISING FALLING 0.35 FB VOLTAGE (V) FB VOLTAGE (V) 0.40 0.30 0.25 0.20 0.15 0.85 0.80 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (C) 0.10 -50 -25 0 2 LEDs (APPROX. 6V, 1A) 20 25 30 VIN VOLTAGE (V) 35 40 5 LEDs (APPROX. 15V) 4 LEDs (APPROX. 12V) 1.01 PWMTG Voltage 0 400 800 1200 ILED (mA) 1600 0.97 -50 -25 2000 10 9 8 VOUT = 20V VPWM = 2V 25 50 75 100 125 150 TEMPERATURE (C) 0 25 50 75 100 125 150 TEMPERATURE (C) 3932 G33 FB OVLO Threshold 1.100 TURN-ON TURN-OFF RISING FALLING 1.050 200 175 150 125 1.000 0.950 100 CPWMTG = 2.2nF (X7R) DATA INCLUDES CAPACITANCE VARIATION WITH TEMPERATURE 75 50 -50 -25 VCTRL = 2V VISP - VISN = 0V 3932 G32 FB VOLTAGE (V) PROPAGATION DELAY (ns) 11 0 0.99 PWM Driver Propagation Delay 250 225 7 -50 -25 1.00 0.98 VIN = 24V 2MHz SW FREQUENCY 3932 G31 12 VOUT - VPWMTG (V) Regulated FB Voltage 90 80 25 50 75 100 125 150 TEMPERATURE (C) 1.02 85 15 0 3932 G30 FB VOLTAGE (V) EFFICIENCY (%) EFFICIENCY (%) 90 85 0 25 50 75 100 125 150 TEMPERATURE (C) 3932 G35 3932 G34 8 0 -50 -25 25 50 75 100 125 150 TEMPERATURE (C) 95 95 10 100 Efficiency vs ILED 100 400kHz 2MHz 5 150 3932 G29 Efficiency vs VIN 80 200 50 3932 G28 100 TOP SWITCH BOTTOM SWITCH 250 RESISTANCE (mOhm) 1.10 VIN = 12V, unless otherwise noted. 0.900 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (C) 3932 G36 Rev B For more information www.analog.com LT3932/LT3932-1 TYPICAL PERFORMANCE CHARACTERISTICS C/10 Threshold RISING FALLING 16 14 SW CURRENT (A) VISP - VISN (mV) DA Current Limit 12 10 200 2.4 160 2.3 2.2 2.1 8 6 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (C) 2.0 -50 -25 NUMBER OF UNITS 120 80 0 25 50 75 100 125 150 TEMPERATURE (C) 0 8.6 9 9.4 9.8 10.2 10.6 11.0 11.4 11.8 PWM DUTY RATIO (%) 3932 G38 Internal PWM Duty Ratio (90%) 160 250 UNITS VPWM = 1.1V 150C 25C -50C 40 3932 G37 200 Internal PWM Duty Ratio (10%) 2.5 NUMBER OF UNITS 18 VIN = 12V, unless otherwise noted. 3932 G39 Input Voltage Transient Response Input Voltage Transient Response 250 UNITS VPWM = 1.9V 150C 25C -50C VIN 10V/DIV VIN 10V/DIV ILED 100mA/DIV ILED 100mA/DIV 120 80 40 1ms/DIV 0 88.6 89 89.4 89.8 90.2 90.6 91.0 91.4 91.8 PWM DUTY RATIO (%) 3932 G41 1ms/DIV 3932 G42 FRONT PAGE APPLICATION 15V TO 25V INPUT VOLTAGE STEP 3 LEDs (APPROX. 9V) FRONT PAGE APPLICATION 25V TO 15V INPUT VOLTAGE STEP 3 LEDs (APPROX. 9V) Start-Up with 10% Internal PWM Start-Up with 90% Internal PWM 3932 G40 Turn-On and Turn-Off VIN 20V/DIV VIN 20V/DIV VIN 20V/DIV VOUT 5V/DIV VOUT 5V/DIV VOUT 5V/DIV ILED 500mA/DIV ILED 500mA/DIV ILED 500mA/DIV 5ms/DIV FRONT PAGE APPLICATION 3 LEDs (APPROX. 9V) 3932 G43 5ms/DIV 3932 G44 FRONT PAGE APPLICATION WITH PWM = 1.1V 3 LEDs (APPROX. 9V) 5ms/DIV 3932 G45 FRONT PAGE APPLICATION WITH PWM = 1.9V 3 LEDs (APPROX. 9V) Rev B For more information www.analog.com 9 LT3932/LT3932-1 PIN FUNCTIONS VIN: Input Voltage Pins. These pins supply power to the internal, high performance analog circuitry, and they supply the inductor current when the internal high side power switch is on. Connect capacitors between these pins and GND and see Selecting and Placing the Input Capacitors in Applications Information for advice regarding their placement. EN/UVLO: Enable and Undervoltage Lockout Pin. A voltage at this pin greater than 1.15V will enable switching, and a voltage less than 300mV is guaranteed to shut down the internal current bias and sub-regulators. A resistor network between this pin and VIN can be used to set the pin voltage and automatically lockout the part when VIN is below a certain level. No internal components pull up or down on this pin, so it requires an external voltage bias for normal operation. This pin may be tied directly to VIN. INTVCC: Internally Regulated, Low-Voltage Supply Pin. This pin provides the power for the converter switch gate drivers. Do not force any voltage on this pin, but bypass it with a 2.2F capacitor to GND. VREF: Reference Voltage Pin. This pin provides a buffered 2V reference capable of 1mA drive. It can be used to supply resistor networks for setting the voltages at the CTRL and PWM pins. Bypass with a 2.2F capacitor to GND. FB: Feedback Pin. When the voltage at this pin is near 1V, the regulated current is automatically reduced from the programmed value. A resistor network between this pin and VOUT can be used to set a limit for the output voltage. If the voltage at the FB pin reaches 1.05V, an overvoltage lockout comparator disables switching. FAULT: Fault Pin. Connect to INTVCC through a resistance of 100k. When the FB pin voltage is less than 200mV, an internal switch pulls this pin low to indicate a short-circuit. When FB is greater than 950mV and the voltage between ISP and ISN is simultaneously less than 10mV, the switch pulls this pin low to indicate an open-circuit. ISP: Positive Current Sense Pin. This pin is one of the inputs to the internal current sense error amplifier. It should be connected to the positive side of the external sense resistor. SS: Soft-Start Pin. At startup and recovery from fault conditions, a 20A current charges the capacitor and the FB voltage tracks the rising voltage at this pin until the load current reaches its programmed level. Typical values for the capacitor are 10nF to 100nF. A resistor from SS to INTVCC is used to select one of several fault modes. See Soft-Start and Fault Modes in Applications Information for more details. ISN: Negative Current Sense Pin. This pin is one of the inputs to the internal current sense error amplifier. It should be connected to the negative side of the external sense resistor. VC: Compensation Pin. A capacitor connected from this pin to GND stabilizes the current and voltage regulation. See Stabilizing the Regulation Loop in the Applications Information section for more details. ISMON: Output Current Monitoring Pin. This pin provides a buffered voltage output equal to 10mV for every 1mV between ISP and ISN. SW: Switch Pins. These two pins are internally connected to the power devices and drivers. They should always be tied together. In normal operation, the voltage of these pins will switch between the input voltage and zero at the programmed frequency. Do not force any voltage on these pins. CTRL: Control Pin. An analog voltage from 250mV to 1.25V at this pin programs the regulated voltage between ISP and ISN (and therefore, the regulated current supplied to the load). Alternatively, a digital pulse at this pin with duty cycle from 12.5% to 62.5% can be used to program the regulated voltage. Below 200mV or 10% duty cycle, the CTRL pin voltage disables switching. For more detail, see Regulated LED Current in Typical Performance Curves and Programming LED Current with the CTRL Pin in Applications Information. 