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LT3596

3596fa

Typical applicaTion

FeaTures DescripTion

60V Step-Down LED Driver

The LT

3596 is a 60V step-down LED Driver. It achieves

10,000:1 digital PWM dimming at 100Hz with fast NPN

current sources driving up to 10 LEDs in each channel.

100:1 LED dimming can also be done with analog control

of the CTRL1-3 pin.

The step-down switching frequency is programmable

between 200kHz and 1MHz and is synchronizable to an

external clock. The LT3596 also provides maximum LED

brightness while adhering to manufacturers’ specifica-

tions for thermal derating. The derate temperature is

programmed by placing a negative temperature coefficient

(NTC) resistor on the master control pin.

The LT3596 adaptively controls V

OUT

in order to achieve

optimal efficiency. Other features include: 1.5% LED current

matching between channels, open LED reporting, shorted

LED pin protection and reporting, programmable LED cur-

rent and programmable temperature protection.

48V 1MHz Step-Down 8W, 100mA LED Driver (Eight White LEDs per Channel)

applicaTions

300mA Buck Regulator, Drives Up to 10 LEDs per

Channel with Fast NPN Current Sources

Fast Current Sources for <1µs Pulse Widths

(10,000:1 True Color PWM™ Dimming at 100Hz)

LEDs Disconnected in Shutdown

Adaptive V

OUT

for Increased Efficiency

6V to 60V Input Voltage Range

±1.5% Accurate LED Current Matching

External Resistors Set LED Current for Each Channel

Requires No External Compensation

Programmable Switching Frequency (200kHz to 1MHz)

Synchronizable to External Clock

Open, Short LED Detection and Reporting

Programmable LED Thermal Derating and Reporting

Programmable Temperature Protection

5mm × 8mm Thermally Enhanced QFN Package with

0.6mm High Voltage Pin Spacing

LED Billboards and Signboards

Mono, Multi, Full Color LED Displays

Large Screen Display LED Backlighting

Automotive, Industrial and Medical Displays

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear

Technology Corporation and True Color PWM is a trademark of Linear Technology Corporation.

All other trademarks are the property of their respective owners.

EN/UVLO

LT3596

SYNCSYNC

PWM1

PWM2

PWM3

PWM1

PWM2

PWM3

CTRL1

CTRL2

CTRL3

CTRL1

CTRL2

CTRL3

FAULTFAULT

BIAS

270k

10µF

48V

91k

33.2k

REF

TSET

CTRLM

10k

90.9k

49.9k

20k 20k 20k

3696 TA01a

100k

BIAS

BOOST

GND

LED1

LED2

LED3

SET1

SET2

SET3

OUT

4.7µF

BIAS

z28V

PER LED

STRING

4.7µF

OUT

100nF

100k

3.65k

100µH

10,000:1 PWM Dimming at 100Hz

PWM

2V/DIV

LED

50mA/DIV

200ns/DIV

3596 TA01b

Summary of content (22 pages)

