LT3465ES6

LT3465/LT3465A 1.2MHz/2.4MHz White LED Step-Up Converters with Built-In Schottky in ThinSOT FEATURES s s s s s DESCRIPTIO s s s s s Inherently Matched LED Current Drives Up to Six LEDs from a 3.6V Supply No External Schottky Diode Required 1.2MHz Switching Frequency (LT3465) 2.4MHz Switching Frequency Above AM Broadcast Band (LT3465A) Automatic Soft-Start (LT3465) Open LED Protection High Efficiency: 81% (LT3465) 79% (LT3465A) Typical Requires Only 0.22µF Output Capacitor Low Profile (1mm) SOT-23 Packaging The LT®3465/LT3465A are step-up DC/DC converters designed to drive up to six LEDs in series from a Li-Ion cell. Series connection of the LEDs provides identical LED currents and eliminates the need for ballast resistors. These devices integrate the Schottky diode required externally on competing devices. Additional features include output voltage limiting when LEDs are disconnected, onepin shutdown and dimming control. The LT3465 has internal soft-start. The LT3465 switches at 1.2MHz, allowing the use of tiny external components. The faster LT3465A switches at 2.4MHz. Constant frequency switching results in low input noise and a small output capacitor. Just 0.22µF is required for 3-, 4- or 5-LED applications. The LT3465 and LT3465A are available in low profile (1mm) 6-lead SOT-23 (ThinSOTTM) packages. , LTC and LT are registered trademarks of Linear Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation. APPLICATIO S s s s s s Cellular Phones PDAs, Handheld Computers Digital Cameras MP3 Players GPS Receivers TYPICAL APPLICATIO L1 22µH 3V TO 5V Conversion Efficiency 82 VIN = 3.6V 80 4 LEDs 78 EFFICIENCY (%) SW VIN SHUTDOWN AND DIMMING CONTROL C1 1µF LT3465/ LT3465A CTRL FB GND C2 0.22µF 10Ω 3465A F01a VOUT 76 74 72 70 68 66 64 62 60 0 5 10 LED CURRENT (mA) 3465A F01b C1, C2: X5R OR X7R DIELECTRIC L1: MURATA LQH32CN220 Figure 1. Li-Ion Powered Driver for Four White LEDs U LT3465 LT3465A 15 20 3465af U U 1 LT3465/LT3465A ABSOLUTE (Note 1) AXI U RATI GS PACKAGE/ORDER I FOR ATIO TOP VIEW VOUT 1 GND 2 FB 3 6 SW 5 VIN 4 CTRL Input Voltage (VIN) ................................................. 16V SW Voltage ............................................................. 36V FB Voltage ................................................................ 2V CTRL Voltage .......................................................... 10V 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, 10 sec)................. 300°C ORDER PART NUMBER LT3465ES6 LT3465AES6 S6 PART MARKING LTH2 LTAFT S6 PACKAGE 6-LEAD PLASTIC TSOT-23 TJMAX = 125°C, θJA = 256°C/W IN FREE AIR θJA = 120°C ON BOARD OVER GROUND PLANE Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS PARAMETER Minimum Operating Voltage Maximum Operating Voltage Feedback Voltage FB Pin Bias Current Supply Current Switching Frequency Maximum Duty Cycle Switch Current Limit Switch VCESAT Switch Leakage Current VCTRL for Full LED Current VCTRL to Shut Down Chip CTRL Pin Bias Current TA = 85°C TA = – 40°C Soft-Start Time Schottky Forward Drop Schottky Leakage Current ID = 150mA VR = 30V ISW = 250mA VSW = 5V Not Switching CTRL = 0V 0°C ≤ TA ≤ 85°C CONDITIONS The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 3V, VCTRL = 3V, unless otherwise noted. MIN 2.7 16 188 10 1.9 2.0 0.8 q q LT3465 TYP MAX MIN 2.7 LT3465A TYP MAX 16 UNITS V V mV nA mA µA MHz % mA mV 200 35 2.6 3.2 1.2 93 340 300 0.01 212 100 3.3 5.0 1.6 188 10 1.9 2.0 1.8 90 225 200 35 2.6 3.2 2.4 93 340 300 0.01 212 100 3.3 5.0 2.8 90 225 5 1.8 50 5 50 1.8 48 40 60 60 50 75 600 0.7 4 72 60 90 48 40 60 60 50 75 0.7 72 60 90 4 Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LT3465E/LT3465AE are guaranteed to meet performance specifications from 0°C to 70°C. Specifications over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls. 2 U µA V mV µA µA µA µs V µA 3465af W U U WW W LT3465/LT3465A TYPICAL PERFOR A CE