10 RT: Timing Resistor Pin. A resistor from this pin to GND programs the switching frequency between 200kHz and 2MHz. Do not leave this pin open. Rev B For more information www.analog.com LT3932/LT3932-1 PIN FUNCTIONS SYNC/SPRD: Synchronization Pin. To override the programmed switching frequency, drive this pin with an external clock having a frequency between 200kHz and 2MHz. Even when using the external clock, select an RT resistor that corresponds to the desired switching frequency. Tie the pin to INTVCC to enable spread spectrum frequency modulation. This pin should be tied to GND when not in use. BST: Boost Pin. This pin supplies the high side power switch driver. Connect a 22nF capacitor between this pin and SW, and connect a diode from INTVCC to BST to charge the capacitor when the SW pin is low. PWM: PWM Input Pin. With the RP pin tied to GND, drive this pin with a digital pulse to control PWM dimming of the LEDs. Alternatively, set the voltage of this pin between 1V and 2V to generate an internal pulse with duty ratio between 0% and 100%. In this case, place a 1F bypass capacitor between this pin and GND. Tie this pin high when PWM dimming is not required. PWMTG: PWM Driver Output Pin. This pin can drive the gate of an external, high side PMOS device for PWM dimming of LEDs. Do not force any voltage on this pin. RP: PWM Resistor Pin. Connect a resistor from this pin to GND to set the frequency of the internal PWM signal. Do not use a resistor larger than 1M. If using an external PWM pulse for LED dimming, tie this pin to GND. VOUT: PWM Driver Supply Pin. This pin supplies an internal regulator for the driver of the external PMOS device. Tie this pin to the output voltage even if dimming is not required. GND: Ground Pins. These must be soldered to the ground plane of the circuit board. Rev B For more information www.analog.com 11 LT3932/LT3932-1 BLOCK DIAGRAM D1 CVCC 25 26 REN2 24 INTVCC VIN CIN VIN INTERNAL VCC REGULATOR AND UVLO EN/UVLO 27 20 21 R VREF 2V REFERENCE Q SW 18 SYNCHRONOUS CONTROLLER PEAK CURRENT COMPARATOR 19 BOTTOM SWITCH DRIVER DA CURRENT + - + LIMIT 8.2H RT VOUT 10 RT CIN VIN TOP SWITCH DRIVER S 1 17 22nF REN1 CREF 16 BST 1.4V SYNC/SPRD 11 14 200kHz TO 2MHz OSCILLATOR - 4.7F + S/H VOUT - 10V REGULATOR S/H 50m CURRENT REGULATION AMPLIFIER gm = 200S PWMTG PWMTG DRIVER 13 - + 3k - A/D DETECTOR + CONTROL BUFFER + + - + CTRL 28 - 1.25V PWM 12 3k ISMON INTERNAL PWM SIGNAL 7 30k 250mV + - 10x VOLTAGE REGULATION AMPLIFIER gm = 480S ISN 6 ISP + + - 5 4 1.0V 950mV 20A INTVCC - - 1.25A 200mV GND 15 22 23 29 SS VC 2 3 RSS CSS 12 RFB1 RFAULT FAULT + FAULT LOGIC RFB2 FB 8 FAULT COMPARATORS FAULT LOGIC + RP 9 3923 BD INTVCC CC Rev B For more information www.analog.com LT3932/LT3932-1 OPERATION The LT3932 is a step-down LED driver that utilizes fixedfrequency, peak-current control to accurately regulate the current through a string of LEDs. It includes two power switches and their drivers. The switches connect an external inductor at the SW pin alternately to the input supply and then to ground. The inductor current rises and falls accordingly and the peak current can be regulated by adjusting the duty ratio of the power switches through the combined effect of the other circuit blocks. The synchronous controller ensures the power switches do not conduct at the same time, and a programmable oscillator turns on the top switch at the beginning of each switching cycle. The frequency of this oscillator is set by an external resistor at the RT pin and can be overridden by external pulses at the SYNC/SPRD pin. The SYNC/SPRD pin can also be used to command spread spectrum frequency modulation (SSFM), which reduces radiated and conducted electromagnetic interference (EMI). The top switch is turned off by the peak current comparator which waits during the on-time for the increasing inductor current to exceed the target set by the voltage at the VC pin. This target is modified by a signal from the oscillator which stabilizes the inductor current. A capacitor at the VC pin is necessary to stabilize this regulation loop. The target for the inductor current is derived from the desired LED current programmed by the voltage at the CTRL pin. The analog-to-digital detector and the control buffer convert either a DC voltage or digital pulses at the CTRL pin into the input for the current regulation amplifier. The other input to this amplifier comes from the ISP and ISN pin voltages. An external current sense resistor between these pins should be placed in series with the string of LEDs such that the voltage across it provides the feedback to regulate the LED current. The current regulation amplifier then compares the actual LED current to the programmed LED current and adjusts VC as necessary. The voltage regulation amplifier overrides the current regulation amplifier, when the FB pin voltage approaches an internal 1V reference. An external resistor network from the LED string to the FB pin provides an indication of the LED string voltage and allows the voltage amplifier to prevent overvoltage of the LED string. The FB voltage is also monitored to detect fault conditions like open and short-circuits, which are then reported by pulling the FAULT pin low. The response to a fault can be selected either to try hiccup restarts or to latch-off by the choice of an external resistor connected to the SS pin. Refer to Applications Information for a detailed explanation of fault responses. Finally, pulse-width-modulation (PWM) of the LED current is achieved by turning on and off an external PMOS switch between the inductor and the string of LEDs. An external pulse at the PWM pin controls the state of the PWM driver, or a DC voltage at the PWM pin dictates the duty ratio of an internal PWM pulse, whose frequency is programmed by an external resistor at the RP pin. After each pulse, when the PMOS switch is open, the LT3932 preserves the voltages of the capacitors at VC and VOUT to ensure a rapid recovery for the next pulse. Rev B For more information