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The L T®3474/L T3474-1 are fi xed frequency step-down DC/DC converters designed to operate as constant-current sources. An internal sense resistor monitors the output current allowing accurate current regulation, ideal for driving high current LEDs. High output current accuracy is maintained over a wide current range, from 35mA to 1A, allowing a wide dimming range. Unique PWM circuitry allows a dimming range of 400:1, avoiding the color shift normally associated with LED current dimming. The high switching frequency offers several advantages, permitting the use of small inductors and ceramic capaci- tors. Small inductors combined with the 16-lead TSSOP surface mount package save space and cost versus alternative solutions. The constant switching frequency combined with low-impedance ceramic capacitors result in low, predictable output ripple. With their wide input range of 4V to 36V , the L T3474/ L T3474-1 regulate a broad array of power sources, from 5V logic rails to unregulated wall transformers, lead acid batteries and distributed power supplies. A current mode PWM architecture provides fast transient response and cycle-by-cycle current limiting. Frequency foldback and thermal shutdown provide additional protection. ■ Automotive and Avionic Lighting ■ Architectural Detail Lighting ■ Display Backlighting ■ Constant Current Sources n T rue Color PWM™ Delivers Constant Color with 400:1 Dimming Range n Wide Input Range: 4V to 36V n Up to 1A LED Current n Adjustable 200kHz–2MHz Switching Frequency n Adjustable Control of LED Current n Integrated Boost Diode n High Output Current Accuracy is Maintained Over a Wide Range from 35mA to 1A n Open LED (L T3474) and Short-Circuit Protection n High Side Sense Allows Grounded Cathode Connection n Uses Small Inductors and Ceramic Capacitors n L T3474-1 Drives LED Strings Up to 26V n Compact 16-Lead TSSOP Thermally Enhanced Surface Mount Package TYPICAL APPLICATION

DESCRIPTION

L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. True Color PWM is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. Patent Pending

FEATURES

APPLICATIONS

Effi ciency VIN BIAS OUT PWM LED LED1 DIMMING* CONTROL L T3474 0.1μF VIN 5V TO 36V 2.2μF 0.22μF 10μH

3474 TA01a

80.6k *SEE APPLICATIONS SECTION FOR DETAILS SHDN REF BOOST SW VADJ RT VC GND 2.2μF LED CURRENT (mA) EFFICIENCY (%)70 600 1000

3474 G02

VIN = 12V

PIN CONFIGURATION ABSOLUTE MAXIMUM RATINGS V Operating Temperature Range (Note 3) (Note 1) FE PACKAGE 16-LEAD PLASTIC TSSOP TOP VIEW DNC* OUT LED V IN SW BOOST BIAS GND DNC* GND PWM V ADJ VC REF SHDN R T θJC = 8°C/W , θJA = 40°C/W EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB *DO NOT CONNECT EXTERNAL CIRCUITRY TO THESE PINS. ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LT3474EFE#PBF LT3474EFE#TRPBF 3474EFE 16-Lead TSSOP –40°C to 85°C LT3474IFE#PBF LT3474IFE#TRPBF 3474IFE 16-Lead TSSOP –40°C to 125°C LT3474EFE-1#PBF LT3474EFE-1#TRPBF 3474EFE-1 16-Lead TSSOP –40°C to 85°C LT3474IFE-1#PBF LT3474IFE-1#TRPBF 3474IFE-1 16-Lead TSSOP –40°C to 125°C Consult LTC Marketing for parts specifi ed with wider operating temperature ranges. Consult LTC Marketing for information on non-standard lead based fi nish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifi cations, go to: http://www.linear.com/tapeandreel/ PARAMETER CONDITIONS MIN TYP MAX UNITS Minimum Input Voltage l 3.5 4 V Input Quiescent Current Not Switching 2.6 4 mA Shutdown Current SHDN = 0.3V, V BOOST = 0V, VOUT = 0V 0.01 2 μA LED Pin Current V ADJ Tied to VREF VADJ Tied to VREF/5 l l 0.98 0.968 0.193 0.186 0.2 1.02 1.025 0.207 0.210 A A A A REF Voltage l 1.23 1.25 1.265 V ELECTRICAL CHARACTERISTICS The l denotes the specifi cations which apply over the full operating temperature range, otherwise specifi cations are at TA = 25°C. VIN = 12V, VBOOST = 16V, VOUT = 4V unless otherwise noted (Note 3).

