LT3754

LT3597 LINER

Document overview

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Technical content

DESCRIPTION

The L T®3597 is a 60V triple step-down LED driver capable of achieving 10,000:1 digital PWM dimming at 100Hz with fast NPN current sources driving up to 10 LEDs in each channel. LED dimming can also be achieved via analog control of the CTRL1-3 pin. The step-down switching frequency is programmed be - tween 200kHz and 1MHz. The frequency is also synchroniz- able to an external clock. The L T3597 provides maximum LED brightness while adhering to manufacturers’ speci - fications for thermal derating. The derate temperature is programmed by placing a negative temperature coefficient (NTC) resistor on the master control pin. The L T3597 adaptively controls V OUT in order to achieve optimal efficiency. Other features include: 2% LED cur - rent matching between channels, open LED reporting, shorted LED protection, programmable LED current, and programmable temperature protection. L, L T , L TC and L TM are registered trademarks of Linear Technology Corporation. T rue Color PWM is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. T riple Step-Down RGB Single Pixel LED Driver , 100mA Current

FEATURES

APPLICATIONS

n Three 100mA Buck Regulators, Each Drives Up to

10 LEDs with Fast NPN Current Sources

n Fast Current Sources for <1µs Pulse Widths (10,000:1 T rue Color PWM™ Dimming at 100Hz) n LEDs Disconnected in Shutdown n Adaptive VOUT for Increased Efficiency n 6V to 60V Input Voltage Range n ±2% LED Current Matching n External Resistor Sets LED Current for Each Channel n Internal Compensation and Soft-Start n Programmable Switching Frequency (200kHz to 1MHz) n Synchronizable to External Clock n Open LED Detection and Reporting n Shorted LED Pin Protection and Reporting n Programmable LED Thermal Derating n Programmable Temperature Protection n 5mm × 8mm Thermally Enhanced QFN Package with a 0.6mm High Voltage Pin Spacing n LED Billboards and Signboards n Mono, Multi, Full-Color LED Displays n Large Screen Display LED Backlighting n Automotive, Industrial, and Medical Displays 10,000:1 PWM Dimming at 100Hz

3597 TA01a

V OUT1 LED1 BIAS FAUL T PWM1-3 CTRL1-3 SYNC RT BOOST2 SW2 DA2 FB2 V OUT2 LED2 BOOST3 SW3 DA3 FB3 VOUT3 LED3 VREF TSET CTRLM L T3597 9.1kR 100k 97k 91k 270k 3.3µF 0.1µF 10µF 100µH 0.1µF 3.3µF 100µH 9.1k 97k 0.1µF 3.3µF 100µH 9.1k 97k 100k 10k 82.5k VREF 49.9k 10µF VCC VOUT1 VIN 48V 33.2k (1MHz) ISET1 ISET2 ISET3 GND 20k 20k 20k VOUT2 VOUT3 G B ILED 50mA/DIV PWM 2V/DIV

3597 TA01b

PIN CONFIGURATIONABSOLUTE MAXIMUM RATINGS Operating Junction Temperature Range (Note 1) 18 19 20 21 TOP VIEW GND UHG PACKAGE VARIATION: UHG52(39) 52-LEAD (5mm × 8mm) PLASTIC QFN 22 23 24 25 26 51 50 48 46 44 2BST1 SW1 DA1 FB1 EN/UVLO TSET VREF CTRLM ISET1 ISET2 ISET3 RT DA3 SW3 BST3 BIAS FB3 FB2 CTRL1 CTRL2 CTRL3 PWM1 PWM2 PWM3 SYNC VIN VIN BST2 SW2 DA2 GND V OUT1 LED1 LED2 VOUT2 VOUT3 LED3 FAUL T NC TJMAX = 125°C, θJA = 32°C/W EXPOSED PAD (PIN 53) IS GND, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE L T3597EUHG#PBF L T3597EUHG#TRPBF 3597 52-Lead (5mm × 8mm) Plastic QFN –40°C to 125°C L T3597IUHG#PBF L T3597IUHG#TRPBF 3597 52-Lead (5mm × 8mm) Plastic QFN –40°C to 125°C Consult L TC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container . Consult L TC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear .com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear .com/tapeandreel/

