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LT3517

3517fg

For more information www.linear.com/LT3517

FEATURES

APPLICATIONS

DESCRIPTION

Full-Featured LED Driver

with 1.5A Switch Current

The LT

3517 is a current mode DC/DC converter with an

internal 1.5A, 45V switch specifically designed to drive

LEDs. The LT3517 operates as a LED driver in boost,

buck mode and buck-boost mode. It combines a tradi-

tional voltage loop and a unique current loop to operate

as a constant-current source or constant-voltage source.

Programmable switching frequency allows optimization of

the external components for efficiency or component size.

The switching frequency of LT3517 can be synchronized

to an external clock signal. The LED current is externally

programmable with a 100mV sense resistor. The external

PWM input provides up to 5000:1 LED dimming. The CTRL

pin provides further 10:1 dimming ratio.

The LT3517 is available in the tiny footprint 16-lead QFN

(4mm × 4mm) and the 16-pin TSSOP packages. The

LT3517 provides a complete solution for both constant-

voltage and constant-current applications.

■

5000:1 True Color PWM

™

Dimming Ratio

■

1.5A, 45V Internal Switch

■

100mV High Side Current Sense

■

Open LED Protection

■

Adjustable Frequency: 250kHz to 2.5MHz

■

Wide Input Voltage Range:

Operation from 3V to 30V

Transient Protection to 40V

■

Operates in Boost, Buck Mode and Buck-Boost Mode

■

Gate Driver for PMOS LED Disconnect

■

Constant-Current and Constant-Voltage Regulation

■

CTRL Pin Provides 10:1 Analog Dimming

■

Low Shutdown Current: <1µA

■

Available in (4mm × 4mm) 16-Lead QFN and 16-Pin

TSSOP Packages

■

Display Backlighting

■

Automotive and Avionic Lighting

■

Illumination

■

Scanners

10µF

15µH

2.2µF

0.1µF

100mΩ

2.2µF

REF

ISP

TGEN GNDV

REF

16.9k

1MHz

3517 TA01a

0.1µF

SHDN

CTRL

PWM

SYNC

24V

3.3V

ISN

LT3517

PWM

1A Buck Mode LED Driver

Efficiency

PWM DUTY CYCLE (%)

EFFICIENCY (%)

100

20 40 60 80

3517 TA01b

100

CTRL = V

REF

L, LT, LTC, LTM, Burst Mode, 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, 7746300.

TYPICAL APPLICATION

Summary of content (20 pages)