PAGE 1
LT3596 60V Step-Down LED Driver Features n n n n n n n n n n n n n n Description 300mA Buck Regulator, Drives Up to 10 LEDs per Channel with Fast NPN Current Sources Fast Current Sources for <1µs Pulse Widths (10,000:1 True Color PWM™ Dimming at 100Hz) LEDs Disconnected in Shutdown Adaptive VOUT for Increased Efficiency 6V to 60V Input Voltage Range ±1.
PAGE 2
LT3596 BOOST DA TOP VIEW SW Input Voltage (VIN), EN/UVLO . .................................60V BOOST ......................................................................80V BOOST Pin Above SW Pin ....................................... 25V LED1-3, VOUT.............................................................42V BIAS, FAULT ..............................................................25V VREF, RT, ISET1-3, TSET, CTRLM . ................................3V FB, CTRL1-3, PWM1-3, SYNC ................
PAGE 3
LT3596 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 24V, BOOST = 30V, BIAS = 5V, EN/UVLO = 5V, PWM1-3 = 3.3V, CTRL1-3 = CTRLM = TSET = 2V, VOUT = 24V, SYNC = 0V unless otherwise specified. (Note 2) PARAMETER CONDITIONS VIN Operating Voltage Quiescent Current from VIN MIN l EN/UVLO = 0.
PAGE 4
LT3596 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 24V, BOOST = 30V, BIAS = 5V, EN/UVLO = 5V, PWM1-3 = 3.3V, CTRL1-3 = CTRLM = TSET = 2V, VOUT = 24V, SYNC = 0V unless otherwise specified. (Note 2) PARAMETER CONDITIONS MIN TYP PWM1-3 Input Low Voltage 0.4 PWM1-3 Input High Voltage 1.6 200 CTRL1-3 Voltage for Full LED Current 1.2 200 1.
PAGE 5
LT3596 Typical Performance Characteristics VIN Quiescent Current 2.0 BIAS Quiescent Current 2.0 VBIAS = 5V 1.8 VIN = 24V 1.0 0.8 0.6 1.0 0.5 0 10 30 40 20 VIN VOLTAGE (V) 50 0.6 –0.5 60 T = 125°C T = 25°C T = –40°C 5 0 15 10 BIAS VOLTAGE (V) 20 0.2 UVLO Threshold 0 –50 –25 25 6 1.7 2.04 VEN/UVLO = 1.4V 1.3 1.2 4 3 2 0 50 75 25 TEMPERATURE (°C) 100 0 –50 –25 125 50 25 75 0 TEMPERATURE (°C) 3596 G04 Switching Frequency 1.2 1000 CURRENT LIMIT (mA) RT = 33.2k 0.8 0.6 0.
PAGE 6
LT3596 Typical Performance Characteristics Boost Diode Voltage TA = 25°C, unless otherwise noted Soft-Start 60V Buck Switching Waveforms BOOST DIODE VOLTAGE (V) 1.0 0.8 EN/UVLO 5V/DIV 0.6 SW 50V/DIV IL 500mA/DIV 0.4 IL 500mA/DIV VOUT 20V/DIV VOUT 20V/DIV 0.2 0 SW 20V/DIV 400µs/DIV 0 25 50 75 100 125 CURRENT (mA) 150 3596 G11 400ns/DIV 3596 G12 175 3596 G10 LED Current 1.4 103 1.3 102 VFB 1.2 VLED 1.1 RISETn = 20k 0.50 101 100 0.25 0 –0.25 99 LED1 LED2 LED3 98 0.
PAGE 7
LT3596 Typical Performance Characteristics 10,000:1 PWM Dimming at 100Hz TA = 25°C, unless otherwise noted PWM Dimming Waveforms (Overlapping PWM Signals) 1,000:1 PWM Dimming at 100Hz PWM1 5V/DIV PWM 2V/DIV PWM 2V/DIV ILED 50mA/DIV ILED 50mA/DIV ILED1 100mA/DIV PWM2 5V/DIV ILED2 100mA/DIV 200ns/DIV 3596 G19 3596 G20 2µs/DIV PWM Dimming Waveforms (Nonoverlapping PWM Signals) LED Open-Fault Waveforms PWM1 5V/DIV LED Short to VOUT Waveforms VOUT 20V/DIV VLED 20V/DIV VLED 1V/DIV ILED1 100mA/DIV
PAGE 8