ELECTRICAL CHARACTERISTICS

PARAMETER CONDITIONS MIN TYP MAX UNITS VIN Operating Voltage l 6 55 V Quiescent Current from VIN EN/UVLO = 0.4V BIAS = 5V , Not Switching BIAS = 0V , Not Switching 2.1 µA mA mA Minimum BIAS Voltage 3 3.1 V Quiescent Current from BIAS EN/UVLO = 0.4V BIAS = 5V , Not Switching BIAS = 0V , Not Switching, Current Out of Pin 150 µA mA µA EN Threshold (Falling) 0.4 0.7 V UVLO Threshold (Falling) 1.47 1.51 1.53 V EN/UVLO Pin Current (Hysteresis) EN/UVLO = 1.6V EN/UVLO = 1.4V 5.1 nA µA FB1-3 Regulation Voltage 1.15 1.22 1.25 V FB1-3 Pin Bias Current FB = 6V 200 nA Maximum Duty Cycle R T = 220k (200kHz) RT = 33.2k (1MHz) Switch Saturation Voltage I SW1-3 = 100mA 265 mV Switch Current Limit 400 510 700 mA DA Pin Current to Stop OSC 225 280 350 mA Switch Leakage VSW1-3 = 0V 700 nA BST1-3 Pin Current ISW1-3 = 100mA 2 mA Switching Frequency RT = 220k RT = 33.2k 170 900 200 1000 230 1100 kHz kHz SYNC Input Low 0.4 V SYNC Input High 1.6 V SYNC Frequency Range R T = 220k RT = 47k 240 1000 kHz kHz SYNC Pin Bias Current V SYNC = 3.3V 200 nA Soft-Start Time (Note 4) 2.5 ms VREF Voltage IVREF = 0µA l 1.96 2.0 2.04 V Maximum VREF Current 200 µA ISET1-3 Pin Voltage RISET1-3 = 20k, VCTRL = VCTRLM = TSET = 1.5V 1.0 V TSET Voltage for LED Current Derating 540 mV TSET Pin Leakage Current VTSET = 1.0V 200 nA ILED1-3 LED Current RISET1-3 = 20k l 100 100 102 103 mA mA The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 24V , BOOST = 29V , BIAS = 5V , EN/UVLO = 5V , PWM1-3 = 3.3V , CTRL1-3 = CTRLM = TSET = 2.0V , VOUT1-3 = 24V , SYNC = 0V , unless otherwise specified. (Note 2)

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 = 29V , BIAS = 5V , EN/UVLO = 5V , PWM1-3 = 3.3V , CTRL1-3 = CTRLM = TSET = 2.0V , VOUT1-3 = 24V , SYNC = 0V , unless otherwise specified. (Note 2) PARAMETER CONDITIONS MIN TYP MAX UNITS LED String Current Matching RISET1-3 = 20k l ±0.35 ±0.35 ±1.5 LED Pin Voltage Adaptive V OUT Loop Enabled 1.1 V LED1-3 Open Detection Threshold 0.28 V LED1-3 Short Protection Threshold (from GND) PWM1-3 = 3.3V 10 15 V LED1-3 Short Protection Threshold (from VOUT1-3) VOUT1-3 = 6V 1 1.25 2 V LED1-3 Pin Leakage Current VLED1-3 = 42V 100 nA PWM1-3 Input Low Voltage 0.4 V PWM1-3 Input High Voltage 1.6 V PWM1-3 Pin Bias Current 200 nA CTRL1-3 Voltage for Full LED Current 1.2 V CTRL1-3 Pin Bias Current CTRL1-3 = 6V 200 nA CTRLM Voltage for Full LED Current 1.2 V CTRLM Pin Bias Current CTRLM = 3V 200 nA FAUL T Output Voltage Low IFAUL T = 200µA 0.11 V FAUL T Pin Input leakage Current FAUL T = 25V 200 nA Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The L T3597E is guaranteed to meet performance specifications from 0°C to 125°C junction temperature. Specifications over the –40°C to 125°C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. The L T3597I specifications are guaranteed over the full –40°C to 125°C operating junction temperature range. Note 3: For Maximum Operating Ambient Temperature, see Thermal Considerations in the Applications Information section. Note 4: Guaranteed by design.