ELECTRICAL CHARACTERISTICS

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: This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed 125°C when overtemperature protection is active. Continuous operation above the specifi ed maximum operating junction temperature may impair device reliability. Note 3: The L T3474E and L T3474E-1 are guaranteed to meet performance specifi cations from 0°C to 70°C. Specifi cations over the –40°C to 85°C The l denotes the specifi cations which apply over the full operating temperature range, otherwise specifi cations are at TA = 25°C. VIN = 12V, VBOOST = 16V, VOUT = 4V unless otherwise noted (Note 3). PARAMETER CONDITIONS MIN TYP MAX UNITS Reference Voltage Line Regulation 5V < V IN < 36V 0.01 %/V Reference Voltage Load Regulation 0 < I REF < 250μA 0.0002 %/μA VADJ Pin Bias Current (Note 4) l 20 400 nA Switching Frequency R T = 80.6k l 470 450 500 530 540 kHz kHz Maximum Duty Cycle R T = 80.6k RT = 10k RT = 232k l 90 95 Foldback Frequency R T = 80.6k, VOUT = 0V 70 kHz SHDN Threshold (to Switch) 2.6 2.65 2.7 V SHDN Pin Current (Note 5) V SHDN = SHDN Threshold 8.3 10.3 12.3 μA PWM Threshold 0.4 0.9 1.2 V VC Switching Threshold 0.8 V VC Source Current V C = 1V 100 μA VC Sink Current V C = 1V 100 μA LED to VC Current Gain 1.5 μA/mA LED to VC Transresistance 1 V/mA VC to Switch Current Gain 2A / V VC Clamp Voltage 1.9 V VC Pin Current in PWM Mode V C = 1V, VPWM = 0.3V l 0.01 1 μA OUT Pin Clamp Voltage (LT3474) 13.2 13.8 14.5 V OUT Pin Current in PWM Mode V OUT = 4V, VPWM = 0.3V l 0.1 10 μA Switch Current Limit (Note 6) –40°C to 85°C LT3474I, LT3474I-1 at 125°C l 1.6 1.5 2.1 3.2 3.2 A A Switch VCESAT ISW = 1A 380 500 mV Boost Pin Current I SW = 1A 30 50 mA Switch Leakage Current 0.01 1 μA Minimum Boost Voltage (Note 7) 1.9 2.5 V Boost Diode Forward Voltage I DIO = 100mA 600 mV operating temperature range are assured by design, characterization and correlation with statistical process controls. The L T3474I and L T3474I-1 are guaranteed to meet performance specifi cations over the –40°C to 125°C operating temperature range. Note 4: Current fl ows out of pin. Note 5: Current fl ows into pin. Note 6: Current limit is guaranteed by design and/or correlation to static test. Slope compensation reduces current limit at higher duty cycles. Note 7: This is the minimum voltage across the boost capacitor needed to guarantee full saturation of the internal power switch.

TYPICAL PERFORMANCE CHARACTERISTICS Current Limit vs Duty Cycle Switch Current Limit vs Temperature Current Limit vs Output Voltage Oscillator Frequency vs TemperatureOscillator Frequency vs R T Oscillator Frequency Foldback LED Current vs V ADJ LED Current vs Temperature Switch Voltage Drop VADJ (V) LED CURRENT (mA) 600 800 1000

3474 GO3

0.25 0.5 0.75 1.25 TA = 25°C TEMPERATURE (°C) –50 LED CURRENT (mA) 800 1000 1200 25 75

3474 G04

–25 0 50 100 125 200 VADJ = VREF VADJ = VREF/5 SWITCH CURRENT (mA) 700 600 500 400 300 200 100

3474 G05

SWITCH VOL TAGE DROP (mV) TA = 25°C DUTY CYCLE (%) CURRENT LIMIT (A) 1.5 2.5

3474 G06

0.5 20 40 60 100 TYPICAL MINIMUM (125°C) MINIMUM (85°C) TEMPERATURE (°C) –50 –25 CURRENT LIMIT (A) 2.5 0 50 75

3474 G07

0.5 1.5 25 100 125 VOUT (V) CURRENT LIMIT (A) 0.5 1.5 2.5 2 468

3474 G08

TA = 25°C RT (kΩ) 100 OSCILLATOR FREQUENCY (kHz) 1000 100

3474 G09

TA = 25°C TEMPERATURE (°C) –50

400 OSCILLATOR FREQUENCY (kHz)

–25 0 25 50

3474 G10

RT = 80.6k VOUT (V) OSCILLATOR FREQUENCY (kHz)100 200 300 400 500 600 0.5 1 1.5 2

3474 G11

2.5 TA = 25°C RT = 80.6k

TYPICAL PERFORMANCE CHARACTERISTICS Schottky Reverse Leakage Schottky Forward Voltage Drop Open-Circuit Output Voltage and Input Current Minimum Input Voltage, One White Luxeon III Star Minimum Input Voltage, Two Series Connected White Luxeon III Stars Boost Pin Current Quiescent Current Reference Voltage TEMPERATURE (°C) –50 REVERSE CURRENT (μA)5 –25 0 25 50