www.analog.com 13 LT3932/LT3932-1 APPLICATIONS INFORMATION The following is a guide to selecting the external components and configuring the LT3932 according to the requirements of an application. Programming LED Current with the CTRL Pin The primary function of the LT3932 is to regulate the current for a string of LEDs. This current should pass through a series current sense resistor that can be placed anywhere in the string. Then the voltage across this resistor will be sensed by the current regulation amplifier through the ISP and ISN pins and regulated to a level programmed by the CTRL pin. The maximum resistor voltage that can be programmed is 100mV, which corresponds to 2A through the LED string when a 50m current sense resistor is used. Additionally, the LT3932 is capable of interpreting a pulse at the CTRL pin. The high level of the pulse must be greater than 1.6V. The low level must be less than 400mV. The frequency must be greater than 100kHz and less than 1MHz. Then the regulated voltage between ISP and ISN will vary with the duty ratio of the pulse as shown in Figure 2. In this case, the LED current is zero for duty ratios less than 12.5% and reaches its maximum above 62.5%. The LT3932 will cease switching if the duty ratio of the CTRL pin pulse is less than 10%, and also for DC CTRL pin voltages less than 200mV. ILED 100mV RSNS To allow for this maximum current, the CTRL pin may be connected directly to the VREF pin, which provides an accurate 2V reference. Lower current levels can be DCTRL < 10% CTRL-OFF 50mV RSNS ILED 100mV RSNS VCTRL < 200mV CTRL-OFF 0 12.5% 37.5% 62.5% 75% DCTRL 3932 F02 50mV RSNS Figure 2. Duty Ratio CTRL Range 0 0.25V 0.75V 1.25V 1.5V VCTRL 3932 F01 To reduce the LED current when the temperature of the LEDs rises, use resistors with negative temperature coefficient (NTC) in the network from VREF to CTRL as shown in Figure 3. Figure 1. Analog CTRL Range programmed by DC CTRL voltages between 250mV and 1.25V as shown in Figure 1. Below 250mV, the CTRL pin commands zero LED current, and above 1.25V, it commands the maximum. When an independent voltage source is not available, the intermediate CTRL voltages may be derived from the 2V reference at the VREF pin using a resistor network or potentiometer as long as the total current drawn from the VREF pin is less than 1mA. 14 VREF VREF RCTRL1 LT3932 RCTRL1 RNTC RCTRL2 LT3932 CTRL CTRL RCTRL2 3932 F03 RNTC Figure 3. Setting CTRL with NTC Resistors Rev B For more information www.analog.com LT3932/LT3932-1 APPLICATIONS INFORMATION 100 Setting Switching Frequency with the RT Pin 80 60 AMPLITUDE (dBuV) The switching frequency of the LT3932 is programmed by a resistor connected between the RT pin and GND. Values of the RT resistor from 45.3k up to 523k program frequencies from 2MHz down to 200kHz as shown in Table 1. Higher frequencies allow for smaller external components but increase switching power losses and radiated EMI. 40 20 0 -20 Table 1. RT Resistance Range SWITCHING FREQUENCY RT 2.0MHz 45.3k 1.6MHz 59.0k 1.2MHz 80.6k 1.0MHz 97.6k 750kHz 133k 500kHz 205k 400kHz 255k 300kHz 348k 200kHz 523k -40 WITH SSFM WITHOUT SSFM 1 3 5 7 FREQUENCY (MHz) 9 11 3932 F04 Figure 4. Typical Average Conducted Emissions The attenuation varies depending on the chosen switching frequency, the range of frequencies in which interference is measured, and whether a test measures peak, quasipeak, or average emissions. The results of several other such emission measurements are with select Typical Applications. Synchronizing Switching Frequency Understanding the Current Limit The switching frequency can also be synchronized to an external clock connected to the SYNC/SPRD pin. The high level of the external clock must be at least 1.4V, and the frequency must be between 200kHz and 2MHz. The RT resistor is still required in this case, and the resistance should correspond to the frequency of the external clock. If the external clock ever stops, the LT3932 will rely on the RT resistor to set the frequency. The choice of switching frequency should be made knowing that, although the maximum LED current that can be programmed with the CTRL pin is 2A, the inductor current may exceed 2A when the frequency is high and the output voltage is low as in a short-circuit. This is because there is a minimum on-time for which the SW pin will be driven high during each switching period. The inductor current increases during this time, and if the frequency is high and the output voltage low, there may not be enough off-time remaining in each switching period for the inductor current to decrease back to the level at which it started. In this case, the net inductor current would increase with each switching period regardless of the state of the CTRL pin. Enabling Spread Spectrum Frequency Modulation Connecting SYNC/SPRD to INTVCC will enable spread spectrum frequency modulation (SSFM). The switching frequency will vary from the frequency set by the RT resistor to 125% of that frequency. If neither synchronization nor SSFM is required, connect SYNC/SPRD to GND. As shown in Figure 4, enabling SSFM can significantly attenuate the electromagnetic interference that the LT3932, like all switching regulators, emits at the switching frequency and its harmonics. This feature is designed to help devices that include the LT3932 perform better in the various standard industrial tests related to interference. To prevent large inductor currents that would damage the LT3932, the high-side switch is not turned on until the inductor current decreases to less than the DA current limit, which is approximately 2.3A. While the high-side switch is off, the current is sensed through the low-side switch. The peak inductor current may increase to 3.6A, but the off-time and the switching period are extended until the inductor current reaches equilibrium as shown in Figure 5. Rev B For more information www.analog.com 15 LT3932/LT3932-1 APPLICATIONS INFORMATION Selecting an Output Capacitor DA CURRENT LIMIT OUTPUT SHORTED INDUCTOR CURRENT 500mA/DIV 100s/DIV 3932 F05 Figure 5. Extended Off-Time at Current Limit The DA current limit is relevant only when the output capacitor is shorted to GND. When instead the LED string is shorted to GND, the voltage across the external PMOS (described later) is high enough that the required on-time is greater than the minimum