TYPICAL PERFORMANCE CHARACTERISTICS UVLO Threshold Voltage (Falling) EN/UVLO Pin Bias Current VREF Voltage Switching Frequency Current Limit Switch Voltage Drop VIN Quiescent Current VBIAS Quiescent Current Shutdown Current TA = 25°C, unless otherwise noted. VIN CURRENT (mA) 1.0 1.5 0.5 40 60

3597 G01

2.0 3.0 2.5 3010 20 50 VIN VOL TAGE (V) –40°C 25°C VBIAS = 5V 125°C VBIAS CURRENT (mA)1.0 1.5 0.5 15 25

3597 G02

–0.5 2.0 3.0 2.5 10 5 20 VBIAS VOL TAGE (V) 125°C VIN = 24V –40°C 25°C –50 CURRENT (µA) 1.00 1.25 0.50 0.75 0.25 75 125

3597 G03

1.50 2.00 1.75 50 25 0 –25 100 TEMPERATURE (°C) IBIAS IVIN VIN = 55V VBIAS = 25V –50 UVLO VOLTAGE (V) 1.4 1.5 1.2 1.3 1.1 1.0 75 125

3597 G04

1.6 1.8 1.7 50 25 0 –25 100 TEMPERATURE (°C) –50 CURRENT (µA) 75 125

3597 G05

50 25 0 –25 100 TEMPERATURE (°C) EN/UVLO = 1.4V EN/UVLO = 1.6V –50 VREF VOLTAGE (V) 2.02 2.03 2.00 2.01 1.99 1.98 1.97 75 125

3597 G06

1.96 2.04 50 25 0 –25 100 TEMPERATURE (°C) VIN = 6V VIN = 55VVIN = 24V VREF LOAD = 0µA –50 FREQUENCY (MHz) 0.8 1.0 0.6 0.4 0.2 75 125

3597 G07

1.2 50 25 0 –25 100 TEMPERATURE (°C) RT = 33.2k RT = 220k –50 CURRENT (mA) 400 500 300 200 100 75 125

3597 G08

50 25 0 –25 100 TEMPERATURE (°C) DA SWITCH SWITCH VOLTAGE DROP (mV) 400 500 300 200 100 250

3597 G09

SWITCH CURRENT (mA) –40°C 25°C VBIAS = 5V 125°C

TYPICAL PERFORMANCE CHARACTERISTICS Loop Regulation Voltage LED Current LED Current Matching LED Current vs PWM Duty Cycle LED Current vs CTRL Adaptive Loop Operation Boost Diode VF Soft-Start 60V Switching Waveforms TA = 25°C, unless otherwise noted. DIODE VF (mV) 400 500 600 700 300 200 100

3597 G10

DIODE CURRENT (mA) –40°C 25°C 125°C VOUT 20V/DIV IL 100mA/DIV VSW 20V/DIV VEN/UVLO 5V/DIV

3597 G11

400µs/DIV VOUT 20V/DIV IL 100mA/DIV VSW 20V/DIV

3597 G12

–50 VOLTAGE (V)1.1 1.2 1.0 75 125

3597 G13

0.9 1.4 1.3 50 25 0 –25 100 VFB TEMPERATURE (°C) VLED (ADAPTIVE LOOP) –50 LED CURRENT (mA)99 100 75 125

3597 G14

50 25 0 –25 100 CH2 CH3 TEMPERATURE (°C) CH1 –50 LED CURRENT MATCHING (%) 0.25 –0.25 75 125

3597 G15

–0.50 0.50 50 25 0 –25 100 CH2 CH3 TEMPERATURE (°C) CH1 0.001 LED CURRENT (mA) 0.1 0.01 0.001 100

3597 G16

0.0001 100 10 1 0.10.01 DUTY CYCLE (%) LED CURRENT (mA) 1.5

3597 G17

1.25 1 0.75 0.5 0.25 CTRL VOL TAGE (V) VOUT 10V/DIV VLED 10V/DIV ILED 100mA/DIV VSW 20V/DIV

3597 G18

400µs/DIV

TYPICAL PERFORMANCE CHARACTERISTICS Shorted LEDs Fault FAUL T Pin Voltage Low TSET Voltage for Temperature Derating TSET LED Current Derating 20,000:1 PWM Dimming (100Hz) 1,000:1 PWM Dimming (100Hz) Open LED Fault TA = 25°C, unless otherwise noted. ILED 50mA/DIV PWM 2V/DIV