3474 G15

VR = 5V VIN (V) OUTPUT VOLTAGE (V) INPUT CURRENT (mA) 10 20 30 40

3474 G16

TA = 25°C OUTPUT VOLTAGE INPUT CURRENT LT3474 LT3474-1 LT3474-1 LT3474 LED CURRENT (mA) VIN (V) 200 400 600 800

3474 G17

TA = 25°C TO START LED VOLTAGE TO RUN LED CURRENT (mA) VIN (V) 800

3474 G18

TA = 25°C TO START LED VOLTAGE FORWARD VOLTAGE (mV) FORWARD CURRENT (mA) 300 400 500 800

3474 G19

TA = 25°C SWITCH CURRENT (mA) BOOST PIN CURRENT (mA) 250 500 750 1000

3473 G12

TA = 25°C VIN (V) INPUT CURRENT (mA) 0.5 1.0 1.5 2.0 3.0 6 12 18 24

3474 G13

2.5 TA = 25°C TEMPERATURE (°C) –50 –25

1.235 VREF (V)

1.245 1.260 0 50 75

3474 G14

1.240 1.255 1.250 25 100 125

DNC (Pins 1, 16): Do not connect external circuitry to these pins, or tie them to GND. Leave the DNC pins fl oating. OUT (Pin 2): The OUT pin is the input to the current sense resistor . Connect this pin to the inductor and the output capacitor . LED (Pin 3): The LED pin is the output of the current sense resistor . Connect the anode of the LED here. V IN (Pin 4): The V IN pin supplies current to the internal circuitry and to the internal power switch and must be locally bypassed. SW (Pin 5): The SW pin is the output of the internal power switch. Connect this pin to the inductor and switching diode. BOOST (Pin 6): The BOOST pin is used to provide a drive voltage, higher than the input voltage, to the internal bipolar NPN power switch. BIAS (Pin 7): The BIAS pin connects through a Schottky diode to BOOST . Tie to OUT . GND (Pins 8, 15, Exposed Pad Pin 17): Ground. Tie both GND pins and the Exposed Pad directly to the ground plane. The Exposed Pad metal of the package provides both electrical contact to ground and good thermal contact to the printed circuit board. It must be soldered to the circuit board for proper operation. R T (Pin 9): The RT pin is used to set the internal oscilla- tor frequency. Tie an 80.6k resistor from RT to GND for a 500kHz switching frequency. SHDN (Pin 10): The SHDN pin is used to shut down the switching regulator and the internal bias circuits. The 2.6V switching threshold can function as an accurate under-voltage lockout. Pull below 0.3V to shut down the L T3474/L T3474-1. Pull above 2.65V to enable the L T3474/ L T3474-1. Tie to V IN if the SHDN function is unused. REF (Pin 11): The REF pin is the buffered output of the internal reference. Either tie the REF pin to the VADJ pin for a 1A output current, or use a resistor divider to generate a lower voltage at the V ADJ pin. Leave this pin unconnected if unused. VC (Pin 12): The Vc pin is the output of the internal error amp. The voltage on this pin controls the peak switch current. Use this pin to compensate the control loop. V ADJ (Pin 13): The V ADJ pin is the input to the internal voltage to current amplifi er . Connect the VADJ pin to the REF pin for a 1A output current. For lower output cur- rents, program the V ADJ pin using the following formula: ILED = 1A • VADJ/1.25V . PWM (Pin 14): The PWM pin controls the connection of the VC pin to the internal circuitry. When the PWM pin is low, the VC pin is disconnected from the internal circuitry and draws minimal current. If the PWM feature is unused, leave this pin unconnected.

