LT3491 White LED Driver with Integrated Schottky in SC70 and 2mm × 2mm DFN DESCRIPTIO U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Drives Up to Six White LEDs from a 3V Supply High Side Sense Allows “One Wire Current Source” Internal Schottky Diode One Pin Dimming and Shutdown 27V Open LED Protection 2.3MHz Switching Frequency ±5% Reference Accuracy VIN Range: 2.5V to 12V Requires Only 1µF Output Capacitor Wide 300:1 True Color PWMTM Dimming Range 8-Lead SC70 Package Low Profile 6-Lead DFN Package (2mm × 2mm × 0.75mm) U APPLICATIO S ■ ■ ■ ■ Cellular Phones PDAs, Handheld Computers Digital Cameras MP3 Players GPS Receivers The 2.3MHz switching frequency allows the use of tiny inductors and capacitors. A single pin performs both shutdown and accurate LED dimming control. Few external components are needed: open-LED protection and the Schottky diode are all contained inside the tiny SC70 and 2mm × 2mm DFN packages. With such a high level of integration, the LT3491 provides a high efficiency LED driver solution in the smallest of spaces. , LTC, LT and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. U ■ The LT®3491 is a fixed frequency step-up DC/DC converter specifically designed to drive up to six white LEDs in series from a Li-Ion cell. Series connection of the LEDs provides identical LED currents resulting in uniform brightness and eliminating the need for ballast resistors. The device features a unique high side LED current sense that enables the part to function as a “one wire current source;” one side of the LED string can be returned to ground anywhere, allowing a simpler one wire LED connection. Traditional LED drivers use a grounded resistor to sense LED current, requiring a 2-wire connection to the LED string. TYPICAL APPLICATIO Efficiency Li-Ion Driver for Four White LEDs SHUTDOWN AND DIMMING CONTROL 80 VIN = 3.6V 4 LEDs 75 CTRL VIN L1 10µH 70 CAP RSENSE 10Ω LT3491 SW LED GND C2 1µF C1 1µF EFFICIENCY (%) VIN 3V TO 5V 65 60 55 50 45 40 0 3491 TA01a C1: TAIYO YUDEN LMK212BJ105MD C2: TAIYO YUDEN GMK316BJ105ML L1: MURATA LQH32CN100 5 10 15 20 LED CURRENT (mA) 3491 TA01b 3491fa 1 LT3491 W W W AXI U U ABSOLUTE RATI GS (Note 1) Input Voltage (VIN) ................................................. SW Voltage ............................................................. CAP Voltage ............................................................ CTRL Voltage .......................................................... 12V 32V 32V 12V LED Voltage ............................................................ 32V Operating Temperature Range (Note 2) .. – 40°C to 85°C Maximum Junction Temperature ......................... 125°C Storage Temperature Range ................ – 65°C to 150°C Lead Temperature (Soldering, 10sec, SC-70) ......... 300°C U U W PACKAGE/ORDER I FOR ATIO TOP VIEW TOP VIEW 6 CTRL VIN 1 GND 2 7 SW 3 8 CAP 7 LED 6 CTRL 5 VIN SW 1 GND 2 GND 3 GND 4 5 LED 4 CAP SC8 PACKAGE 8-LEAD PLASTIC SC70 DC PACKAGE 6-LEAD (2mm × 2mm) PLASTIC DFN TJMAX = 125°C, θJA = 270°C/ W TJMAX = 125°C, θJA = 102°C/W, θJC = 20°C/ W EXPOSED PAD (PIN 7) SHOULD BE CONNECTED TO PCB GROUND ORDER PART NUMBER DC PART MARKING ORDER PART NUMBER DC PART MARKING LT3491EDC LCHJ LT3491ESC8 LBXQ Order Options Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF Lead Free Part Marking: http://www.linear.com/leadfree/ Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C. VIN = 3V, VCTRL = 3V, unless otherwise specified. PARAMETER CONDITIONS MIN Minimum Operating