3597 G19

3597 G20

2µs/DIV VFAULT 5V/DIV ILED 100mA/DIV VLED 2V/DIV VOUT 5V/DIV

3597 G21

3597 G22

FAUL T PIN VOLTAGE (mV)100 150 0.6 1

3597 G23

0.40.2 0.8 FAUL T PIN CURRENT (mA) 125°C 25°C 40°C –50 TSET VOLTAGE (V) 0.4 0.5 75 125

3597 G24

0.3 0.8 0.6 0.7 50 25 0 –25 100 TEMPERATURE (°C) LED CURRENT (mA)40 65 85 125

3597 G25

TEMPERATURE (°C) VTSET = 0.675V

BOOST1, BOOST2, BOOST3 (Pins 2, 48, 39): Boost Capacitor Pin. This pin is used to provide a voltage that is higher than the input voltage when the switch is on to supply current to the switch driver . SW1, SW2, SW3 (Pins 4, 46, 41): Switch Pin. Connect the inductor , catch diode and boost capacitor to this pin. DA1, DA2, DA3 (Pins 6, 44, 43): Catch Diode Anode. This pin is used to provide frequency foldback in extreme situations. FB1, FB2, FB3 (Pins 7, 34, 35): Feedback Pin. This pin is regulated to the internal bandgap voltage. The maximum Buck output voltage can be set by connecting this pin to a resistor divider from VOUT1-3. EN/UVLO (Pin 9): Enable and Undervoltage Lockout Pin. Accurate 1.51V threshold. UVLO threshold can be pro - grammed by using a resistor divider from V IN. If function is not required, pin can be tied to the VIN pin. T SET (Pin 11): Thermal Regulation Pin. Programs the L T3597 junction temperature at which LED current begins to derate. VREF (Pin 12): 2.0V Reference Output Pin. This pin can sources up to 200µA and can be used to program TSET and CTRLM. CTRLM (Pin 13): Master Control Pin. LED current derating vs temperature is achievable for all channels if the voltage on CTRLM has a negative temperature coefficient using an external NTC resistor in a voltage divider from VREF. I SET1, ISET2, ISET3 (Pins 14, 15, 16): LED Current Pro- gramming Pin. A resistor to ground programs full-scale LED current. RT (Pin 17): Switching Frequency Programming Pin. A resistor to ground programs the switching frequency between 200kHz and 1MHz. GND (Pin 18, Exposed Pad Pin 53): Ground Pin. This is the ground for both the IC and the switching converters. Exposed pad must be soldered to PCB ground. V OUT1, VOUT2, VOUT3 (Pins 19, 22, 23): Buck Output. This is the buck regulator output voltage sense into the IC. LED1, LED2, LED3 (Pins 20, 21, 24): Constant Current Sink Pin. These are 3 LED driver outputs, each containing an open collector , constant current sink. All outputs are matched within ±2% and are individually programmed up to 100mA using an external resistor at the ISET1-3 pin. Outputs are rated to allow a maximum VOUT1-3 of 42V . Connect the cathode of the LED string to LED1-3. Connect the anode of the LED string to VOUT1-3. FAUL T (Pin 25): Fault Detection Pin. Open collector pin used to report open LED faults. FAUL T must be externally pulled to a positive supply through a resistor . NC (Pin 26): No Connection Pin. Tie to ground. SYNC (Pin 27): External Clock Synchronization Pin. When an external clock drives this pin, the Buck regulators are synchronized to that frequency. Frequency programmed by the RT pin resistor must be at least 20% less than the SYNC pin clock frequency. PWM1, PWM2, PWM3 (Pins 30, 29, 28): PWM Dimming Control Pin. When driven to a logic high, the LED1-3 current sink is enabled. If PWM dimming is not desired, connect the pin to VREF. Channels can be individually disabled by tying PWM1-3 to ground. CTRL1, CTRL2, CTRL3 (Pins 33, 32, 31): Analog Dimming Control Pin. This pin is used to dim the LED current in an analog fashion. If the pin is tied to a voltage lower than 1.0V , it will linearly reduce the LED current. If feature is unused, connect the pin to VREF . BIAS (Pin 37): Supply Pin. This pin is the supply for an internal voltage regulator to internal analog and digital circuitry. BIAS must be locally bypassed with a 2.2µF capacitor . V IN (Pins 50, 51): Input Supply Pin. VIN must be locally bypassed with a 10µF capacitor to ground. Pins 50 and 51 are internally fused.