CHARACTERISTICS Switch Saturation Voltage (VCESAT) 450 SWITCH SATURATION VOLTAGE (mV) TA = 25°C SCHOTTKY FORWARD CURRENT (mA) 400 350 300 250 200 150 100 50 0 0 50 100 150 200 250 SWITCH CURRENT (mA) 300 350 150 100 50 0 IQ (µA) VFB vs VCTRL 250 TA = 25°C OUTPUT CLAMP VOLTAGE (V) FEEDBACK VOLTAGE (mV) 200 25 20 15 10 5 INPUT CURRENT (mA) 150 100 50 0 0 1 0.5 1.5 CONTROL VOLTAGE (V) Switching Waveforms (LT3465) VSW 10V/DIV IL 100mA/DIV VOUT 100mV/DIV VSW 10V/DIV IL 50mA/DIV VOUT 50mV/DIV VIN = 3.6V 4 LEDs 20mA, 22µH 200ns/DIV SWITCHING FREQUENCY (MHz) UW 3465A G01 Schottky Forward Voltage Drop 300 250 200 TA = 25°C Shutdown Quiescent Current (CTRL = 0V) 30 27 24 21 18 15 12 9 6 3 TA = 25°C 0 1000 400 600 800 200 SCHOTTKY FORWARD DROP (mV) 1200 0 2 4 6 10 8 VIN (V) 12 14 16 3465A G02 3465A G03 Open-Circuit Output Clamp Voltage 35 30 TA = 25°C Input Current in Output Open Circuit 5 TA = 25°C 4 3 2 1 0 0 2 4 10 8 12 6 INPUT VOLTAGE (V) 14 16 2 3465A G04 2 2.5 4 3 3.5 INPUT VOLTAGE (V) 4.5 5 3465A G05 3465A G06 Switching Waveforms (LT3465A) 3.0 2.5 2.0 1.5 Switching Frequency LT3465A LT3465 1.0 0.5 0 –50 3465A G07a VIN = 3.6V 4 LEDs 20mA, 22µH 100ns/DIV 3465A G07b 50 0 TEMPERATURE (°C) 100 4365A G08 3465af 3 LT3465/LT3465A TYPICAL PERFOR A CE CHARACTERISTICS Feedback Voltage 210 208 FEEDBACK VOLTAGE (mV) 3.0 2.5 2.0 IQ (mA) 206 204 202 200 198 196 194 192 190 –50 –30 –10 10 30 50 TEMPERATURE (°C) CURRENT LIMIT (mA) –50°C 25°C 100°C 0 5 10 VIN (V) 15 20 3465A G10 VIN = 3.6V, 4 LEDs 85 SCHOTTKY LEAKAGE CURRENT (µA) LT3465 LT3465A 80 EFFICIENCY (%) 75 15mA 10mA 70 65 60 –50 50 0 TEMPERATURE (°C) PI FU CTIO S VOUT (Pin 1): Output Pin. Connect to output capacitor and LEDs. Minimize trace between this pin and output capacitor to reduce EMI. GND (Pin 2): Ground Pin. Connect directly to local ground plane. FB (Pin 3): Feedback Pin. Reference voltage is 200mV. Connect LEDs and a resistor at this pin. LED current is determined by the resistance and CTRL pin voltage: 200mV When VCTRL > 1.8 V RFB V ILED ≈ CTRL When VCTRL < 1V 5 • RFB ILED ≈ 3465af 4 UW 70 90 3465A G09 Quiescent Current (CTRL = 3V) 400 350 300 250 200 150 100 50 0 Switching Current Limit 1.5 1.0 0.5 0 –50°C 25°C 100°C 0 20 40 60 DUTY CYCLE (%) 80 100 3465A G11 Schottky Leakage Current 8 20mA 7 VR = 25 6 5 4 3 2 1 0 –50 0 50 100 3465A G13 VR = 16 VR = 10 100 3465A G12 TEMPERATURE (°C) U U U CTRL (Pin 4): Dimming Control and Shutdown Pin. Ground this pin to shut down the device. When VCTRL is greater than about 1.8V, full-scale LED current is generated. When VCTRL is less than 1V, LED current is reduced. VIN (Pin 5): Input Supply Pin. Must be locally bypassed with a 1µF X5R or X7R type ceramic capacitor. SW (Pin 6): Switch Pin. Connect inductor here. LT3465/LT3465A BLOCK DIAGRA VIN 5 A1 RC CC Σ 10k RAMP GENERATOR 40k CTRL 4 1.2MHz* OSCILLATOR Figure 2. LT3465 Block Diagram APPLICATIO S I FOR ATIO Operation The LT3465 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 2. At the start of each oscillator cycle, the SR latch is set, which turns on the power switch Q1. 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 SR latch is reset turning 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 feedback voltage and the reference voltage of 200mV. In this manner, the error amplifier sets the correct peak current level to keep the output in regulation. If the error amplifier’s output increases, more current is delivered to the output; if it decreases, less current is delivered. The CTRL pin voltage is used to adjust the reference voltage. The block diagram for the LT3465A (not shown) is identical except that the oscillator frequency is 2.4MHz. Minimum Output Current The LT3465 can drive a 3-LED string at 1.5mA LED current without pulse skipping. As current is further reduced, the device will begin skipping pulses. This will + – VREF 1.25V U W W FB 3 6 SW COMPARATOR DRIVER A2 R S Q Q1 