Voltage TYP MAX UNITS 200 210 mV 2.5 LED Current Sense Voltage (VCAP – VLED) VCAP = 30V CAP, LED Pin Bias Current VCAP = 16V, VLED = 16V ● 190 V 40 µA 2.5 V 2.6 8 4 10 mA µA 2.8 MHz 20 VCAP, VLED Common Mode Minimum Voltage Supply Current VCAP = 16V, VLED = 15V, CTRL = 3V CTRL = 0V Switching Frequency 1.8 2.3 Maximum Duty Cycle ● 88 92 % Switch Current Limit ● 260 350 mA Switch VCESAT ISW = 200mA 200 Switch Leakage Current VSW = 16V 0.1 VCTRL for Full LED Current VCAP = 30V ● ● µA 50 mV 1.5 V VCTRL to Shut Down IC VCTRL to Turn On IC mV 5 100 CTRL Pin Bias Current mV 100 ● CAP Pin Overvoltage Protection Schottky Forward Drop ISCHOTTKY = 100mA Schottky Leakage Current VR = 20V 26 27 nA 28 V 4 µA 0.8 V 3491fa 2 LT3491 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: The LT3491E is guaranteed to meet performance specifications from 0°C to 85°C. Specifications over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls. U W TYPICAL PERFOR A CE CHARACTERISTICS (TA = 25°C unless otherwise specified) Switch Saturation Voltage (VCESAT) 250 200 150 100 50 0 0 50 350 300 250 200 150 100 200 400 800 1000 600 SCHOTTKY FORWARD DROP (mV) 160 120 80 40 0 3 6 9 3491 G03 Input Current in Output Open Circuit 6 5 29 28 27 26 25 2000 4 3 2 1 0 3 0 6 9 12 0 VIN (V) VCTRL (mV) 3 6 VIN (V) 9 12 3491 G06 3491 G05 3491 G04 Transient Response Switching Waveform VSW 10V/DIV VCAP 5V/DIV VCAP 50mV/DIV VCTRL 5V/DIV IL 100mA/DIV IL 200mA/DIV VIN = 3.6V 200ns/DIV FRONT PAGE APPLICATION CIRCUIT 12 VIN (V) INPUT CURRENT (mA) OUTPUT CLAMP VOLTAGE (V) 200 SENSE VOLTAGE (mV) 1200 30 1500 3 Open-Circuit Output Clamp Voltage 240 1000 6 3491 G02 Sense Voltage (VCAP – VLED) vs VCTRL 500 9 0 0 3491 G01 0 12 50 0 100 150 200 250 300 350 400 SWITCH CURRENT (mA) SHUTDOWN CURRENT (µA) SCHOTTKY FORWARD CURRET (mA) SWITCH SATURATION VOLTAGE (mV) 15 400 300 0 Shutdown Current (VCTRL = 0V) Schottky Forward Voltage Drop 350 3491 G07 VIN = 3.6V 1ms/DIV FRONT PAGE APPLICATION CIRCUIT 3491 G08 3491fa 3 LT3491 U W TYPICAL PERFOR A CE CHARACTERISTICS (TA = 25°C unless otherwise specified) Switching Current Limt vs Duty Cycle Quiescent Current (VCTRL = 3V) 3.0 15 450 400 SCHOTTKY LEAKAGE CURRENT (µA) 25°C 2.5 350 CURRENT LIMIT (mA) QUIESCENT CURRENT (mA) Schottky Leakage Current vs Temperature 2.0 1.5 1.0 300 250 200 150 100 0.5 50 0 0 3 6 VIN (V) 9 30 50 60 70 DUTY CYCLE (%) 40 3491 G09 100 4 3 2 0 –50 –25 125 50 25 75 0 TEMPERATURE (°C) 100 3491 G12 120 80 –50°C 25°C 85°C 0 0 500 1000 VCTRL (mV) 1500 2.05 2.00 1.95 –50 125 2000 50 25 0 75 TEMPERATURE (°C) 100 212 212 208 208 204 200 204 200 196 196 192 125 Sense Voltage (VCAP – VLED) vs Temperature 5 10 15 20 25 VCAP (V) 3491 G15 –25 3419 G14 SENSE VOLTAGE (mV) SENSE VOLTAGE (mV) 200 40 2.10 Sense Voltage (VCAP – VLED) vs VCAP 240 100 2.15 3491 G13 Sense Voltage (VCAP – VLED) vs VCTRL 160 75 Switching Frequency vs Temperature 1 50 25 0 75 TEMPERATURE (°C) 0 25 50 TEMPERATURE (°C) 3491 G11 SWITCH FREQUENCY (MHz) INPUT CURRENT (mA) OUTPUT CLAMP VOLTAGE (V) 26 –25 –25 VIN = 3V 5 29 25 –50 3 2.20 6 27 6 Input Current in Output Open Circuit vs Temperature 30 28 9 3491 G10 Open-Circuit Output Clamp Voltage vs Temperature SENSE VOLTAGE (mV) 90 80 12 0 –50 0 12 VR = 10V VR = 16V VR = 20V 3491 G16 192 –50 –25 50 25 0 75 TEMPERATURE (°C) 100 125 3491 G17 3491fa 4 LT3491 U U U PI FU CTIO S (SC70/DFN) SW (Pin 1/Pin 3): Switch Pin. Minimize trace area at this pin to minimize EMI. Connect the inductor at this pin. GND (Pins 2, 3, 4/Pin 2): Ground Pins. All