Figure 1. Block Diagram

The L T3474 is a constant frequency, current mode regula- tor with an internal power switch capable of generating a constant 1A output. Operation can be best understood by referring to the Block Diagram. If the SHDN pin is tied to ground, the L T3474 is shut down and draws minimal current from the input source tied to V IN. If the SHDN pin exceeds 1.5V , the internal bias circuits turn on, including the internal regulator , reference, and oscillator . The switching regulator will only begin to operate when the SHDN pin exceeds 2.65V . The switcher is a current mode regulator . Instead of directly modulating the duty cycle of the power switch, the feedback loop controls the peak current in the switch during each cycle. Compared to voltage mode control, current mode control improves loop dynamics and provides cycle-by- cycle current limit. A pulse from the oscillator sets the RS fl ip-fl op and turns on the internal NPN bipolar power switch. Current in the switch and the external inductor begins to increase. When this current exceeds a level determined by the voltage at V C, current comparator C1 resets the fl ip-fl op, turning off the switch. The current in the inductor fl ows through the external Schottky diode and begins to decrease. The cycle begins again at the next pulse from the oscillator . In this way, the voltage on the V C pin controls the current through the inductor to the output. The internal error amplifi er regulates the output current by continually adjusting the V C pin voltage. The threshold for switching on the VC pin is 0.8V , and an active clamp of 1.9V limits the output current. The voltage on the VADJ pin sets the current through the LED pin. The NPN Q2 pulls a current proportional to the voltage on the V ADJ pin through the 100Ω resistor . The gm amplifi er servos the VC pin to set the current through the 0.1Ω resistor and the LED pin. When the voltage drop across the 0.1Ω resistor is equal to the voltage drop across the 100Ω resistor , the servo loop is balanced. Tying the REF pin to the VADJ pin sets the LED pin current to 1A. Tying a resistor divider to the REF pin allows the programming of LED pin currents of less than 1A. LED pin current can also be programmed by tying the V ADJ pin directly to a voltage source up to 1.25V . An LED can be dimmed with pulse width modulation us- ing the PWM pin and an external NFET . If the PWM pin is unconnected or pulled high, the part operates nominally. If the PWM pin is pulled low, the V C pin is disconnected from the internal circuitry and draws minimal current from the compensation capacitor . Circuitry drawing current from the OUT pin is also disabled. This way, the V C pin and the output capacitor store the state of the LED pin current until PWM is pulled high again. This leads to a highly linear relationship between pulse width and output light, allowing for a large and accurate dimming range. The R T pin allows programming of the switching frequency. For applications requiring the smallest external components possible, a fast switching frequency can be used. If very low or very high input voltages are required, a slower switching frequency can be programmed. During startup V OUT will be at a low voltage. The NPN Q2 can only operate correctly with suffi cient voltage at VOUT, around 1.7V . A comparator senses VOUT and forces the VC pin high until V OUT rises above 2V , and Q2 is operating correctly. The switching regulator performs frequency foldback dur- ing overload conditions. An amplifi er senses when VOUT is less than 2V and begins decreasing the oscillator frequency down from full frequency to 20% of the nominal frequency when V OUT = 0V . The OUT pin is less than 2V during startup, short circuit, and overload conditions. Frequency foldback helps limit switch current under these conditions.

where these problems might occur . prevent coupling problems from switching nodes.

3474 F03

Figure 3. Undervoltage LockoutFigure 2. External Overvoltage Protection

3474 F02

variety of switching frequencies. Table 1. Switching Frequencies losses and decreased effi ciency. increases as the switching frequency is decreased. and by the minimum duty cycle.

inductance is required to avoid sub-harmonic oscillations. the inductor value, and the input and output voltages. the series resistance (DCR) should be less than 0.2Ω. Table 2 lists several vendors and types that are suitable. Table 2. Inductors