on-time. This means that, in spite of a shorted LED string, the inductor current remains in regulation even at the highest switching frequency. The inductor must be rated for the current limit regardless of the intended application. Its value, in most applications, should be selected such that the inductor current ripple is not more than 25% of the maximum output current. When that current is 2A, for example, the minimum inductance can be calculated using the following equation: VOUT VIN(MAX) * VIN(MAX) - VOUT 1MHz * fSW 1V However, for high output voltages even the above equation would suggest an inductance value that is too small. For stability, the LT3932 requires an inductance greater than: L = 1H * VOUT 1MHz * 1V fSW Choose the larger of the values given by these equations. The manufacturers featured in Table 2 are recommended sources of inductors. Table 2. Inductor Manufacturers MANUFACTURER WEBSITE Wurth Elektronik www.we-online.com Coilcraft www.coilcraft.com 16 COUT = 100F * 1V 1MHz * VOUT fSW However, applications may still be stable with more or less capacitance, and more capacitance may improve LED current waveforms for large PWM dimming ratios. Use X7R or X5R ceramic capacitors as they retain their capacitance better than other capacitor types over a wide voltage and temperature range. Sources of quality ceramic and electrolytic capacitors are listed in Table 3. Table 3. Capacitor Manufacturers Selecting an Inductor L = 2H * Some applications are sensitive to ripple current in the LED string. In those cases, a capacitor at the output will absorb part of the inductor current ripple and thereby reduce the LED current ripple. Typically, the value of this capacitance is inversely proportional to the switching frequency and the output voltage as shown below: MANUFACTURER WEBSITE Murata Manufacturing www.murata.com Garrett Electronics www.garrettelec.com AVX www.avx.com Nippon Chemi-Con www.chemi-con.co.jp/e Stabilizing the Regulation Loop Stabilizing the regulation loop typically requires only a capacitor CC connected from the VC pin to GND. For most designs, values between 1nF and 10nF are suitable. When using an output capacitor COUT larger than 10F, as is needed for large PWM dimming ratios, a resistor RC in series with CC may be necessary. Larger values of COUT require larger values of RC. See Typical Applications for some examples. Selecting and Placing the Input Capacitors Although they do not impact stability, several capacitors are necessary between VIN and GND to properly bypass the input supply voltage. At least 10F is required in total, although it does not have to be composed entirely of ceramic capacitors placed very close to the VIN pins. However, it is important that a ceramic capacitor be placed Rev B For more information www.analog.com LT3932/LT3932-1 APPLICATIONS INFORMATION as close as possible to each of the pairs of VIN pins (Pins 16 and 17 as well as 20 and 21) and their adjacent GND pins as shown in Figure 6. These two capacitors should be at least 1F if possible. Because the SW pins lie between the VIN pins, it is convenient to join the VIN pins using a trace on the second layer of the circuit board. Another 1F capacitor should be placed very close to the remaining VIN pin (Pin 26), which supplies the internal control circuitry. 8 7 6 5 4 3 2 1 9 28 10 27 11 26 29 12 GND VIN 25 13 24 14 23 15 16 17 18 19 20 21 22 1F CERAMIC GND 1F VIN VIN GND 1F CERAMIC GND 100nF BST SW TOP LAYER 3932 F06 BOTTOM LAYER Figure 6. Placement of Input Capacitors Selecting a MOSFET for PWM Dimming Pulse-Width-Modulation (PWM) dimming of the LED current is an effective way to control the brightness of the light without varying its color. The brightness can also be adjusted more accurately this way than by varying the current level. The LT3932 features a PWMTG driver that is intended for a high-voltage PMOS switch in position to effectively PWM dim a string of LEDs from the output capacitor and current sense resistor. When the switch is open and the string is disconnected, the LED current will be zero. In contrast to a low-side NMOS driver, this feature eliminates the need for a dedicated return path for the LED current in automotive applications or other grounded chassis systems. The gate driver for this PMOS draws power through the VOUT pin, which must be connected even in applications that do not require PWM dimming. When the PWM pin voltage is greater than 1.4V, the driver will pull the gate of the PMOS to a maximum of 10V below the VOUT pin. If VOUT is below 10V, the gate drive is necessarily reduced. For constant current applications, leave PWMTG open, connect the load directly after the current sense resistor, and connect PWM to INTVCC. In these cases, analog dimming may be implemented with the CTRL pin. The drain-source voltage rating of the chosen PMOS should be greater than the maximum output voltage. Typically the output voltage is a little higher than the sum of the forward voltages of the LEDs in the string. However, when the string is broken, the output voltage will begin to increase due to the imbalance of inductor current and load current. As described in detail later, the LT3932 will not reduce the inductor current nor limit the output voltage until the FB pin voltage approaches 1V. Therefore, the maximum output voltage is ultimately determined by the resistor network between FB and VOUT. In most applications, the gate-source voltage rating of the PMOS should be at least 10V. The only exceptions to this rule are applications for which the output voltage is always less than 10V. The PWMTG driver will try to pull the gate of the PMOS down to 10V below VOUT, but it cannot pull the gate below GND. Therefore, when the maximum output voltage is less than 10V, the PMOS gate source voltage rating will be sufficient if it is merely equal to or greater than the output voltage. Finally, the drain current rating of the PMOS must exceed the programmed LED current. Assuming this condition and the conditions above are met, the only electrical parameter to be considered is the on-resistance. Other parameters such as gate charge are less important because PWM dimming frequencies are typically too low for efficiency to be affected noticeably by gate charging loss or transition loss. Rev B For more information www.analog.com 17 LT3932/LT3932-1 APPLICATIONS