LT3596 Pin Functions FB (Pin 2): Feedback Pin. This pin is regulated to the internal bandgap voltage. The maximum buck output voltage is set by connecting this pin to a resistor divider from VOUT . EN/UVLO (Pin 4): Enable and Undervoltage Lockout Pin. Accurate 1.5V falling threshold. UVLO threshold is programmed by using a resistor divider from VIN. TSET (Pin 6): Thermal Regulation Pin. Programs the LT3596 junction temperature at which LED current begins to derate. VREF (Pin 7): 2V Reference Output Pin.
PAGE 9
LT3596 Block Diagram VIN 50-51 4 7 27 17 EN/UVLO BIAS START-UP REFERENCE VREF + – BIAS BOOST SYNC OSC RT S SW SLOPE COMP VC 540mV PTAT 6 13 TSET CTRLM CTRLn 33-31 + – 1.21V + – 1V DA + GND FB VOUT FAULT LED FAULT PROTECTION CONVERSION AND CONTROL ISETn 14-16 PWMn 30-28 – CHANNELS 1 TO 3 – + 46 Q R SOFT-START AND CLAMP 37 LED DRIVE CIRCUITRY PWM DIMMING LOGIC 48 44 9 2 19 25 LOGIC LEDn 20, 21, 24 EXPOSED PAD 53 3596 F01 Figure 1.
PAGE 10
LT3596 Operation The LT3596 uses a constant-frequency, peak current mode control scheme to provide excellent line and load regulation. Operation is best understood by referring to the Block Diagram (Figure 1). The bias, start-up, reference, oscillator, TSET amplifier and the buck regulator are shared by the three LED current sources. The conversion and control, PWM dimming logic, LED fault detection, and LED drive circuitry are identical for all three current sources.
PAGE 11
LT3596 Applications Information Inductor Selection Inductor values between 100µH and 470µH are recommended for most applications. It is important to choose an inductor that can handle the peak current without saturating. The inductor DCR (copper wire resistance) must also be low in order to minimize I2R power losses. Table 1 lists several recommended inductors. Typically 10µF capacitors are sufficient for the VIN and BIAS pins.
PAGE 12
LT3596 Applications Information LED Current Dimming LT3596 The LT3596 has two different types of dimming control. The LED current is dimmed using the CTRLn pin or the PWMn pin. EN/UVLO R1 + – R2 1.51V 3596 F02 Figure 2. EN/UVLO Control In UVLO an internal 5.1µA (typical) pull-down current source is connected to the pin for programmable UVLO hysteresis. The hysteresis is set according to the following equation: VUVLO(HYST) = 5.
PAGE 13
LT3596 Applications Information For True Color PWM dimming, the LT3596 provides up to 10,000:1 PWM dimming range at 100Hz. This is done by reducing the duty cycle of the PWMn pin from 100% to 0.01% for a PWM frequency of 100Hz (see Figure 5). This equates to a minimum on time of 1µs and a maximum period of 10ms. PWM duty cycle dimming allows for constant LED color to be maintained over the entire dimming range. LT3596 TSET R1 3596 F06 Figure 6. Programming the TSET Pin Table 6.
PAGE 14
LT3596 Applications Information 100 RISETn = 20k RX RX R2 LT3596 RX RNTC RNTC RNTC CTRLM R1 (OPTION A TO D) RX 3596 F08 (8a) (8b) (8c) (8d) 75 LED CURRENT (mA) VREF 50 25 Figure 8. Programming the CTRLM Pin LED currents to be controlled by the CTRLM pin voltage. The LED current-curve breakpoint and slope versus temperature are defined by the choice of resistor ratios and use of temperature-dependent resistance in the divider for the CTRLM pin.
PAGE 15