OVERVOLTAGE PROTECT 200mV – + + VOUT 1 + 0.2Ω – 2 GND 3465A F02 *2.4MHz FOR LT3465A UU result in some low frequency ripple, although the LED current remains regulated on an average basis down to zero. The photo in Figure 3a details circuit operation driving three white LEDs at a 1.5mA load. Peak inductor current is less than 40mA and the regulator operates in discontinuous mode, meaning the inductor current VSW 5V/DIV IL 20mA/DIV VOUT 10mV/DIV VIN = 4.2V ILED = 1.5mA 3 LEDs 0.2µs/DIV 3465A F03a Figure 3a. Switching Waveforms (LT3465) VSW 5V/DIV IL 20mA/DIV VOUT 10mV/DIV VIN = 4.2V ILED = 0.2mA 3 LEDs 0.1µs/DIV 3465A F03b Figure 3b. Switching Waveforms (LT3465A) 3465af 5 LT3465/LT3465A APPLICATIO S I FOR ATIO 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 switch and diode capacitance. This ringing is not harmful; far less spectral energy is contained in the ringing than in the switch transitions. The ringing can be damped by application of a 300Ω resistor across the inductor, although this will degrade efficiency. Because of the higher switching frequency, the LT3465A can drive a 3-LED string at 0.2mA LED current without pulse skipping. The photo in Figure 3b detials circuit operation driving three white LEDs at a 0.2mA load. Peak inductor current is less than 30mA. Inductor Selection A 22µH inductor is recommended for most LT3465 applications. Although small size and high efficiency are major concerns, the inductor should have low core losses at 1.2MHz and low DCR (copper wire resistance). Some inductors in this category with small size are listed in Table 1. The efficiency comparison of different inductors is shown in Figure 4a. A 22µH or 10µH inductor is recommended for most LT3465A applications. The inductor should have low core losses at 2.4MHz and low DCR. The efficiency comparison of different inductors is shown in figure 4b. Table 1. Recommended Inductors PART NUMBER LQH32CN220 LQH2MCN220 ELJPC220KF DCR (Ω) 0.71 2.4 4.0 CURRENT RATING (mA) 250 185 160 MANUFACTURER Murata 814-237-1431 www.murata.com Panasonic 714-373-7334 www.panasonic.com Sumida 847-956-0666 www.sumida.com Taiyo Yuden 408-573-4150 www.t-yuden.com Taiyo Yuden 408-573-4150 www.t-yuden.com 80 75 VIN = 3.6V 4 LEDs EFFICIENCY (%) EFFICIENCY (%) CDRH3D16-220 0.53 350 LB2012B220M 1.7 75 LEM2520-220 5.5 125 6 U 85 80 75 70 65 60 55 50 0 5 10 LED CURRENT (mA) 3465A F04b W UU VIN = 3.6V 4 LEDs MURATA LQH32CN220 TAIYO YUDEN LB2012B220M TAIYO YUDEN CB2012B220 15 20 Figure 4a. Efficiency Comparison of Different Inductors (LT3465) 70 65 60 55 50 0 5 MURATA LQH32CN220 MURATA LQH32CN100 MURATA LQH2MCN220 TOKO D312-220 TOKO D312-100 TAIYO YUDEN LB2012B220 10 LED CURRENT (mA) 3465A F04b 15 20 Figure 4b. Efficiency Comparison of Different Inductors (LT3465A) Capacitor Selection The small size of ceramic capacitors makes them ideal for LT3465 and LT3465A applications. X5R and X7R types are recommended because they retain their capacitance over wider voltage and temperature ranges than other types such as Y5V or Z5U. A 1µF input capacitor and a 0.22µF output capacitor are sufficient for most LT3465 and LT3465A applications. Table 2. Recommended Ceramic Capacitor Manufacturers MANUFACTURER Taiyo Yuden Murata Kemet PHONE 408-573-4150 814-237-1431 408-986-0424 URL www.t-yuden.com www.murata.com www.kemet.com 3465af LT3465/LT3465A APPLICATIO S I FOR ATIO Soft-Start (LT3465) The LT3465 has an internal soft-start circuit to limit the input current during circuit start-up. The circuit start-up waveforms are shown in Figure 5. IIN 50mA/DIV VOUT 5V/DIV VFB 100mV/DIV CTRL 5V/DIV VIN = 3.6V 4 LEDs, 20mA L = 22µH C = 0.22µF 200µs/DIV 3465 F05 Figure 5. Start-Up Waveforms Inrush Current The LT3465 and LT3465A have a built-in Schottky diode. When supply voltage is applied to the VIN pin, the voltage difference between VIN and VOUT generates inrush current flowing from input through