three pins should be tied directly to local ground plane. VIN (Pin 5/Pin 1): Input Supply Pin. Must be locally bypassed. CTRL (Pin 6/Pin 6): Dimming and Shutdown Pin. Connect this pin below 50mV to disable the driver. As the pin voltage is ramped from 0V to 1.5V, the LED current ramps from 0 to ILED ( = 200mV/RSENSE). The CTRL pin must not be left floating. LED (Pin 7/Pin 5): Connection Point for the Anode of the First LED and the Sense Resistor. The LED current can be programmed by : ILED = 200mV RSENSE CAP (Pin 8/Pin 4): Output of the Driver. This pin is connected to the cathode of internal Schottky. Connect the output capacitor to this pin and the sense resistor from this pin to the LED pin. EXPOSED PAD (NA/Pin 7): The Exposed Pad should be soldered to the PCB ground to achieve the rated thermal performance. W BLOCK DIAGRA 5 1 VIN SW PWM COMP – CAP 8 DRIVER A2 R + S Q1 Q OVERVOLTAGE PROTECTION + Σ R A3 – RAMP GENERATOR + OSCILLATOR A1 RC START-UP CONTROL + + – VREF 1.25V SHDN A = 6.25 – LED 7 CC CTRL 6 PIN NUMBERS CORRESPOND TO THE 8-PIN SC70 PACKAGE GND PINS 2, 3, 4 3491 F01 Figure 1. Block Diagram 3491fa 5 LT3491 U OPERATIO The LT3491 uses a constant frequency, current mode control scheme to provide excellent line and load regulation. Operation can be best understood by referring to the Block Diagram in Figure 1. At power up, the capacitor at the CAP pin is charged up to VIN (input supply voltage) through the inductor and the internal Schottky diode. If CTRL is pulled higher than 100mV, the bandgap reference, the start-up bias and the oscillator are turned on. At the start of each oscillator cycle, the power switch Q1 is turned on. 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, A2. When this voltage exceeds the level at the negative input of A2, the PWM logic turns off the power switch. The level at the negative input of A2 is set by the error amplifier A1, and is simply an amplified version of the difference between the VCAP and VLED voltage and the bandgap reference. In this manner the error amplifier, A1, sets the correct peak current level in inductor L1 to keep the output in regulation. The CTRL pin is used to adjust the LED current. The LT3491 enters into shutdown when CTRL is pulled lower than 50mV. Minimum Output Current The LT3491 can drive a 3-LED string at 2mA LED current without pulse skipping using the same external components shown in the application circuit on the front page of this data sheet. As current is further reduced, the device will begin skipping pulses. This will result in some low frequency ripple, although the average LED current remains regulated down to zero. The photo in Figure 2 details circuit operation driving three white LEDs at 2mA load. Peak inductor current is less than 60mA and the regulator operates in discontinuous mode, meaning the inductor current reaches zero during the discharge phase. After the inductor current reaches zero, the SW pin exhibits ringing due to the LC tank circuit formed by the inductor in combination with the switch and the diode capacitance. This ringing is not harmful; far less spectral energy is contained in the ringing than in the switch transitions. IL 50mA/DIV VSW 10V/DIV VIN = 4.2V ILED = 2mA 3 LEDs 200ns/DIV 3491 F02 Figure 2. Switching Waveforms 3491fa 6 LT3491 U W U U APPLICATIO S I FOR ATIO INDUCTOR SELECTION A 10µH inductor is recommended for most LT3491 applications. Although small size and high efficiency are major concerns, the inductor should have low core