Figure 1. Block Diagram

The L T3597 uses a constant frequency, internally com- pensated peak current mode control scheme. Operation is best understood by referring to the Block Diagram in Figure 1. Enable and undervoltage lockout (UVLO) are both con - trolled by a single pin. If the pin falls below 1.51V , an accurate comparator turns off the LED drivers and buck regulators. If the pin continues to fall to less than 0.4V , the part enters shutdown and consumes less than 2µA. The L T3597 contains three constant current sink LED drivers. Each of the three LED strings is powered from a dedicated adaptive buck converter in order to achieve maximum efficiency. The frequency of the buck regulators is programmed from 200kHz to 1MHz using an external resistor . The frequency can also be synchronized to an external clock using the SYNC pin. Internal buck compensation and soft-start requires few external components and permits simple board layout. A high-side switch current limit protects the internal switch during its on time, while a low side current limit prevents the switch from turning on in the case of excessive off phase current. Step-Down Adaptive Control Adaptive control of the output voltages achieves superior system efficiency. When a given channel’s PWM pin is low, the respective buck regulator output will go to a programmable high output voltage. In this case the buck will enter into a pulse-skipping mode since there is no load connected. This guarantees that the buck output voltage is high enough to immediately supply the LED current once the string is reactivated. As soon as PWM goes high, the output voltage of the buck will drop until there is 1V across the LED current sink. This scheme ensures the best efficiency for each LED channel. Since each LED string is independently driven from a separate buck chan- nel, efficiency is optimized for all three strings even if the number of LEDs is mismatched between the channels. Another benefit of this regulation method is that the L T3597 starts up with 10,000:1 dimming even if the PWM1-3 pulse width is 1µs. Since V OUT starts up even if PWM1-3 is low, the part achieves high dimming ratios with narrow pulse widths within a couple of PWM1-3 clock cycles. LED Current Each LED string current can be individually programmed up to a maximum of 100mA with a 2% matching accuracy between the strings. An external resistor on the I SET1-3 pin programs the max current for that string. The CTRL1-3 pin can be used for analog dimming. Digital PWM can be programmed using the PWM1-3 pin. A dimming ratio of 10,000:1 can be achieved at a frequency of 100Hz. Fault Protection and Reporting The L T3597 protects against both open LED and shorted LED conditions. If the LED1-3 pin voltage exceeds 12V while the LED string is sinking current, or if the LED1-3 pin voltage is within 1.25V of V OUT1-3 pin voltage, the channel is disabled until the fault is removed. If the LED string opens, the L T3597 will limit the output to the voltage set by the FB resistor divider . The L T3597 reports a fault on the FAUL T pin if any of the LED strings is open or shorted. LED faults are only reported if the respective string PWM signal is high. A fault is also reported if the internal die temperature reaches the T SET programmed derating limit.

Table 1 lists several recommended inductors. Table 1. Recommended Inductors be used at the outputs to minimize output ripple voltage. Table 2. Recommended Ceramic Capacitor Manufacturers Table 3 for the proper output capacitor selection. Table 3. Recommended Output Capacitor Values (VLED = 3.5V) recommended Schottky diodes. Table 4. Recommended Diodes

IN pin as shown in Figure 2. resistor (RISET1-3) between the ISET1-3 pin and ground. sponding programmed LED current. Table 5. LED Current Programming Figure 3. RISET1-3 Value for LED Current

3597 F03

Figure 2. EN/UVLO Control

3597 F02

Figure 4. LED Current vs CTRL1-3 Voltage Figure 5. LED Current Using PWM Dimming

3597 F04

CTRL1-3 pin or the PWM1-3 pin. under worst-case conditions. part junction temperature as shown in Figure 6.

3597 F06

Figure 6. Programming the TSET Pin

3597 F07

Table 6 shows commonly used values for R1 and R2. temperature limit as described in Figure 7. Table 6. TSET Programmed Junction Temperature tection feature is not desired. Figure 8. Programming the CTRLM Pin divider with temperature dependent resistance (Figure 8). LED currents to be controlled by the CTRLM pin voltage.