To maintain output regulation, this peak current must be less than the L T3474’s switch current limit ILIM. For SW1, ILIM is at least 1.6A (1.5A at 125°C) at low duty cycles and decreases linearly to 1.15A (1.08A at 125°C) at DC = 0.8. The maximum output current is a function of the chosen inductor value: IOUT MAX() = ILIM – ΔIL Choosing an inductor value so that the ripple current is small will allow a maximum output current near the switch current limit. One approach to choosing the inductor is to start with the simple rule given above, look at the available inductors, and choose one to meet cost or space goals. Then use these equations to check that the L T3474 will be able to deliver the required output current. Note again that these equations assume that the inductor current is continuous. Discontinuous operation occurs when I OUT is less than ΔIL/2. Input Capacitor Selection Bypass the input of the L T3474 circuit with a 2.2μF or higher ceramic capacitor of X7R or X5R type. A lower value or a less expensive Y5V type will work if there is additional bypassing provided by bulk electrolytic capaci- tors or if the input source impedance is low. The following paragraphs describe the input capacitor considerations in more detail. Step-down regulators draw current from the input sup- ply in pulses with very fast rise and fall times. The input capacitor is required to reduce the resulting voltage ripple at the L T3474 input and to force this switching current into a tight local loop, minnimizing EMI. The input capacitor must have low impedance at the switching frequency to do this effectively, and it must have an adequate ripple current rating. The RMS input is: CI VV V V I INRMS OUT OUT IN OUT IN OUT= and is largest when VIN = 2VOUT (50% duty cycle). Con- sidering that the maximum load current is 1A, RMS ripple current will always be less than 0.5A The high switching frequency of the L T3474 reduces the energy storage requirements of the input capacitor , so that the capacitance required is less than 10μF . The combination of small size and low impedance (low equivalent series resistance or ESR) of ceramic capacitors makes them the preferred choice. The low ESR results in very low voltage ripple. Ceramic capacitors can handle larger magnitudes of ripple current than other capacitor types of the same value. Use X5R and X7R types. An alternative to a high value ceramic capacitor is a lower value ceramic along with a larger electrolytic capaci- tor . The electrolytic capacitor likely needs to be greater than 10μF in order to meet the ESR and ripple current requirements. The input capacitor is likely to see high surge currents when the input source is applied. Tanta- lum capacitors can fail due to an over-surge of current. Only use tantalum capacitors with the appropriate surge current rating. The manufacturer may also recommend operation below the rated voltage of the capacitor .

where ΔIL is the peak-to-peak ripple current in the inductor . with applied voltage and at temperature extremes. and X5R types. Table 3 lists several capacitor vendors. Table 3. Low-ESR Surface Mount Capacitors ceramic capacitor . For details, see Application Note 88. ripple and transient performance. the presence of output capacitor series resistance (ESR). and small circuit size, are therefore an option.

Peak reverse voltage is equal to the regulator input voltage. Table 4. Schottky Diodes

generate a voltage that is higher than the input voltage. the BOOST and SW pins is less than 25V . divider from the REF pin, as shown in Figure 5. Figure 4. Generating the Boost Voltage

3474 F04

Figure 5. Setting V ADJ with a Resistor Divider

3474 F04c

3474 F04b

3474 F04a

3474 F04d

not to exceed the 250μA current limit on the REF pin. pin and an external NFET tied to the cathode of the LED. ing off the LED and leaving the output capacitor charged. dimming ratio and the current dimming ratio.

3474 F05

Figure 6. Dimming with an NFET and Resistor Divider

3474 F06

Figure 7. Dimming Using PWM Signal

the overall voltage above 2.4V . Figure 8. Recommended Component Placement

0.1μF VIN 12V TO 36V 2.2μF 10V LED CURRENT 0.22μF 10V 10μH

3474 TA02

33.2k SHDN REF BOOST SW VADJ RT VC GND 2.2μF 50V LED2 D1: MBRM 140 C1 TO C3: X5R OR X7R LED CURRENT (mA) EFFICIENCY (%)70 600 1000

3474 G01

VIN = 12V VIN = 24V VIN BIAS OUT PWM LED LED1 D1L T3474 3.3nF VIN 6V TO 36V 2.2μF 6.3V 0.22μF 6.3V 10μH

3474 TA01

80.6k 10k 0.1μF PWM SHDN REF BOOST SW VADJ RT VC GND 2.2μF 50V D1: B140HB C1 TO C3: X5R OR X7R M1: Si2302ADS ILED1 500mA/DIV V(PWM) 5V/DIV 1ms/DIV Effi ciency, Two LED Output LED Current in PWM ModeStep-Down 1A LED Driver with PWM Dimming Step-Down 1A LED Driver with Two Series Connected LED Output TYPICAL APPLICATIONS

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 16-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1663) Exposed Pad Variation BA FE16 (BA) TSSOP 0204 0.09 – 0.20 (.0035 – .0079) 0° – 8° 0.25 REF 0.50 – 0.75 (.020 – .030) 4.30 – 4.50* (.169 – .177) 13 4 5 6 7 8 10 9 4.90 – 5.10* (.193 – .201) 16 1514 13 12 11 1.10 (.0433) MAX 0.05 – 0.15 (.002 – .006) 0.65 (.0256) BSC 2.74 (.108) 2.74 (.108) 0.195 – 0.30 (.0077 – .0118) TYP MILLIMETERS (INCHES) *DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.150mm (.006") PER SIDE NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS 2. DIMENSIONS ARE IN RECOMMENDED SOLDER PAD LAYOUT 3. DRAWING NOT TO SCALE 0.45 ±0.05