losses at 2.3MHz and low DCR (copper wire resistance). Some small inductors in this category are listed in Table 1. The efficiency comparison of different inductors is shown in Figure 3. Table 2 shows a list of several ceramic capacitor manufacturers. Consult the manufacturers for detailed information on their entire selection of ceramic parts. Table 2. Recommended Ceramic Capacitor Manufacturers Taiyo Yuden (800) 368-2496 www.t-yuden.com AVX (803) 448-9411 www.avxcorp.com Murata (714) 852-2001 www.murata.com Table 1. Recommended Inductors L (µH) DCR (Ω) CURRENT RATING (mA) LQH32CN100K53 LQH2MCN100K02 10 10 0.3 1.2 450 225 Murata www.murata.com SD3112-100 10 0.446 550 Cooper www.cooperet.com 1001AS-100M (TYPE D312C) 10 0.48 460 Toko www.toko.com CDRH2D11 CDRH2D14 10 10 0.5375 0.294 280 700 Sumida www.sumida.com PART VENDOR 80 OVERVOLTAGE PROTECTION The LT3491 has an internal open-circuit protection circuit. In the cases of output open circuit, when the LEDs are disconnected from the circuit or the LEDs fail open circuit, VCAP is clamped at 27V (typ). The LT3491 will then switch at a very low frequency to minimize input current. The VCAP and input current during output open circuit are shown in the Typical Performance Characteristics. Figure 4 shows the transient response when the LEDs are disconnected. 75 EFFICIENCY (%) 70 IL 200mA/DIV 65 60 VIN = 3.6V 4 LEDs FRONT PAGE APPLICATION CIRCUIT MURATA LQH2MCN100K02 MURATA LQH32CN100K53 TOKO 10001AS-100M SUMIDA CDRH2D11 SUMIDA CDRH2D14 55 50 45 40 35 30 0 5 10 15 LED CURRENT (mA) VCAP 10V/DIV 20 3491 F03 VIN = 3.6V CIRCUIT OF FRONT PAGE APPLICATION 500µs/DIV 3491 F04 LEDs DISCONNECTED AT THIS INSTANT Figure 4. Output Open-Circuit Waveform Figure 3. Efficiency Comparison of Different Inductors CAPACITOR SELECTION INRUSH CURRENT The small size of ceramic capacitors make them ideal for LT3491 applications. Use only X5R and X7R types because they retain their capacitance over wider temperature ranges than other types such as Y5V or Z5U. A 1µF input capacitor and a 1µF output capacitor are sufficient for most applications. The LT3491 has a built-in Schottky diode. When supply voltage is applied to the VIN pin, an inrush current flows through the inductor and the Schottky diode and charges up the CAP voltage. The Schottky diode inside the LT3491 can sustain a maximum current of 1A. 3491fa 7 LT3491 U W U U APPLICATIO S I FOR ATIO For low DCR inductors, which is usually the case for this application, the peak inrush current can be simplified as follows: IPK = α= ILED (mA) VIN – 0.6 ⎛ α π⎞ • exp ⎜ – • ⎟ ⎝ ω 2⎠ L•ω r 2 •L ω= Table 4. RSENSE Value Selection for 200mV Sense 5 40 10 20 15 13.3 20 10 DIMMING CONTROL There are three different types of dimming control circuits. The LED current can be set by modulating the CTRL pin with a DC voltage, a filtered PWM signal or directly with a PWM signal. 1 r2 – L • C 4 • L2 where L is the inductance, r is the DCR of the inductor and C is the output capacitance. Table 3 gives inrush peak currents for some component selections. Table 3. Inrush Peak Currents VIN (V) r (Ω) L (µH) COUT (µF) IP (A) 4.2 0.3 10 1.0 1.06 4.2 1.2 10 1.0 0.86 4.2 0.58 15 1.0 0.83 4.2 1.6 15 1.0 0.68 PROGRAMMING LED CURRENT The feedback resistor (RSENSE) and the sense voltage (VCAP – VLED) control the LED current. The CTRL pin controls the sense reference voltage as shown in the Typical Performance Characteristics. For CTRL higher than 1.5V, the sense reference is 200mV, which results in full