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LT3763

3763fa

For more information www.linear.com/LT3763

PWM Dimming

PWM

10V/DIV

50V/DIV

5A/DIV

5µs/DIV

3763 TA01b

Typical applicaTion

FeaTures DescripTion

60V High Current

Step-Down LED Driver Controller

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 control

ler 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 protec

tion 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.

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.

20A, Pulse Width Modulated, Single LED Driver

applicaTions

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

High Power Architectural Lighting

Automotive Lighting

Aviation and Marine Strobe Lights

Solar-Powered Chargers, Laser Diodes

100µF

10V TO 30V

2.5mΩ

1k 1k

82.5k

EN/UVLO

FBIN

BOOST

REF

CTRL1

CTRL2

LT3763

GND

SENSE

–

INTV

220nF

1.5µH

22µF

2.5mΩ

FAULT

59k

4.7nF

47.5k

3763 TA01

12.1k

2.2µF

470k

PWMOUT

OUT

6V, 20A MAXIMUM

220µF

×2

PWM

SYNC

10nF

45.3k

84.5k

15.4k

33nF

10Ω 10Ω

47.5kΩ

1µF

50k

4.7µF

IVINNIVINP

IVINMON

ISMON

1nF

50Ω

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.

Summary of content (30 pages)

PAGE 1
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.
PAGE 2
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.............................................................
PAGE 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 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.
PAGE 4
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.
PAGE 5
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.
PAGE 6
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 13 TIMEOUT (µs) VFB (V) 1.51 1.49 10 20 30 40 IINTVCC (mA) 50 1.
PAGE 7
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.
PAGE 8
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 FAULT Hysteresis 25 50 75 100 125 150 TEMPERATURE (°C) Output Current Sense 75 2.0 1.5 0.8 0.4 50 VISMON (V) HYSTERESIS (mV) UPPER VFB (V) 0 3763 G30 1.2 0 0.
PAGE 9
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 ILOAD (A) 3763 G37 80 24 18 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
PAGE 10
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.
PAGE 11
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.
PAGE 12
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.
PAGE 13
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.
PAGE 14
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.
PAGE 15
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.
PAGE 16
LT3763 Applications Information PLOSS = ohmic loss + transition loss ⎛V ⎞ PLOSS ≈ ⎜ O •IO 2 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, 2 OHMIC 0 10 20 40 30 INPUT VOLTAGE (V) 3763 F04a Figure 4a. Power Loss Example for M1 2.5 2.0 1.
PAGE 17
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 CBOOST 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.
PAGE 18
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.
PAGE 19
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.
PAGE 20
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.
PAGE 21
LT3763 Applications Information VIN Average Current Mode Control Compensation VIN LT3763 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. R2 EN/UVLO R1 3763 F12 Figure 12.
PAGE 22
LT3763 Applications Information 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. 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.
PAGE 23
LT3763 Typical Applications 20A, Pulse Width Modulated, Single LED Driver RSENSE_IN 2.5mΩ VIN 10V TO 30V REN1 84.5k RFILTA 1k REN2 15.4k CFILT 1µF 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 VOUT 6V, 20A MAXIMUM COUT 220µF ×2 INTVCC RFAULT 47.5kΩ BG CTRL1 RS 2.
PAGE 24
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 24 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.
PAGE 25
LT3763 Typical Applications 3.3A, Six-Cell (36V) SLA Battery Charger RSENSE_IN 15mΩ VIN 48V RFILTA 1k CFILT 1µF IVINP ENABLE CREF 2.2µF RFILTB 1k IVINN CIN1 1µF VIN EN/UVLO TG VREF LT3763 CBOOST 220nF BOOST RS 15mΩ CVCC 22µF M2 RSA 10Ω GND PWMOUT ISMON PWM FB SS VC CSS 10nF 12V + RFB1 402k FAULT SYNC RT RSB 10Ω CS 33nF SENSE– IVINMON COUT 10µF + 12V SENSE+ FBIN VOUT 45V, 3.3A MAXIMUM 12V RFAULT 47.5kΩ BG RT 82.
PAGE 26
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 3763 TA05 Efficiency vs Load Current 100 VIN = 12V VOUT = 5V ILIMIT = 20A 95 EFFICIENCY (%) VOUT (V) RFB2 12.
PAGE 27
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– RT 200k RFAULT 100k CVCC 22µF M2 ×2 LUMINUS PT-121 CS 1nF RFB1 931k FAULT SYNC RT 400kHz 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.
PAGE 28
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.
PAGE 29
LT3763 Revision History REV DATE DESCRIPTION A 05/13 Clarified switching frequency resistor values PAGE NUMBER 3 Clarified offset voltage conditions 4 Clarified programming resistor value 4 Clarified end of 7th paragraph 13 Clarified CBOOST capacitor 17 Clarified programming resistor value and Figure 10 19 Clarified schematic 25, 27, 30 3763fa Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use.
PAGE 30
LT3763 Typical Application 70W, Solar Energy Harvester Compatible with Maximum Power Point Regulation PANEL VOLTAGE UP TO 60V 37V VIN REG POINT RSENSE_IN 10mΩ D1 RFILTA 1k D2 CFILT 1µF IVINP ENABLE Dn RFILTB 1k IVINN VIN EN/UVLO CREF 2.2µF RHOT 45.3k TG VREF LT3763 VREF INTVCC CTRL1 RFAULT 47.5kΩ COUT 50µF M2 RSA 10Ω RSB 10Ω CS 33nF SENSE– IVINMON PWMOUT ISMON PWM RFB1 121k FAULT SYNC RT RT 82.