3597 F08

Figure 7. TSET Voltage for Temperature Derating

3597 F09

tor is placed as closely as possible to the LED strings. found using the curve shown in Figure 9. Table 7. NTC Resistor Manufacturers/Distributors NTC resistor over temperature. Figure 10. Programming Switching Frequency with complete data over a wide range of temperatures. derating function is not desired. and corresponding frequencies. Table 8. RT Resistor Selection

3597 F10

Figure 9. LED Current vs CTRLM Voltage

losses within the IC should be considered. at a fixed delay after the rising edge of SYNC. Figure 11. Programming Maximum VOUT1-3 duced until the voltage across the LED current sink is 1V . be set by an external resistor divider .

3597 F11

The maximum output voltage must be set to exceed the maximum LED drop plus 1V by a margin greater than 10%. However , this margin must not exceed a voltage of 10V . This ensures proper adaptive loop control. The equations below are used to estimate the resistor divider ratio. The sum of the resistors should be less than 100k to avoid noise coupling to the FB pin. VOUT(MAX) = 1.1 VLED(MAX) + 1.1V( )= 1.2V • 1+ R2   VOUT(MAX) = VLED(MAX) +1.1V + VMARGIN VMARGIN ≤ 10V Minimum Input Voltage The minimum input voltage required to generate an output voltage is limited by the maximum duty cycle and the output voltage (V OUT) set by the FB resistor divider . The duty cycle is: DC = VD + VOUT VIN − VCESAT + VD where VD is the Schottky forward drop and VCESAT is the saturation voltage of the internal switch. The minimum input voltage is: VIN(MIN) = VD + VOUT(MAX) DCMAX  + VCESAT − VD where VOUT(MAX) is calculated from the equation in the Adaptive Loop Control section, and DCMAX is the minimum rating of the maximum duty cycle. Fault Flag The FAUL T pin is an open-collector output and needs an external resistor tied to a supply. If the LED1-3 pin volt - age exceeds 12V or if the LED1-3 pin voltage is within 1.25V of VOUT1-3 pins while PWM1-3 is high, the FAUL T pin will be pulled low. The FAUL T pin will also be pulled low if the internal junction temperature exceeds the T SET programmed temperature limit. There is a 3µs delay for FAUL T flag generation when the PWM1-3 signal is enabled to avoid generating a spurious flag signal. The maximum current the FAUL T can sink is typically 1mA. Thermal Considerations The L T3597 provides three channels for LED strings with internal NPN devices serving as constant current sources. When LED strings are regulated, the lowest LED pin volt- age is typically 1V . More power dissipation occurs in the L T3597 at higher programmed LED currents. For 100mA of LED current with a 100% PWM dimming ratio, at least 300mW is dissipated within the IC due to current sources. Thermal calculations must include the power dissipation in the current sources in addition to conventional switch DC loss, switch transient loss and input quiescent loss. In addition, the die temperature of the L T3597 must be lower than the maximum rating of 125°C. This is generally not a concern unless the ambient temperature is above 100°C. Care should be taken in the board layout to ensure good heat sinking of the L T3597. The maximum load current should be derated as the ambient temperature ap- proaches 125°C. The die temperature rise above ambient is calculated by multiplying the L T3597 power dissipation by the thermal resistance from junction to ambient. Power dissipation within the L T3597 is estimated by calculating the total power loss from an efficiency measurement and subtracting the losses of the catch diode and the inductor . Thermal resistance depends on the layout of the circuit board, but 32°C/W is typical for the 5mm × 8mm QFN package.

As with all switching regulators, careful attention must be paid to the PCB board layout and component placement. To prevent electromagnetic interference (EMI) problems, proper layout of high frequency switching paths is essen- tial. Minimize the length and area of all traces connected to the switching node pin (SW). Always use a ground plane under the switching regulator to minimize inter- plane coupling. Good grounding is essential in LED fault detection. Proper grounding is also essential for the external resistors and resistor dividers that set critical operation parameters. Both the L T3597 exposed pad and pin 18 are ground. Resistors connected between ground and the CTRL1-3, CTRLM, FB1-3, T SET, ISET1-3, RT and EN/UVLO pins are best tied to pin 18 and not the ground plane. APPLICATIONS INFORMATION