LED current. In order to have accurate LED current, precision resistors are preferred (1% is recommended). The formula and table for RSENSE selection are shown below. RSENSE = RSENSE (Ω) Using a DC Voltage For some applications, the preferred method of brightness control is a variable DC voltage to adjust the LED current. The CTRL pin voltage can be modulated to set the dimming of the LED string. As the voltage on the CTRL pin increases from 0V to 1.5V, the LED current increases from 0 to ILED. As the CTRL pin voltage increases beyond 1.5V, it has no effect on the LED current. The LED current can be set by: ILED ≈ 200mV , when VCTRL > 1.5V RSENSE ILED ≈ VCTRL , when VCTRL < 1.25V 6.225 • RSENSE Feedback voltage variation versus control voltage is given in the Typical Performance Characteristics. 200mV ILED 3491fa 8 LT3491 U W U U APPLICATIO S I FOR ATIO Using a Filtered PWM Signal A filtered PWM signal can be used to control the brightness of the LED string. The PWM signal is filtered (Figure 5) by a RC network and fed to the CTRL pin. The corner frequency of R1, C1 should be much lower than the frequency of the PWM signal. R1 needs to be much smaller than the internal impedance of the CTRL pin which is 10MΩ (typ). PWM 10kHz TYP LT3491 R1 100k C1 0.1µF CTRL level Si2302 MOSFET can be used since its source is connected to ground. The PWM signal is applied to the CTRL pin of the LT3491 and the gate of the MOSFET. The PWM signal should traverse between 0V to 2.5V, to ensure proper turn on and off of the driver and the NMOS transistor Q1. When the PWM signal goes high, the LEDs are connected to ground and a current of ILED = 200mV/ RSENSE flows through the LEDs. When the PWM signal goes low, the LEDs are disconnected and turn off. The MOSFET ensures that the LEDs quickly turn off without discharging the output capacitor which in turn allows the LEDs to turn on faster. Figure 7 shows the PWM dimming waveforms for the circuit in Figure 6. 3491 F05 VIN 3V TO 5V L1 10µH Figure 5. Dimming Control Using a Filtered PWM Signal VIN SW Direct PWM Dimming Changing the forward current flowing in the LEDs not only changes the intensity of the LEDs, it also changes the color. The chromaticity of the LEDs changes with the change in forward current. Many applications cannot tolerate any shift in the color of the LEDs. Controlling the intensity of the LEDs with a direct PWM signal allows dimming of the LEDs without changing the color. In addition, direct PWM dimming offers a wider dimming range to the user. Dimming the LEDs via a PWM signal essentially involves turning the LEDs on and off at the PWM frequency. The typical human eye has a limit of ~60 frames per second. By increasing the PWM frequency to ~80Hz or higher, the eye will interpret that the pulsed light source is continuously on. Additionally, by modulating the duty cycle (amount of “ontime”), the intensity of the LEDs can be controlled. The color of the LEDs remains unchanged in this scheme since the LED current value is either zero or a constant value. Figure 6 shows a Li-Ion powered driver for four white LEDs. Direct PWM dimming method requires an external NMOS tied between the cathode of the lowest LED in the string and ground as shown in Figure 6. A simple logic CAP C1 1µF RSENSE 10Ω LT3491 LED GND CTRL 2.5V 0V C2 1µF PWM FREQ Q1 Si2302 100k 3491 F06 Figure 6. Li-Ion to Four White LEDs with Direct PWM Dimming ILED 20mA/DIV IL 200mA/DIV PWM 5V/DIV VIN = 3V 4 LEDs 2ms/DIV 3491 F07 Figure 7. Direct PWM