PAGE 1
LT3517 Full-Featured LED Driver with 1.5A Switch Current FEATURES DESCRIPTION 5000:1 True Color PWM™ Dimming Ratio ■ 1.5A, 45V Internal Switch ■ 100mV High Side Current Sense ■ Open LED Protection ■ Adjustable Frequency: 250kHz to 2.
PAGE 2
LT3517 ABSOLUTE MAXIMUM RATINGS (Note 1) VIN, SHDN, PWM, TGEN (Note 3)..............................40V SW, ISP, ISN, TG.........................................................45V TG Pin Below ISP Pin.................................................10V FB, SYNC, SS, CTRL....................................................6V VC, RT, VREF.................................................................3V Operating Junction Temperature Range (Notes 2,4) LT3517E..............................................
PAGE 3
LT3517 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. (Note 2) VIN = 5V, SHDN = 5V, PWM = 5V unless otherwise noted.
PAGE 4
LT3517 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. (Note 2) VIN = 5V, SHDN = 5V, PWM = 5V unless otherwise noted. PARAMETER CONDITIONS MIN TGEN Input High Voltage TYP MAX UNITS 1.5 V TGEN Input Low Voltage 0.4 V 100 200 µA 2 2.04 V 0.
PAGE 5
LT3517 TYPICAL PERFORMANCE CHARACTERISTICS Switch Current Limit vs Temperature 2.5 VIN = 5V 103 VISP = 24V VC = 1V 102 VCTRL = 2V SWITCH CURRENT LIMIT (A) VISP – VISN THRESHOLD (mV) 104 101 100 99 98 Oscillator Frequency vs Temperature 2.5 VIN = 5V OSCILLATOR FREQUENCY (MHz) VISP – VISN Threshold vs Temperature 2.0 1.5 1.0 0.5 97 96 –40 –20 0 0 –40 –20 0 20 40 60 80 100 120 140 160 TEMPERATURE (°C) 2.02 1.7 1.
PAGE 6
LT3517 PIN FUNCTIONS SW: Switch Pin. Minimize trace at this pin to reduce EMI. SHDN: Shutdown Pin. Tie to 1.5V or higher to enable device or 0.4V or less to disable device. CTRL: LED Current Adjustment Pin. Sets voltage across sense resistor between ISP and ISN. Connect directly to VREF for full-scale threshold of 100mV, or use signal values between GND and 1V to modulate LED current. Tie the CTRL pin to the VREF pin if not used. VREF: Reference Output Pin. This pin can supply up to 100µA.
PAGE 7
LT3517 BLOCK DIAGRAM LED ARRAY CIN CFILT RSENSE PVIN ISP + ISN TG – SW PWM VISP CURRENT SENSE AMPLIFIER X10 TGEN VISP – 7V SHDN – + + CTRL 1V MOSFET DRIVER A1 ERROR AMPLIFIER + – A3 + + 1.01V A4 R + A2 FB MAIN SWITCH DRIVER S Q1 POWER SWITCH Q PWM COMPARATOR – + VC A8 SYNC RAMP GENERATOR + VIN A5 2.5MHz TO 250kHz OSCILLATOR – 1V GND – SS 100µA VREF VIN SS RT 9µA 1V + + – + A6 A7 Q2 2V FREQ ADJUST – VIN 3517 F01 Figure 1.
PAGE 8
LT3517 OPERATION The LT3517 is a constant frequency, current mode regulator with an internal power switch. Operation can be best understood by referring to the Block Diagram in Figure 1. At the start of each oscillator cycle, the SR latch is set, which turns on the Q1 power switch. A voltage proportional to the switch current is added to a stabilizing ramp and the resulting sum is fed into the positive terminal of the PWM comparator, A4.
PAGE 9
LT3517 APPLICATIONS INFORMATION than 1V, the LED current is: ILED = VCTRL 10 • RSENSE (2) When VCTRL is higher than 1V, the LED current is clamped to be: ILED = 100mV RSENSE For a buck or a buck-boost configuration, the output voltage is typically level-shifted to a signal with respect to GND, as illustrated in the Figure 4. The output can be expressed as: VOUT = R1 • 1.01V + VBE(Q1) R2 (3) R1 + VOUT The LED current programming feature possibly increases total dimming range by a factor of ten.
PAGE 10
LT3517 APPLICATIONS INFORMATION Table 1 provides some recommended inductor vendors. Table 1. Inductor Manufacturers VENDOR PHONE WEB Sumida (408) 321-9660 www.sumida.com Toko (408) 432-8281 www.toko.com Cooper (561) 998-4100 www.cooperet.com Vishay (402) 563-6866 www.vishay.com Use only ceramic capacitors with X7R, X5R or better dielectric as they are best for temperature and DC bias stability of the capacitor value.
PAGE 11