48V 1MHz T riple Step-Down 100mA RGB LED Driver Efficiency

3597 TA02

V OUT1 LED1 BIAS FAUL T PWM1-3 CTRL1-3 SYNC RT BOOST2 SW2 DA2 FB2 V OUT2 LED2 BOOST3 SW3 DA3 FB3 VOUT3 LED3 VREF TSET CTRLM L T3597 9.1k 100k 97k 91k 270k 3.3µF 0.1µF 10µF 100µH 0.1µF 2.2µF 100µH 4.7k 97k 0.1µF 2.2µF 100µH 3.83k 97k 100k 10k 82.5k VREF 49.9k 10µF VCC VIN 48V VOUT1 33.2k ISET1 ISET2 ISET3 GND 20k 20k 20k VOUT2 VOUT3 (1MHz) R B G LED CURRENT PER CHANNEL (mA) 0 10 EFFICIENCY (%) 60 50 80 7040 30 20

3597 TA02b

48V 1MHz T riple Step-Down 10W 100mA White LED Driver (3.6V LEDs) Efficiency

3597 TA03

V OUT1 LED1 BIAS FAUL T PWM1-3 CTRL1-3 SYNC RT BOOST2 SW2 DA2 FB2 V OUT2 LED2 BOOST3 SW3 DA3 FB3 VOUT3 LED3 VREF TSET CTRLM L T3597 3.24k 100k 97k 91k 270k 2.2µF 0.1µF 10µF 100µH 0.1µF 2.2µF 100µH 3.24k 97k 0.1µF 2.2µF 100µH 3.24k 97k 100k 10k 82.5k VREF 49.9k 10µF VCC VIN 48V 33.2k ISET1 ISET2 ISET3 GND 20k 20k 20k VOUT1 VOUT2 VOUT3 LED CURRENT PER CHANNEL (mA) 0 10 EFFICIENCY (%) 60 50 80 7040 30 20

3597 TA03b

24V 200kHz T riple Step-Down 100mA RGB LED Driver Efficiency

3597 TA04

V OUT1 LED1 BIAS FAUL T PWM1-3 CTRL1-3 SYNC RT BOOST2 SW2 DA2 FB2 V OUT2 LED2 BOOST3 SW3 DA3 FB3 VOUT3 LED3 VREF TSET CTRLM L T3597 9.1k 100k 97k 15µF 0.22µF 10µF 470µH 0.22µF 15µF 470µH 9.1k 97k 0.22µF 15µF 470µH 9.1k 97k VREF 10µF 220k ISET1 ISET2 ISET3 GND 20k 20k 20k VIN 24V VOUT1 VOUT2 VOUT3 G B R LED CURRENT PER CHANNEL (mA) 0 10 EFFICIENCY (%) 60 50 80 7040 30 20

3597 TA04b

48V 1MHz T riple Step-Down 20mA RGB LED Driver

3597 TA05

V OUT1 LED1 BIAS FAUL T PWM1-3 CTRL1-3 SYNC RT BOOST2 SW2 DA2 FB2 V OUT2 LED2 BOOST3 SW3 DA3 FB3 VOUT3 LED3 VREF TSET CTRLM L T3597 9.1k 100k 97k 91k 270k 3.3µF 0.1µF 10µF 100µH 0.1µF 2.2µF 100µH 4.7k 97k 0.1µF 2.2µF 100µH 3.83k 97k 100k 10k 82.5k VREF 49.9k 10µF VCC VIN 48V 33.2k ISET1 ISET2 ISET3 GND 100k 100k 100k VOUT1 VOUT2 VOUT3 G B R

Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However , no responsibility is assumed for its use. Linear Technology Corporation makes no representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. PACKAGE DESCRIPTION Variation: UHG52 (39) 52-Lead Plastic QFN (5mm × 8mm) (Reference LTC DWG # 05-08-1846 Rev B) 5.00 ± 0.10 NOTE: 1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS PIN 1 TOP MARK (SEE NOTE 6) 51 50 48 4644 48 46 4451 50 18 19 20 21 22 23 24 25 26 BOTTOM VIEW—EXPOSED PAD 5.90 ±0.10

6.40 REF

8.00 ± 0.10 0.75 ± 0.05 0.75 ± 0.05 R = 0.10 TYP R = 0.10 TYP 0.20 ± 0.05 (UHG39) QFN 0410 REV B

0.40 BSC

0.80 BSC

0.70 TYP

0.60 TYP

0.200 REF

0.00 – 0.05 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPL Y SOLDER MASK TO AREAS THAT ARE NOT SOLDERED

3.20 REF

0.40 ±0.10 0.00 – 0.05 18 19 20 21 22 23 24 25 26 0.70 ± 0.05 41 39 37 35 34 33 32 31 30 29 28 27 17 16 15 14 13 12 11 9 7 6 4 2 0.40 BSC0.80 BSC 4.10 ± 0.05 5.50 ± 0.05 0.20 ± 0.05 5.90 ±0.05 2.90 ±0.05 7.10 ± 0.05 8.50 ± 0.05 PACKAGE OUTLINE 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.20mm 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 PIN 1 NOTCH R = 0.30 TYP OR 0.35 × 45° CHAMFER 2.90 ±0.10

Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear .com  LINEAR TECHNOLOGY CORPORATION 2011 LT 0311 • PRINTED IN USA RELATED PARTS TYPICAL APPLICATION PART NUMBER DESCRIPTION COMMENTS L T3476 Quad Output 1.5A, 2MHz High Current LED Driver with 1000:1 Dimming VIN: 2.8V to 16V , VOUT(MAX) = 36V , T rue Color PWM Dimming = 1000:1, ISD < 10µA, 5mm × 7mm QFN-10 Package L T3492 60V , 2.1MHz 3-Channel (ILED = 1A) Full Featured LED Driver VIN: 3V to 30V (40VMAX), VOUT(MAX) = 60V , T rue Color PWM Dimming = 3000:1, ISD < 1µA, 4mm × 5mm QFN-28 Package L T3496 45V , 2.1MHz 3-Channel (ILED = 1A) Full Featured LED Driver VIN: 3V to 30V (40VMAX), VOUT(MAX) = 45V , T rue Color PWM Dimming = 3000:1, ISD < 1µA, 4mm × 3mm QFN-28 Package L T3590 48V , 850kHz 50mA Buck Mode LED Driver VIN: 4.5V to 55V , T rue Color PWM Dimming = 200:1, ISD < 15µA, 2mm × 2mm DFN-6 and SC70 Packages L T3595 45V , 2.5MHz 16-Channel Full Featured LED Driver VIN: 4.5V to 55V , VOUT(MAX) = 45V T rue Color PWM Dimming = 5000:1, ISD < 1µA, 5mm × 9mm QFN-56 Package L T3596 60V , 1MHz 3-Channel Full Featured LED Driver VIN: 6V to 60V , VOUT(MAX) = 40V , T rue Color PWM Dimming = 10,000:1, ISD ≤ 2µA, 5mm × 8mm QFN-52 Package L T3598 44V , 1.5A, 2.5MHz Boost 6-Channel LED Driver VIN: 3V to 30V (40VMAX), VOUT(MAX) = 44V , T rue Color PWM Dimming = 1000:1, ISD < 1µA, 4mm × 4mm QFN-24 Package L T3599 2A Boost Converter with Internal 4-String 150mA LED Ballaster V IN: 3V to 30V , VOUT(MAX) = 44V , T rue Color PWM Dimming = 1000:1, ISD < 1µA, 5mm × 5mm QFN-32 and TSSOP-28 Packages L T3754 16-Channel x 50mA LED Driver with 60V Boost Controller and PWM Dimming V IN: 6V to 40V , VOUT(MAX) = 60V , T rue Color PWM Dimming = 3000:1, ISD < 2µA, 5mm × 5mm QFN-52 Package L T3760 8-Channel x 100mA LED Driver with 60V Boost Controller and PWM Dimming VIN: 6V to 40V , VOUT(MAX) = 60V , T rue Color PWM Dimming = 3000:1, ISD < 2µA, TSSOP-28 Package T riple Step-Down RGB Single Pixel LED Driver , 100mA Current 10,000:1 Dimming at 100Hz

3597 TA06

V OUT1 LED1 BIAS FAUL T PWM1:3 CTRL1:3 SYNC RT BOOST2 SW2 DA2 FB2 V OUT2 LED2 BOOST3 SW3 DA3 FB3 VOUT3 LED3 VREF TSET CTRLM L T3597 9.1k 100k 97k 91k 270k 3.3µF 0.1µF 10µF 100µH 0.1µF 3.3µF 100µH 9.1k 97k 0.1µF 3.3µF 100µH 9.1k 97k 100k 10k 82.5k VREF 49.9k 10µF VCC 10µF 33.2k ISET1 ISET2 ISET3 GND 20k 20k 20k VOUT1 VIN 48V VOUT2 VOUT3 R G B ILED 50mA/DIV PWM 2V/DIV

3597 TA06b