Dimming Waveforms 3491fa 9 LT3491 U W U U APPLICATIO S I FOR ATIO The time it takes for the LED current to reach its programmed value sets the achievable dimming range for a given PWM frequency. For example, the settling time of the LED current in Figure 7 is approximately 30µs for a 3V input voltage. The achievable dimming range for this application and 100Hz PWM frequency can be determined using the following method. Example: down to 100mV. The use of both techniques together allows the average LED current for the four LED application to be varied from 20mA down to less than 20µA. Figure 9 shows the application for dimming using both analog dimming and PWM dimming. A potentiometer must be added to ensure that the gate of the NMOS receives a logic-level signal, while the CTRL signal can be adjusted to lower amplitudes. ƒ = 100Hz, t SETTLE = 30µs tPERIOD = 1 1 = = 0.01s ƒ 100 100Hz 1kHz t 0.01s Dim Range = PERIOD = = 300 : 1 t SETTLE 30µs Min Duty Cycle = 10kHz t SETTLE 30µs • 100 = • 10 00 = 0.3% tPERIOD 0.01s 1 10 The dimming range can be further extended by changing the amplitude of the PWM signal. The height of the PWM signal sets the commanded sense voltage across the sense resistor through the CTRL pin. In this manner both analog dimming and direct PWM dimming extend the dimming range for a given application. The color of the LEDs no longer remains constant because the forward current of the LED changes with the height of the CTRL signal. For the four LED application described above, the LEDs can be dimmed first, modulating the duty cycle of the PWM signal. Once the minimum duty cycle is reached, the height of the PWM signal can be decreased below 1.5V 1000 PWM DIMMING RANGE Duty Cycle Range = 100% → 0.3% at 100Hz The calculations show that for a 100Hz signal the dimming range is 300 to 1. In addition, the minimum PWM duty cycle of 0.3% ensures that the LED current has enough time to settle to its final value. Figure 8 shows the dimming range achievable for three different frequencies with a settling time of 30µs. 100 3491 F08 Figure 8. Dimming Range Comparison of Three PWM Frequencies VIN 3V TO 5V L1 10µH VIN SW C1 1µF CAP RSENSE 10Ω LT3491 LED GND CTRL C2 1µF 2.5V PWM FREQ 0V Q1 Si2302 100k 3491 F09 Figure 9. Li-Ion to Four White LEDs with Both PWM Dimming and Analog Dimming 3491fa 10 LT3491 U W U U APPLICATIO S I FOR ATIO LOW INPUT VOLTAGE APPLICATIONS BOARD LAYOUT CONSIDERATIONS The LT3491 can be used in low input voltage applications. The input supply voltage to the LT3491 must be 2.5V or higher. However, the inductor can be run off a lower battery voltage. This technique allows the LEDs to be powered off two alkaline cells. Most portable devices have a 3.3V logic supply voltage which can be used to power the LT3491. The LEDs can be driven straight from the battery, resulting in higher efficiency. 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 essential. Minimize the length and area of all traces connected to the switching node pin (SW). Keep the sense voltage pins (CAP and LED) away from the switching node. Place COUT next to the CAP pin. Always use a ground plane under the switching regulator to minimize interplane coupling. Recommended component placement is shown in Figure 11. Figure 10 shows three LEDs powered by two AA cells. The battery is connected to the inductor and the chip is powered off a 3.3V logic supply voltage. SHUTDOWN AND DIMMING CONTROL 3.3V CTRL C1 0.1µF 2 AA CELLS 2V TO 3.2V VIN L1 10µH CAP RSENSE 10Ω LT3491 SW LED C2 2.2µF GND C1 1µF 3491 F10 C1: TAIYO YUDEN LMK212BJ105MD C2: TAIYO YUDEN GMK325BJ225ML L1: MURATA LQH32CN100 Figure 10. 