INFORMATION Table 4 lists recommended manufacturers of PMOS devices. Table 4. PMOS Manufacturers MANUFACTURER WEBSITE Infineon www.infineon.com Vishay Intertechnology www.vishay.com NXP Semiconductors www.nxp.com Selecting an RP Resistor for Internal PWM Dimming If the RP pin is tied to GND, an external pulse-width modulated signal at the PWM pin will control PWM dimming of the LED load. The signal will enable the PWMTG driver and turn on the external PMOS device when it is higher than 1.4V. However, the LT3932 is capable of PWM dimming even when an external PWM signal is not available. In this case, an internal PWM signal with frequency set by a resistor at the RP pin and duty ratio set by a DC voltage at the PWM pin will control the PWMTG driver. The RP resistor should be one of the seven values listed in Table 5. For each of these values, the PWM frequency is a unique ratio of the switching frequency. Table 5. Internal PWM Dimming Frequencies RP 28.7k 47.5k 76.8k 118k 169k 237k 332k 2MHz 7.81kHz 3.91kHz 1.95kHz 977Hz 488Hz 244Hz 122Hz SWITCHING FREQUENCY 1MHz 500KHz 3.91kHz 1.95kHz 1.95kHz 977Hz 977Hz 488Hz 488Hz 244Hz 244Hz 122Hz 122Hz 61Hz 61Hz 31Hz 250KHz 977Hz 488Hz 244Hz 122Hz 61Hz 31Hz 15Hz When using the internal PWM signal, set the voltage at the PWM pin between 1V and 2V. The PWMTG driver will stay off if PWM is below 1V, and it will stay on if PWM is above 2V. Between 1V and 2V there are 128 evenly spaced thresholds corresponding to 128 discrete PWM duty ratios from 0% to 100%. This range of 1V to 2V has been chosen so that the PWM voltage may be set using a potentiometer or a resistor network and the 2V reference available at the VREF pin. Place a small 1F ceramic capacitor near the PWM pin to ground. 18 There are a couple of exceptions to the PWM dimming behavior described above. First, once initiated, the PWM on-time will will last at least four switching cycles regardless of the signal at the PWM pin and the resistor at the RP pin. This ensures that the current regulation loop has enough time to reach equilibrium but still allows for a 5000:1 dimming ratio when the PWM frequency is 100Hz and the switching frequency is 2MHz. The LT3932-1 does not enforce this four-cycle limit so that dimming ratios of 10000:1 or greater are possible in some applications. Second, to avoid excessive start-up times, after the first PWM pulse, PWMTG will stay on until the SS pin voltage reaches 1.7V or the LED current has reached 10% of the full-scale current. PWM Dimming with Very Long Off Times To enhance PWM dimming, the VOUT and VC pin voltages are driven when the PWM pulse (internal or external) is at a logic low to maintain the charge on the capacitors at those pins. Consequently, when PWM returns to a logic high state, the LED current can quickly reach the regulated level even if PWM was low for a very long time. This feature facilitates machine vision applications which require a synchronized strobe light or brief illuminating flashes on short delay. Monitoring LED Current The ISMON pin provides an amplified and buffered monitor of the voltage between the ISP and ISN pins. The gain of the internal amplifier is ten, and the speed is fast enough to track the pulse-width modulated LED current. However, as shown in Figure 7, the ISMON voltage can be filtered with a resistor-capacitor network to monitor the average LED current instead. LT3932 ISMON RMON CMON 3932 F07 Figure 7. ISMON Filter Configuration Rev B For more information www.analog.com LT3932/LT3932-1 APPLICATIONS INFORMATION The resistor should be 1M. The capacitance can be as large or small as needed without affecting the stability of the internal amplifier. For example, when the PWM frequency is 200Hz, a 100nF capacitor combined with the 1M resistor would limit the ripple on ISMON to 1%. VOUT LT3932 RFB2 FB RFB1 R VOUT(MAX) = 1V * 1+ FB2 RFB1 3932 F08 Figure 8. FB Resistor Configuration Selecting the FB Resistors Two resistors should be selected to form a network between the output voltage and the FB pin as shown in Figure 8. This network forms part of a voltage regulation loop when FB is nearly 1V. In this case, the LT3932 will override the programmed LED current to lower the output voltage and limit FB to 1V. This resistor configuration therefore determines the maximum output voltage. Note that this voltage limit may be reached inadvertently if it is set too close to the typical output voltage and the output capacitor is too small. To avoid interference with the current regulation, the feedback resistors should be chosen such that FB is about 700mV when the LEDs are conducting. For a 12V string of LEDs, design for a maximum output voltage of about 17V. Start with a 10k resistor for RFB1. To calculate the value of RFB2, add 10k for every volt of difference between FB (1V) and the maximum output voltage. In this case, the nearest standard 1% value for RFB2 would be 162k. In this way, the LT3932 can also be configured as a voltage regulator instead of an LED driver. It will regulate the output voltage near the programmed maximum as long as the load current is less than the current level programmed by CTRL. Understanding FB Overvoltage Lockout It is possible that the FB voltage can exceed the 1V limit. If the output voltage is near the maximum when the LED string opens, it may take too long for the feedback loop to adjust the inductor current and avoid overcharging the output. However, if the FB voltage exceeds the 1.05V Overvoltage Lockout Threshold, the LT3932 will immediately stop switching and resume only when FB decreases to 1V. This threshold may be routinely exceeded when the LT3932 is being operated as a voltage regulator and the load current decreases rapidly. In this case, the pause in switching limits the output overshoot and ensures that the voltage is back in regulation as quickly as possible. For safe operation, choose RFB2 and RFB1 values to ensure the output voltage is not greater than VIN when the FB voltage is 1.05V. Open and Shorted LED Fault Detection and Response The resistor network formed by RFB1 and RFB2 also defines the criteria for two fault conditions with respect to the LED string: short and open-circuits. For the LT3932, a shortcircuit is when FB is less than 200mV. An open-circuit is when FB is greater than 950mV and simultaneously the difference between ISP and ISN is