LT3596 Applications Information losses. Some applications require very low duty cycles to drive a small number of LEDs from a high supply. Low switching frequency allows a greater range of operational duty cycle and so a lower number of LEDs can be driven. In each case, the switching frequency can be tailored to provide the optimum solution. When programming the switching frequency, the total power losses within the IC should be considered. Table 8.
PAGE 16
LT3596 Applications Information The maximum output voltage must be set to exceed the maximum LED drop plus 1.07V by a margin greater than 15%. However, this margin must not exceed a value of 10V. This ensures proper adaptive loop control. The equation below is used to estimate the resistor divider ratio. The sum of the resistors should be approximately 100k to avoid noise coupling to the FB pin. ( )  R2  VOUT(MAX ) = 1.15 • VLED(MAX ) + 1.07 V = 1.21V •  1+   R1 VOUT(MAX) = VLED(MAX) + 1.
PAGE 17
LT3596 Typical applications 24V 200kHz Step-Down 4W, 100mA LED Driver VIN 24V VIN 10µF BIAS EN/UVLO BOOST 91k LT3596 SW SYNC RT SYNC VOUT 10µF 100k 7.32k FB PWM1 PWM2 PWM3 PWM1 PWM2 PWM3 CTRL1 CTRL2 CTRL3 CTRL1 CTRL2 CTRL3 BIAS VOUT 100k FAULT VREF LED1 LED2 LED3 TSET CTRLM ISET1 ISET2 ISET3 FAULT 10k 100k MURATA NCP18WF104 z 13.5V PER LED STRING 3696 TA02a 20k 20k 20k Efficiency 100 80 EFFICIENCY (%) 49.9k 100nF 470µH DA GND 220k 90.
PAGE 18
LT3596 Typical applications 12V 1MHz Step-Down 100mA Single Pixel R-G-B Driver VIN 12V VIN 10µF BIAS EN/UVLO BOOST 91k LT3596 SW SYNC SYNC RT PWM1 PWM2 PWM3 CTRL1 CTRL2 CTRL3 CTRL1 CTRL2 CTRL3 49.9k 14.7k VOUT 100k FAULT VOUT 6.8µF 100k FB PWM1 PWM2 PWM3 BIAS 100nF 100µH DA GND 33.2k 90.
PAGE 19
LT3596 Typical applications 48V 500kHz Step-Down 10W, 100mA LED Driver VIN 48V 10µF VIN BIAS 4.7µF 270k EN/UVLO BOOST 91k LT3596 100nF 220µH SW SYNC SYNC RT 80.6k 5V BIAS DA GND VOUT 6.8µF 100k 3.01k FB PWM1 PWM2 PWM3 PWM1 PWM2 PWM3 CTRL1 CTRL2 CTRL3 CTRL1 CTRL2 CTRL3 VOUT z 36V PER LED STRING BIAS 100k FAULT 90.9k 49.
PAGE 20
LT3596 Package Description UHG Package Variation: UHG52 (39) 52-Lead Plastic QFN (5mm × 8mm) (Reference LTC DWG # 05-08-1846 Rev B) 43 41 39 6.40 REF 35 34 33 32 31 30 29 28 37 27 0.70 p 0.05 44 26 25 24 46 5.50 p 0.05 4.10 p 0.05 23 48 22 3.20 REF 21 2.90 p0.05 50 20 5.90 p0.05 51 19 18 PACKAGE OUTLINE 2 4 6 0.80 BSC 7 9 11 12 13 14 15 16 0.40 BSC 17 0.20 p 0.05 7.10 p 0.05 8.50 p 0.
PAGE 21
LT3596 Revision History REV DATE DESCRIPTION PAGE NUMBER A 9/10 Added “≈ 28V per LED String” to Typical Application drawing 1, 22 Added text and equations to Adaptive Loop Control section in Applications Information 16 Added “≈ 13.5V per LED String” and “≈ 8V per LED String” to Typpplications drawings 17 3596fa Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use.
PAGE 22
LT3596 Typical Application 48V 1MHz Step-Down 8W, 100mA LED Driver (Eight White LEDs per Channel) VIN 48V VIN 10µF BIAS EN/UVLO BOOST 91k SW 33.2k PWM1 PWM2 PWM3 CTRL1 CTRL2 CTRL3 CTRL1 CTRL2 CTRL3 100k FAULT 100k 4.7µF 3.65k z 28V PER LED STRING FAULT VOUT 10k TSET CTRLM LED1 LED2 LED3 200ns/DIV 3596 TA01b 3696 TA01a ISET1 ISET2 ISET3 100k 49.9k PWM 2V/DIV ILED 50mA/DIV VREF 90.