2 AA Cells to Three White LEDs CIN CTRL LED RSENSE VIN GND 5 4 6 3 7 2 CIN VIN CTRL L1 1 1 8 2 SW COUT 6 L1 3 GND 7 5 LED 4 CAP SW CAP COUT RSENSE GND 3491 F11 (A) SC70 PACKAGE (B) DFN PACKAGE Figure 11. Recommended Component Placement 3491fa 11 LT3491 U TYPICAL APPLICATIO S Li-Ion Driver for One White LED Efficiency 60 C2 1µF 50 EFFICIENCY (%) RSENSE 10Ω LED VIN 3V TO 5V CAP VIN L1 10µH SW 45 40 35 30 25 LT3491 C1 1µF VIN = 3.6V 55 SHUTDOWN AND DIMMING CONTROL CTRL GND 20 15 10 3491 TA07a 5 0 C1: TAIYO YUDEN LMK212BJ105MD C2: TAIYO YUDEN GMK316BJ105ML L1: MURATA LQH32CN100 3491 TA07b Li-Ion Driver for Two White LEDs Efficiency 70 C2 1µF EFFICIENCY (%) 60 LED CAP VIN L1 10µH LT3491 SW C1 1µF VIN = 3.6V 65 RSENSE 10Ω VIN 3V TO 5V 20 10 15 LED CURRENT (mA) SHUTDOWN AND DIMMING CONTROL CTRL GND 55 50 45 40 35 30 25 3491 TA08a 0 10 5 20 15 LED CURRENT (mA) C1: TAIYO YUDEN LMK212BJ105MD C2: TAIYO YUDEN GMK316BJ105ML L1: MURATA LQH32CN100 3491 TA08b Efficiency 2-Cell Li-Ion Driver for Torch and Flash Mode LED Control 80 C2 4.7µF VIN 6V TO 9V 75 D1 FLASH MODE ILED = 200mA V CTRL 1.5V LED L1 10µH VIN C1 1µF 70 65 60 LT3491 CTRL VCTRL 680mV TORCH MODE ILED = 100mA EFFICIENCY (%) RSENSE 1Ω CAP ILED = 100mA SW 55 GND 3491 TA09a C1: TAIYO YUDEN LMK212BJ105MD C2: TAIYO YUDEN LMK212BJ475MG D1: AOT-2015 HPW1751B L1: MURATA LQH32CN100 50 6 6.5 7 7.5 VIN (V) 8 8.5 9 3491 TA09b 3491fa 12 LT3491 U TYPICAL APPLICATIO S 12V to One White LED at 200mA Efficiency C2 4.7µF 75 RSENSE 1Ω C3 1µF EFFICIENCY (%) PVIN 12V 80 D1 CAP VIN 3V LED L1 15µH VIN SHUTDOWN AND DIMMING CONTROL C1 1µF LT3491 70 65 60 SW 55 3491 TA02a 50 CTRL GND 0 C1, C3: TAIYO YUDEN LMK212BJ105MD C2: TAIYO YUDEN LMK316BJ475ML D1: LUXEON EMITTER LXHL-BWO2 L1: MURATA LQH32CN150 3491 TA02b 12V to Two White LEDs at 200mA Efficiency C2 4.7µF 90 85 RSENSE 1Ω C3 1µF D1 CAP VIN 3V LED L1 15µH VIN SHUTDOWN AND DIMMING CONTROL C1 1µF LT3491 CTRL EFFICIENCY (%) PVIN 12V 20 40 60 80 100 120 140 160 180 200 LED CURRENT (mA) 80 75 70 SW 65 3491 TA03a 60 GND 0 C1, C3: TAIYO YUDEN LMK212BJ105MD C2: TAIYO YUDEN LMK316BJ475ML D1: LUXEON EMITTER LXHL-BWO2 L1: MURATA LQH32CN150 20 40 60 80 100 120 140 160 180 200 LED CURRENT (mA) 3491 TA03b 3491fa 13 LT3491 U TYPICAL APPLICATIO S Li-Ion Driver for Three White LEDs SHUTDOWN AND DIMMING CONTROL 80 CTRL 70 VIN L1 10µH C1 1µF CAP RSENSE 10Ω LT3491 SW VIN = 3.6V 3 LEDs 75 LED C2 1µF GND EFFICIENCY (%) VIN 3V TO 5V Efficiency 65 60 55 50 45 40 35 3491 TA04a 0 C1: TAIYO YUDEN LMK212BJ105MD C2: TAIYO YUDEN GMK316BJ105ML L1: MURATA LQH32CN100 2 4 3491 TA04b Li-Ion Driver for Five White LEDs Efficiency 80 SHUTDOWN AND DIMMING CONTROL 70 C1 1µF CAP RSENSE 10Ω LT3491 SW LED C2 1µF GND EFFICIENCY (%) VIN L1 10µH VIN = 3.6V 5 LEDs 75 CTRL VIN 3V TO 5V 6 8 10 12 14 16 18 20 LED CURRENT (mA) 65 60 55 50 45 40 35 0 3491 TA05a 2 4 6 8 10 12 14 16 18 20 LED CURRENT (mA) 3491 TA05b C1: TAIYO YUDEN LMK212BJ105MD C2: TAIYO YUDEN GMK316BJ105ML L1: MURATA LQH32CN100 3491fa 14 LT3491 U PACKAGE DESCRIPTIO SC8 Package 8-Lead Plastic SC70 (Reference LTC DWG # 05-08-1639 Rev Ø) 0.30 MAX 0.50 REF PIN 8 1.80 – 2.20 (NOTE 4) 1.00 REF INDEX AREA (NOTE 6) 1.80 – 2.40 1.15 – 1.35 (NOTE 4) 2.8 BSC 1.8 REF PIN 1 RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.10 – 0.40 0.15 – 0.27 8 PLCS (NOTE 3) 0.50 BSC 0.80 – 1.00 0.00 – 0.10 REF 1.00 MAX GAUGE PLANE 0.15 BSC 0.26 – 0.46 SC8 SC70 0905 REV Ø 0.10 – 0.18 (NOTE 3) NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLUSIVE OF PLATING 4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR 5. MOLD FLASH SHALL NOT EXCEED 0.254mm 6. DETAILS OF THE PIN 1 IDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED WITHIN THE INDEX AREA 7. EIAJ PACKAGE REFERENCE IS EIAJ SC-70 AND JEDEC MO-203 VARIATION BA DC Package 6-Lead DFN (2mm × 2mm) (Reference LTC DWG # 05-08-1703) R = 0.115 TYP 0.56 ± 0.05 (2 SIDES) 0.675 ±0.05 2.50 ±0.05 1.15 ±0.05 0.61 ±0.05 (2 SIDES) PACKAGE OUTLINE PIN 1 BAR TOP MARK (SEE NOTE 6) 0.38 ± 0.05 4 2.00 ±0.10 (4 SIDES) PIN 1 CHAMFER OF EXPOSED PAD 3 0.25 ± 0.05 0.50 BSC 1.42 ±0.05 (2 SIDES) 0.200 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 6 0.75 ±0.05 1 (DC6) DFN 1103 0.25 ± 0.05 0.50 BSC 1.37 ±0.05 (2 SIDES) 0.00 – 0.05 BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WCCD-2) 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm 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 3491fa 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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 15 LT3491 U TYPICAL APPLICATIO Li-Ion Driver for Six White LEDs Efficiency 80 SHUTDOWN AND DIMMING CONTROL VIN = 3.6V 6 LEDs 75 CTRL VIN L1 10µH RSENSE 10Ω LT3491 SW C1 1µF 70 CAP EFFICIENCY (%) VIN 3V TO 5V LED GND C2 1µF 65 60 55 50 45 40 0 5 10 15 20 LED CURRENT (mA) 3491 TA06b 3491 TA06a C1: TAIYO YUDEN LMK212BJ105MD C2: TAIYO YUDEN GMK316BJ105ML L1: MURATA LQH32CN100 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1618 Constant Current, Constant Voltage 1.24MHz, High Efficiency Boost Regulator Up to 16 White LEDs, VIN: 1.6V to 18V, VOUT(MAX) = 34V, IQ = 1.8mA, ISD < 1µA, MS Package LT1932 Constant Current, 1.2MHz, High Efficiency White LED Boost Regulator Up to 8 White LEDs, VIN: 1V to 10V, VOUT(MAX) = 34V, IQ = 1.2mA, ISD < 1µA, ThinSOTTM Package LT1937 Constant Current, 1.2MHz, High Efficiency White LED Boost Regulator Up to 4 White LEDs, VIN: 2.5V to 10V, VOUT(MAX) = 34V, IQ = 1.9mA, ISD < 1µA, ThinSOT/SC70 Packages LTC®3200 Low Noise, 2MHz Regulated Charge Pump White LED Driver Up to 6 White LEDs, VIN: 2.7V to 4.5V, IQ = 8mA, ISD < 1µA, MS Package LTC3200-5 Low Noise, 2MHz Regulated Charge Pump White LED Driver Up to 6 White LEDs, VIN: 2.7V to 4.5V, IQ = 8mA, ISD < 1µA, ThinSOT Package LTC3201 Low Noise, 1.7MHz Regulated Charge Pump White LED Driver Up to 6 White LEDs, VIN: 2.7V to 4.5V, IQ = 6.5mA, ISD < 1µA, MS Package LTC3202 Low Noise, 1.5MHz Regulated Charge Pump White LED Driver Up to 8 White LEDs, VIN: 2.7V to 4.5V, IQ = 5mA, ISD < 1µA, MS Package LTC3205 High Efficiency, Multidisplay LED Controller Up to 4 (Main), 2 (Sub) and RGB, VIN: 2.8V to 4.5V, IQ = 50µA, ISD < 1µA, 24-Lead QFN Package LT3465/LT3465A Constant Current, 1.2MHz/2.7MHz, High Efficiency White LED Boost Regulator with Integrated Schottky Diode Up to 6 White LEDs, VIN: 2.7V to 16V, VOUT(MAX) = 34V, IQ = 1.9mA, ISD < 1µA, ThinSOT Package LT3466/LT3466-1 Dual Full Function, 2MHz Diodes White LED Step-Up Converter with Built-In Schottkys Up to 20 White LEDs, VIN: 2.7V to 24V, VOUT(MAX) = 39V, DFN, TSSOP-16 Packages LT3486 Dual 1.3A White LED Converter with 1000:1 True Color PWM Dimming Drives Up to 16 100mA White LEDs. VIN: 2.5V to 24V, VOUT(MAX) = 36V, DFN, TSSOP Packages ThinSOT is a trademark of Linear Technology Corporation. 3491fa 16 Linear Technology Corporation LT 0406 • PRINTED IN THE USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2006