less than 10mV (the C/10 threshold). The latter condition ensures that the output current is low (as it should be in an open-circuit) not just that output voltage is high as it may be when the LEDs are conducting a large current. In both cases, a fault is indicated by an internal device pulling the voltage at the FAULT pin low. There is nothing internal that pulls this voltage high, so an external resistor between INTVCC and FAULT is necessary as shown in Figure 9. This configuration allows multiple FAULT pins and similar pins on other parts to be connected and share a single resistor. INTVCC RFAULT LT3932 FAULT 3932 F09 Figure 9. FAULT Resistor Configuration Rev B For more information www.analog.com 19 LT3932/LT3932-1 APPLICATIONS INFORMATION Soft-Start and Fault Modes The SS pin has two functions. First, it allows the user to program the output voltage startup ramp rate. An internal 20A current pulls up the SS pin to INTVCC. Connecting an external capacitor CSS from the SS pin to GND, as shown in Figure 10, will generate a linear ramp voltage. The LT3932 regulates the FB pin voltage to track the SS pin voltage until VOUT is high enough to drive the LED at the commanded current level. INTVCC RSS LT3932 SS CSS 3932 F10 Figure 10. SS Capacitor and Resistor Configuration The SS pin is also used as a fault timer. After a fault is detected, an internal 1.25A current sink will begin to discharge the soft-start capacitor and lower the voltage at the SS pin. When the voltage falls from 3.3V to 1.7V, all switching will cease, but the SS pin will continue to discharge. Switching will not resume until SS reaches 200mV. At this point, the 20A current will recharge the soft-start capacitor, and the LT3932 will try to switch again. If the fault persists when SS returns to 1.7V, the process will repeat as shown in Figure 11. The charging rate of the soft-start capacitor is much faster than the discharging rate, so while the fault persists, the LT3932 will only attempt switching for a relatively short part of the cycle before being interrupted. Although the LT3932 can safely endure a short-circuit while continuously switching, this hiccup action saves power. The frequency of the hiccups is inversely proportional to CSS and 100nF yields about 8Hz. The operating point of a voltage regulator supplying light loads will frequently satisfy the criteria for an open-circuit, and the hiccup behavior would therefore be very disruptive. So when the LT3932 is configured as a voltage regulator, a resistor RSS should be connected between INTVCC and SS as shown in Figure 10. The current that pulls down the SS pin during a fault is so weak that if RSS is 1M, the voltage at the SS pin will never reach 1.7V. Therefore, the LT3932 will not stop switching or start to hiccup. With this resistor, the LT3932 will continue switching and rely on overvoltage and overcurrent protection to guarantee safe operation in the event of open-circuits and short-circuits. If the resistor is changed to 2M, then the SS pin may be discharged to less than 1.7V, but not less than 200mV as shown in Figure 12. The LT3932 will consequently cease switching permanently until being reset by the EN/UVLO pin or by powering off. Some applications may demand this behavior so that short and open-circuits can be investigated manually before resuming normal operation. This latch-off behavior is the third of three ways that the LT3932 can be programmed to respond to faults--the other two being continuous operation and the default hiccup behavior. FAULT DETECTED FAULT DETECTED CONTINUOUS RSS = 1MEG SS 1V/DIV SS 1V/DIV FAULT CLEARED 10ms/DIV 3932 F11 Figure 11. Hiccup Response to Fault 20 LATCH-OFF RSS = 2MEG 10ms/DIV 3932 F12 Figure 12. Latch-Off Response to a Fault Rev B For more information www.analog.com LT3932/LT3932-1 APPLICATIONS INFORMATION Dimming with External Drivers Continuous operation in response to a fault also enables the LT3932 to operate with external switches that shunt some or all of the LEDs in the string. The LT3965 8-switch Matrix LED Dimmer, for example, is designed to shunt a changing combination of up to eight LEDs in a single string with independent PWM dimming signals. See Typical Applications for more details. Programming the EN/UVLO Threshold An external voltage source can be used to set the voltage at the EN/UVLO pin to enable or disable the LT3932. The LT3932 will stop switching, disable the PWMTG driver, and reset the SS pin when the voltage at EN/UVLO drops below 1.15V, but internal circuitry will continue drawing current. Full shutdown is guaranteed when EN/UVLO is below 300mV, and in full shutdown the LT3932 will draw less than 2A. For applications in which the level of the source driving EN/UVLO changes slowly, 20mV of hysteresis has been added to the 1.15V enable threshold. Alternatively, a resistor network can be placed between VIN and EN/UVLO as shown in Figure 13. In this case, EN/UVLO automatically falls below 1.15V and disables VIN REN2 LT3932 EN/UVLO REN1 3932 F13 Figure 13. EN/UVLO Resistor Configuration switching when VIN falls below a certain level, called the Undervoltage Lockout (UVLO) threshold, which is defined by resistors REN1 and REN2. Additionally, a 4A current is designed to flow into EN/UVLO when the pin voltage is below the threshold. This current provides additional hysteresis. To define the hysteresis (VHYST) and the UVLO threshold (VUVLO) select REN1 and REN2 according to the following equations: REN2 = VHYST VUVLO - 4A 480A REN1 = 1.15 * REN2 VUVLO - 1.15 For example, to program a 10V threshold with 1V of hysteresis, use 226k and 29.4k for REN2 and REN1, respectively. Planning for Thermal Shutdown The LT3932 automatically stops switching when the internal temperature is too high. The temperature limit is guaranteed to be higher than the operational temperature of the part. During thermal shutdown, all switching is terminated, SS is forced low, and the LEDs are disconnected using the PWMTG driver. The exposed pad on the bottom of the package must be soldered to a ground plane. Vias placed directly under the package are necessary to dissipate heat. Following these guidelines, the official four-layer demo board DC2286A reduces thermal resistance JA to 25C/W, but with a compromised board design JA could be 40C/W or higher. Rev B For more information www.analog.com 21 