LT3517 APPLICATIONS INFORMATION Table 3. Schottky Diodes PART NUMBER VR (V) IAVE (A) 60 1 40 1 60 1.5 Diodes Inc. DFLS160 Zetex ZLLS1000TA International Rectifier 10MQ060N Board Layout The high speed operation of the LT3517 demands careful attention to board layout and component placement. The Exposed Pad of the package is the only GND terminal of the IC and is also important for thermal management of the IC.
PAGE 12
LT3517 TYPICAL APPLICATIONS Buck Mode 1A LED Driver RSENSE 100mΩ PVIN 24V VIN 3.3V C2 2.2µF C1 2.2µF L1 15µH 1A ISP VIN 2000:1 PWM Dimming at 120Hz C3 10µF M1 PWM 5V/DIV D1 ISN TG SW ILED 1A/DIV IL 1A/DIV SHDN LT3517 VREF CTRL FB PWM PWM SS SYNC RT TGEN VREF VC GND C4 0.1µF 1µs/DIV RT 16.9k 1MHz 3517 TA02b PVIN = 24V fOSC = 1MHz ILED = 1A C5 0.
PAGE 13
LT3517 TYPICAL APPLICATIONS Buck-Boost Mode LED Driver L1 6.8µH VIN 8V TO 16V SHDN VIN D1 FB R2 124k PWM 300mA PWM TGEN LT3517 ISP RSENSE 330mΩ VREF C1 2.2µF C5 0.22µF R1 3.92M SW CTRL ISN TG M1 C2 4.7µF SYNC VC C4 0.1µF RT SS RT 6.04k 2MHz GND C3 0.
PAGE 14
LT3517 TYPICAL APPLICATIONS Low Side Current Sensing Load Dump Protected Buck-Boost Mode LED Driver L1 6.8µH VIN 8V TO 16V SHDN VIN D1 C5 0.22µF R1 3.92M SW FB R2 124k PWM PWM TGEN LT3517 ISP VREF RSENSE 330mΩ CTRL C1 2.2µF TG VC R3 10k C4 33nF C2 4.7µF ISN SYNC RT SS RT 6.04k 2MHz GND M1 300mA C3 0.
PAGE 15
LT3517 TYPICAL APPLICATIONS Boost 100mA LED Driver with LED Open Protection L1 22µH VIN 8V TO 16V SHDN VIN D1 SW R1 1M FB R2 30.1k ISP PWM PWM RSENSE 1Ω TGEN VREF LT3517 ISN TG CTRL C1 2.2µF M1 SYNC VC C4 0.1µF RT 16.9k 1MHz RT SS C2 2.2µF LED1 GND LED2 100mA C3 0.
PAGE 16
LT3517 TYPICAL APPLICATION 5.5V SEPIC Converter with Short-Circuit Protection VIN 3V C2 2.2µF TG ISP LT3517 ISN TGEN RT VREF VC GND R3 10k C4 10nF R2 49.9k SS C3 0.1µF 80 R1 221k SW FB SYNC SHDN C2 10µF 90 VOUT 5.5V 350mA EFFICIENCY (%) PWM RSENSE 0.22Ω D1 L2 4.3µH VIN CTRL SHDN Efficiency C5 10µF L1 4.3µH RT 6.
PAGE 17
LT3517 PACKAGE DESCRIPTION UF Package 16-Lead Plastic QFN (4mm × 4mm) (Reference LTC DWG # 05-08-1692 Rev Ø) 0.72 ±0.05 4.35 ±0.05 2.15 ±0.05 2.90 ±0.05 (4 SIDES) PACKAGE OUTLINE 0.30 ±0.05 0.65 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS BOTTOM VIEW—EXPOSED PAD 4.00 ±0.10 (4 SIDES) 0.75 ±0.05 R = 0.115 TYP 15 PIN 1 NOTCH R = 0.20 TYP OR 0.35 × 45° CHAMFER 16 0.55 ±0.20 PIN 1 TOP MARK (NOTE 6) 1 2.15 ±0.10 (4-SIDES) 2 (UF16) QFN 10-04 0.200 REF 0.00 – 0.05 0.30 ±0.05 0.65 BSC NOTE: 1.
PAGE 18
LT3517 PACKAGE DESCRIPTION FE Package 16-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1663 Rev I) Exposed Pad Variation BA 4.90 – 5.10* (.193 – .201) 2.74 (.108) 2.74 (.108) 16 1514 13 12 1110 6.60 ±0.10 4.50 ±0.10 9 2.74 (.108) 2.74 6.40 (.108) (.252) BSC SEE NOTE 4 0.45 ±0.05 1.05 ±0.10 0.65 BSC 1 2 3 4 5 6 7 8 RECOMMENDED SOLDER PAD LAYOUT 4.30 – 4.50* (.169 – .177) 0.09 – 0.20 (.0035 – .0079) 0.25 REF 0° – 8° 0.65 (.0256) BSC 0.50 – 0.75 (.020 – .030) NOTE: 1.
PAGE 19
LT3517 REVISION HISTORY (Revision history begins at Rev C) REV DATE DESCRIPTION C 4/10 Added H-grade to Order Information Section PAGE NUMBER 2 D 7/10 Added conditions to ISP, ISN Idle Input Bias Current parameters 3 Changed VIN current sense to 9µA in Figure 1 7 E 01/11 Updated Electrical Characteristics 3 F 04/12 Subscript added to VC Pin Label 1 RT changed to RT in ABS Max Table, QFM Max Temp changed to 150°C 2 Added Operating in Note 2 4 Clarified Application Schematics G 04/
PAGE 20
LT3517 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1618 Constant Current, 1.4MHz, 1.5A Boost Converter VIN: 5V to 18V, VOUT(MAX) = 36V, Dimming = Analog/PWM, ISD < 1µA, MSOP10 Package LT3003 3-Channel LED Ballaster with PWM Dimming VIN: 3V to 48V, Dimming = 3000:1 True Color PWM, ISD < 5µA, MSOP10 Package LT3474 36V, 1A (ILED), 2MHz, Step-Down LED Driver VIN: 4V to 36V, VOUT(MAX) = 13.5V, Dimming = 400:1 True Color PWM, ISD < 1µA, TSSOP16E Package LT3475 Dual 1.