0.65 BSC

4.50 ±0.10 6.60 ±0.10 1.05 ±0.10 2.74 (.108) 2.74 (.108) SEE NOTE 4 4. RECOMMENDED MINIMUM PCB METAL SIZE FOR EXPOSED PAD ATTACHMENT 6.40 (.252) BSC

Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear .com © LINEAR TECHNOLOGY CORPORATION 2005 LT 1008 REV D • PRINTED IN USA RELATED PARTS TYPICAL APPLICATION PART NUMBER DESCRIPTION COMMENTS LT1618 Constant Current, 1.4MHz, 1.5A Boost Converter V IN: 1.6V to 18V, VOUT(MAX) = 36V, IQ = 1.8mA, ISD = <1μA, LT1766 60V, 1.2A (I OUT), 200kHz, High Effi ciency Step-Down DC/DC Converter V IN: 5.5V to 60V, VOUT(MAX) = 1.20V, IQ = 2.5mA, ISD = 25μA, TSSOP16/E Packages LT1956 60V, 1.2A (I OUT), 500kHz, High Effi ciency Step-Down DC/DC Converter V IN: 5.5V to 60V, VOUT(MAX) = 1.20V, IQ = 2.5mA, ISD = 25μA, TSSOP16/E Packages LT1961 1.5A (I SW), 1.25MHz, High Effi ciency Step-Up DC/DC Converter V IN: 3V to 25V, VOUT(MAX) = 35V, IQ = 0.9mA, ISD = 6μA, LT1976/LT1977 60V, 1.2A (I OUT), 200kHz/500kHz, High Effi ciency Step-Down DC/DC Converters with BurstMode ® Operation VIN: 3.3V to 60V, VOUT(MAX) = 1.20V, IQ = 100μA, ISD = <1μA, LT3430/LT3431 60V, 2.5A (I OUT), 200kHz, High Effi ciency Step-Down DC/DC Converters V IN: 5.5V to 60V, VOUT(MAX) = 1.20V, IQ = 2.5μA, ISD = <25μA, TSSOP16/E Packages LT3433 60V, 400mA (I OUT), 200kHz, High Effi ciency Step-Up/Step-Down DC/DC Converters with Burst Mode Operation VIN: 4V to 60V, VOUT: 3.3V to 20V, IQ = 100μA, ISD = <1μA, TSSOP16E Package LT3434/LT3435 60V, 2.5A (I OUT), 200kHz/500kHz, High Effi ciency Step-Down DC/DC Converters with Burst Mode Operation VIN: 3.3V to 60V, VOUT(MAX) = 1.20V, IQ = 100μA, ISD = <1μA, LTC3453 1MHz, 800mA Synchronous Buck-Boost High Power LED Driver V IN: 2.7V to 5.5V, VOUT(MAX) = 5.5V, IQ = 2.5mA, ISD = <6μA, LT3467/LT3467A 1.1A (I SW), 1.3MHz/2.1MHz, High Effi ciency Step-Up DC/DC Converters with Integrated Soft-Start VIN: 2.4V to 16V, VOUT(MAX) = 40V, IQ = 1.2mA, ISD = <1μA, ThinSOT™ Package LT3477 3A, 42V, 3MHz Step-Up Regulator with Dual Rail to Rail Current Sense V IN: 2.5V to 2.5V, VOUT(MAX) = 40V, IQ = 5mA, ISD = <1μA, QFN, TSSOP16E Packages LT3479 3A, Full Featured DC/DC Converter with Soft-Start and Inrush Current Protection VIN: 2.5V to 24V, VOUT(MAX) = 40V, IQ = 6.5mA, ISD = <1μA, DFN and TSSOP Packages Burst Mode is a registered trademark of Linear Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation. VIN BIAS OUT LED PWM L T3474-1 0.1μF VIN 21V TO 36V 2.2μF 25V R2 10k 100k1A LED CURRENT fSW = 500kHz 12V TO 18V LED VOL TAGE 0.22μF 16V 47μH

3474 TA02a

80.6k SHDN REF BOOST SW VADJ RT VC GND 2.2μF 50V D1: MBRM 140 D2: 7.5V Zener Diode D3: 22V Zener Diode Q1: MMBT3904 C1 TO C3: X5R OR X7R Step-Down 1A LED Driver with Four Series Connected LED Output