LT3932/LT3932-1 APPLICATIONS INFORMATION Designing the Printed Circuit Board Note that large switched currents flow through the local input capacitors and the VIN and GND pins. The loops traveled by these currents should be made as small as possible by keeping the capacitors as close as possible to these pins. These capacitors, as well as the inductor, should be placed on the same side of the board as the LT3932 and connected on the same layer. Other large, bulk input capacitors can be safely placed farther from the chip and on the other side of the board. Create a Kelvin ground network by keeping the ground connection for all of the other components separate. It should only join the ground for the input and output capacitors and the return path for the LED current at the exposed pad. 22 There are a few other aspects of the board design that improve performance. An unbroken ground plane on the second layer dissipates heat, but also reduces noise. Likewise minimizing the area of the SW and BST nodes reduces noise. The traces for FB and VC should be kept short to lessen the susceptibility to noise of these high impedance nodes. Matched kelvin connections from the external current sense resistor RS to the ISP and ISN pins are essential for current regulation accuracy. The 2.2F INTVCC and VREF capacitors as well as the 22nF BST capacitor should be placed as closely as possible to their respective pins. A capacitor for the CTRL pin and, when the internal dimming feature is used, the PWM pin, can compensate for compromised layouts. Finally, a diode with anode connected to ground and cathode to the drain of the PWMTG MOSFET can protect that device from overvoltage caused by excessive inductance in the LED string. Please refer to the demo board layout of the LT3932 for an example of how to implement these recommendations. Rev B For more information www.analog.com LT3932/LT3932-1 TYPICAL APPLICATIONS 2A LED Driver with Duty Cycle LED Current D1 INTVCC VIN 36V VIN ENABLE CIN1 10F EN/UVLO CREF 2.2F RFAULT 100k FAULT CBST 22nF L1 150H SW CIN2 2x1F 3.3V 0V 3.3V 0V CVCC 2.2F BST VOUT CTRL LT3932 FB PWM VREF GND RFB2 287k RFB1 10k COUT 2x10F L1: WURTH 7447709151 M1: VISHAY Si4447ADY RS: OHMITE LVK12R050D COUT1: MURATA GRM32ER71H106K D1: NEXPERIA BAT46WJ 2A MAX ISP RS 50m INTVCC ISN FAULT PWMTG SYNC/SPRD SS CSS 100nF ISMON RT RP RT 523k 200kHz M1 ISMON LED1 VC CC 10nF LED8 3932 TA02 Digital CTRL 50%, Digital PWM 100% Digital CTRL 25%, Digital PWM 100% CTRL 5V/DIV CTRL 5V/DIV PWM 2V/DIV PWM 2V/DIV LED CURRENT 1A/DIV LED CURRENT 1A/DIV 500ns/DIV 3932 TA02a 500ns/DIV Digital CTRL 25%, Digital PWM 50% Digital CTRL 25%, Digital PWM 25% CTRL 5V/DIV CTRL 5V/DIV PWM 5V/DIV PWM 5V/DIV LED CURRENT 500mA/DIV LED CURRENT 500mA/DIV 5ms/DIV 3932 TA02b 3932 G33 5ms/DIV 3932 TA02d Rev B For more information www.analog.com 23 LT3932/LT3932-1 TYPICAL APPLICATIONS 24V Voltage Regulator with Spread Spectrum D1 INTVCC VIN 29V TO 36V CIN1 10F CIN2 2x1F VIN REN2 576k BST SW EN/UVLO REN1 23.7k VOUT LT3932 FB ISP SYNC/SPRD RSS 1MEG RFAULT 100k CSS 10nF PWMTG NOT USED ISMON RT RP VC RC 20k CC 10nF RT 45.3k 2MHz L1: COILCRAFT XAL5050-153 RS: OHMITE LVK12R050D COUT: GRM32ER71H106K D1: NEXPERIA BAT46WJ 3932 TA03 Efficiency 95 2.0 94 1.5 93 1.0 500 1000 1500 OUTPUT CURRENT (mA) VOUT 1V/DIV 2.5 ON-CHIP LOSS (W) EFFICIENCY (%) Load Step Response (100mA to 1A) 3.0 EFFICIENCY (29VIN) LOSS (29VIN) EFFICIENCY (36VIN) LOSS (36VIN) 0 COUT 2 x 10F VOUT 24V, 2A MAX FAULT SS L1 15H RS 50m ISN INTVCC CVCC 2.2F 92 RFB2 10k GND CTRL PWM 96 RFB1 226k VREF CREF 2.2F 97 CBST 22nF ILOAD 500mA/DIV 100s/DIV 3932 TA03b 0.5 2000 3932 TA03a 24 Rev B For more information www.analog.com LT3932/LT3932-1 TYPICAL APPLICATIONS D1 INTVCC VIN 8V TO 36V FB1 VIN CIN1 2x100nF 50V 0402 CIN2 4.7F 50V 1206 CIN3 33F 50V ELYT. CIN4 1F 50V 0603 CIN5 2x470nF 50V 0402 CREF 2.2F BST CBST 22nF REN2 232k REN1 39.2k L1 2.2H SW EN/UVLO VOUT LT3932 VREF RFB2 69.8k FB CTRL PWM RFB1 10k GND COUT 4.7F 16V 0805 1A MAX ISP RS 100m ISN RS: SUSUMU KRL1220D-M-R100-F D1: NXP PMEG4010CEJ FB1,2: WURTH 742792040 L1: WURTH 74438323022 M1: VISHAY Si2399DS D1: NEXPERIA BAT46WJ INTVCC CVCC 10F PWMTG FB2 SS RT RP VC RC 24.9k CC 150pF RT 45.3k 2MHz CSS 1nF ISMON, FAULT NOT USED M1 SYNC/SPRD CB2 100nF 16V 0402 LED1 D1 LED2 3932 TA07 CISPR25 Peak Radiated Emissions Test 80 70 70 60 60 AMPLITUDE (dBV/m) AMPLITUDE (dBV) CISPR25 Peak Conducted Emissions Test 80 50 40 30 20 10 0 -10 -20 0.1 10 FREQUENCY (MHz) DC2286A DEMO BOARD 14V INPUT TO 6V OUTPUT AT 1A 50 40 30 20 10 0 CLASS 5 PEAK LIMIT MEASURED EMISSIONS AMBIENT NOISE 1 CLASS 5 PEAK LIMIT MEASURED EMISSIONS AMBIENT NOISE -10 100 -20 200 0 60 50 40 30 20 10 DC2286A DEMO BOARD 14V INPUT TO 6V OUTPUT AT 1A 1000 3932 TA07b 20 10 0 100 900 30 -10 10 FREQUENCY (MHz) 800 40 -10 1 700 50 0 -20 0.1 400 500 600 FREQUENCY (MHz) CLASS 5 AVERAGE LIMIT MEASURED EMISSIONS AMBIENT NOISE 70 AMPLITUDE (dBV/m) AMPLITUDE (dBV) 60 300 CISPR25 Average Radiated Emissions Test 80 CLASS 5 AVERAGE LIMIT MEASURED EMISSIONS AMBIENT NOISE 70 200 DC2286A DEMO BOARD 14V INPUT TO 6V OUTPUT AT 1A 3932 TA07a CISPR25 Average Conducted Emissions Test 80 100 200 3932 TA07c -20 0 100 200 300 400 500 600 FREQUENCY (MHz) DC2286A DEMO BOARD 14V INPUT TO 6V OUTPUT AT 1A 700 800 900 1000 3932 TA07d Rev B For more information www.analog.com 25 LT3932/LT3932-1 TYPICAL APPLICATIONS 2A LED Driver with Internal PWM Dimming D1 INTVCC VIN 12V TO 24V VIN BST REN2 274k CIN2 2x1F REN1 29.4k RFB2 110k LT3932 COUT 100F FB CREF 2.2F RFB1 10k CTRL RREF2 100k PWM ISP RS 50m ISN RFAULT 100k FAULT 2A MAX GND INTVCC CVCC 2.2F L1: WURTH 74404064082 M1: INFINEON IRF7204 RS: OHMITE LVK12R050D COUT: AVX TPME107M020R0035 D1: NEXPERIA BAT46WJ VOUT VREF RREF1 100k L1 8.2H SW EN/UVLO CIN1 10F CBST 22nF PWMTG FAULT ISMON M1 ISMON LED1 SYNC/SPRD SS CSS 100nF RT RP RT 45.3k 2MHz VC RP 28.7k 7.8kHz LED2 RC 162k LED3 CC 10nF 3932 TA06 Internal PWM Dimming SW 20V/DIV SW 20V/DIV PWMTG 10V/DIV PWMTG 10V/DIV IL 1A/DIV IL 1A/DIV ILED 1A/DIV ILED 1A/DIV PWM = 1.078V 26 Internal PWM Dimming 2s/DIV 3932 TA06a PWM = 1.132V 2s/DIV 3932 TA06b Rev B For more information www.analog.com LT3932/LT3932-1 TYPICAL APPLICATIONS Multiple String Drivers from Single Boosted 36V Input VBUCK 36V, 5A MAX L0 4.2H D0 M0 VIN GATE SHDN/UVLO SENSE R0 4m SYNC RSHDN1 12.1k LT3757 GND RFB1 348k COUT 35F 50V + VIN 6V MIN FOR OPERATION 10V MIN FOR FULL CURRENT CIN 10F RSHDN2 48.7k RT FBX COUT 5F RFB2 16.2k L0: WURTH 7443630420 M0: INFINEON BSZ040N04LS R0: VISHAY WSLP25124L000F D0: ONSEMI MBR1240MFS INTVCC SS VC RC 10k CC 10nF CVCC 4.7F CSS 100nF RT 30.9k 400MHz +2 LT3932 (1A EACH) D2 D1 INTVCC INTVCC CIN1 10F VIN CIN2 2x1F BST SW ENABLE1 3.3V 0V CREF 2.2F EN/UVLO PWM RCTRL2 49.9k RCTRL1 30.1k 3.3V 0V VOUT LT3932 VREF CTRL FB GND CSS 100nF CIN2 2x1F CIN1 10F RFB1 110k RFB2 10k VIN BST SW ENABLE2 3.3V 0V COUT 4.7F EN/UVLO VOUT LT3932 PWM 1A MAX GND CTRL PWMTG ISMON RT RP VC RT 45.3k 2MHz L1: WURTH 74437336100 M1: INFINEON IRF7204 RS1: OHMITE LVK12R050D COUT: MURATA GRM32ER714475K D1: NEXPERIA BAT46WJ RFB1 287k RFB2 10k L2 15H COUT 4.7F 1A MAX M1 RS2 100m SYNC/SPRD RFAULT 100k CSS 100nF ISN INTVCC PWMTG RT M2 ISMON FAULT SS CVCC 2.2F CC 10nF CBST 22nF ISP 3.3V 0V ISN FAULT FB VREF CREF 2.2F RS1 50m INTVCC SS CVCC 2.2F L1 10H ISP SYNC/SPRD RFAULT 100k CBST 22nF RP VC RT 45.3k 2MHz L2: COILCRAFT LPS8045B-153 M2: VISHAY Si2319CDS RS2: OHMITE LVK12R100D COUT: MURATA GRM32ER71H475K D2: NEXPERIA BAT46WJ 8x LED CC 10nF 3932 TA05 Rev B For more information www.analog.com 27 LT3932/LT3932-1 PACKAGE DESCRIPTION UFD Package 28-Lead Plastic QFN (4mm x 5mm) (Reference LTC DWG # 05-08-1712 Rev C) 0.70 0.05 4.50 0.05 3.10 0.05 2.50 REF 2.65 0.05 3.65 0.05 PACKAGE OUTLINE 0.25 0.05 0.50 BSC 3.50 REF 4.10 0.05 5.50 0.05 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 4.00 0.10 (2 SIDES) R = 0.05 TYP 0.75 0.05 PIN 1 NOTCH R = 0.20 OR 0.35 x 45 CHAMFER 2.50 REF R = 0.115 TYP 27 28 0.40 0.10 PIN 1 TOP MARK (NOTE 6) 1 2 5.00 0.10 (2 SIDES) 3.50 REF 3.65 0.10 2.65 0.10 (UFD28) QFN 0816 REV C 0.200 REF 0.00 - 0.05 0.25 0.05 0.50 BSC BOTTOM VIEW--EXPOSED PAD NOTE: 1. DRAWING PROPOSED TO BE MADE A JEDEC PACKAGE OUTLINE MO-220 VARIATION (WGHD-3). 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. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 28 Rev B For more information www.analog.com LT3932/LT3932-1 REVISION HISTORY REV DATE DESCRIPTION A 02/18 Added LT3932-1 to data sheet. 1 Added 10000:1 PWM dimming ratio for LT3932-1 with supporting text in Features and Description. 1 Added machine vision systems to Applications. 1, 22, 24, 25, 28 On Figure, added Schottky Diode from INTVCC to BST pin, changed boost capacitor from 100nF to 22nF. 1, 12, 22, 23, 24, 25, 26, 28 Changed JA from 43C/W to 25C/W (based on demo board measurement). 2 Sense voltage VCTRL changed from 2V to 1.5V. ISN pin current VISN value changed from 24V to 23.9V. 3 LED Current and LED Voltage Limit Graphs y-axis corrected to mV units. 7 DA Limit graph retitled to "DA Current Limit", input step changed from 20V upper limit to 25V on Input Voltage Transient Response graph. 9 Added additional BST pin description text; corrected BST capacitor value from 100nF to 22nF. 11 DA Current Limit added to Block Diagram. 12 Text added to describe DA Current Limit. 15 Added LT3932-1 text regarding four-cycle limit and machine vision usage. 18 Added text regarding JA equals 25C/W using DC2286 demo board, corrected boost capacitor value. 21 Corrected Typical Application figure, reduced VOUT from 30V to 24V, changed digital CTRL 50% graph y-axis from 5A/DIV to 5V/DIV. 22 Added Diode D1: Nexperia BAT46WJ. 07/18 1 Relabeled Soft-Start pin from S to SS. Add new Efficiency graph. B PAGE NUMBER Three revised UVLO graphs in Typical Performance Characteristics EN/UVLO description; Changed text from "A resistor network between this pin and GND" to ". . . this pin and VIN." VREF description; Changed buffered reference drive current from 2mA to 1mA Corrected RSS from 1m to 1M Changed Inductor L1 value from 7438323022 to 74438323022 Increased Inductor value from 8.2H to 10H Changed Inductor; New Product Number; Changed L1 From 7440463082 to 74437336100 23 22, 24, 25, 26, 28 5 10 10 24 25 27 27 Rev B Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license For is granted implication or otherwise under any patent or patent rights of Analog Devices. more by information www.analog.com 29 LT3932/LT3932-1 TYPICAL APPLICATION 700mA Matrix LED Driver with Individual Dimming for 6 LEDs D1 INTVCC VIN 32V VIN BST REN2 249k CIN1 10F 50V CIN2 2x1F 50V 0402 VOUT D7 RFB2 267k LT3932 VREF RFB1 10k RREF2 110k GND CTRL REN4 249k RDD 100k 700mA VIN EN/UVLO REN3 10.7k D8 D7 ISP RREF1 105k VDD COUT 22nF FB CREF 2.2F L1: WURTH 74437349330 D1-7: NXP PMEG4010CEJ RS: OHMITE LVK12R100DER D1: NEXPERIA BAT46WJ L1 33H SW EN/UVLO REN1 10.2k CBST 22nF S8 RS 100m S7 LT3965 ISN D6 D6 PWM START SYNC/SPRD SS RPWM 10k RSS 1M CSS 10nF VDD RSDA 10k S6 INTVCC CVCC 2.2F LED6 RT RP RT 287k 350kHz D2 VC D2 LED2 CC 330pF S2 D1 D1 LED1 S1 RSCL 10k RALERT 10k SDA SCL CVDD 2.2F ALERT PWMCLK 350kHz ADDR1-4 GND LEDREF 3.3V 0V PWMTG, FAULT, AND ISMON NOT USED 3932 TA04 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT3922 40V, 2A, 2MHz, Synchronous Boost LED Driver VIN: 2.7V to 40V, VOUT(MAX) = 40V, 5000:1 True Color PWMTM Dimming, 5mm x 5mm QFN and TSSOP-28E LT3965 8-Switch Matrix LED Dimmer VIN: 8V to 60V, Digital Programmable 256:1 PWM Dimming, I2C Multidrop Serial Interface TSSOP-28E Package LT3956 80V, 3.3A 1MHz, Step-Up/Down LED Driver VIN: 4.5V to 80V, VOUT(MAX) = 80V, 3000:1 True Color PWM Dimming, 5mm x 6mm QFN LT3474 36V, 1A, 2MHz, Step-Down LED Driver VIN: 4V to 36V, VOUT(MAX) = 13.5V, 400:1 True Color PWM Dimming, TSSOP-16E LT3475 Dual 36V, 1.5A, 2MHz, Step-Down LED Driver VIN: 4V to 36V, VOUT(MAX) = 13.5V, 3000:1 True Color PWM Dimming, TSSOP-20E LT3476 Quad 36V, 1.5A, 2MHz, Step-Up/Down LED Driver VIN: 2.8V to 16V, VOUT(MAX) = 36V, 1000:1 True Color PWM Dimming, 5mm x 7mm QFN LT3477 42V, 3A, 3.5MHz, Step-Up/Down LED Driver VIN: 2.5V to 25V, VOUT(MAX) = 40V, 4mm x 4mm QFN and TSSOP-20E LT3478 42V, 4.5A, 2.5MHz, Step-Up/Down LED Driver VIN: 2.5V to 26V, VOUT(MAX) = 42V, 3000:1 True Color PWM Dimming, TSSOP-16E LTM8040 36V, 1A, Module, Step-Down LED Driver VIN: 4V to 36V, VOUT(MAX) = 13V, 250:1 True Color PWM Dimming, 9mm x 15mm x 4.32mm LGA LTM8042 36V, 1A, Module, Step-Up/Down LED Driver VIN: 3V to 30V, VOUT(MAX) = 36V, 3000:1 True Color PWM Dimming, 9mm x 15mm x 2.82mm LGA LT3757 40V, 1MHz, Step-Up Controller VIN: 2.9V to 40V, Positive and Negative Output Voltages, 3mm x 3mm DFN and MSOP-10E 30 Rev B D16990-0-7/18(B) www.analog.com For more information www.analog.com ANALOG DEVICES, INC. 2018