the inductor and the Schottky diode to charge the output capacitor to VIN. The maximum current the Schottky diode in the LT3465 and LT3465A can sustain is 1A. The selection of inductor and capacitor value should ensure the peak of the inrush current to be below 1A. The peak inrush current can be calculated as follows: IP = α= ω= α  VIN – 0.6  ω  ω • exp – • arctan   • sinarctan    α  α L•ω ω  r + 1.5 2 •L (r + 1.5) 1 – L •C 4 • L2 2 where L is the inductance, r is the resistance of the inductor and C is the output capacitance. For low DCR inductors, which is usually the case for this application, the peak inrush current can be simplified as follows: IP = VIN – 0.6  α π • exp – •   ω 2 L•ω U Table 3 gives inrush peak currents for some component selections. Table 3. Inrush Peak Current VIN (V) 5 5 3.6 5 r (Ω) 0.5 0.5 0.5 0.5 L (µH) 22 22 22 33 C (µF) 0.22 1 0.22 1 IP (A) 0.38 0.70 0.26 0.60 W UU LED Current and Dimming Control The LED current is controlled by the feedback resistor (R1 in Figure 1) and the feedback reference voltage. ILED = VFB/RFB The CTRL pin controls the feedback reference voltage as shown in the Typical Performance Characteristics. For CTRL higher than 1.8V, the feedback reference is 200mV, which results in full LED current. CTRL pin can be used as dimming control when CTRL voltage is between 200mV to 1.5V. In order to have accurate LED current, precision resistors are preferred (1% is recommended). The formula and table for RFB selection are shown below. RFB = 200mV/ILED-Full Table 4. RFB Resistor Value Selection FULL ILED (mA) 5 10 15 20 R1 (Ω) 40.0 20.0 13.3 10.0 (1) The filtered PWM signal can be considered as an adjustable DC voltage. It can be used to adjust the CTRL voltage source in dimming control. The circuit is shown in Figure 6. The corner frequency of R1 C1 should be lower than the freqency of the PWM signal. R1 needs to be much smaller than the internal impedance in the CTRL pin, which is 50kΩ. R1 5k PWM C1 100nF LT3465/ LT3465A CTRL 3465A F06 Figure 6. Dimming Control Using a Filtered PWM Signal 3465af 7 LT3465/LT3465A APPLICATIO S I FOR ATIO Dimming Using Direct PWM (LT3465A) Unlike the LT3465, the LT3465A does not have internal soft-start. Although the input current is higher during startup, the absence of soft-start allows the CTRL pin to be directly driven with a PWM signal for dimming. A zero percent duty cycle sets the LED current to zero, while 100% duty cycle sets it to full current. Average LED current increases proportionally with the duty cycle of the PWM signal. PWM frequency should be between 1kHz and 10kHz for best performance. The PWM signal should be at least 1.8V in magnitude; lower voltage will lower the feedback voltage as shown in Equation 1. Waveforms are shown for a 1kHz PWM and 10kHz PWM signal in Figures 7a and 7b respectively. LT3465A PWM CTRL FB 100mV/DIV RFB CTRL 2V/DIV 200µs/DIV (1kHz) 3465A F07a Figure 7a. FB 100mV/DIV CTRL 2V/DIV 20µs/DIV (10kHz) 3465A F07b Figure 7b. Open-Circuit Protection The LT3465 and LT3465A have 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, the VOUT is clamped at 30V. The LT3465 and LT3465A will then switch at a very low frequency to 8 U minimize the input current. VOUT and input current during output open circuit are shown in the Typical Performance Characteristics. Board Layout Consideration As with all switching regulators, careful attention must be paid to the PCB board layout and component placement. To maximize efficiency, switch rise and fall times are made as short as possible. To prevent electromagnetic interference (EMI) problems, proper layout of the high frequency switching path is essential. Place COUT next to the VOUT pin. Always use a ground plane under the switching regulator to minimize interplane coupling. In addition, the ground connection for the feedback resistor R1 should be tied directly to the GND pin and not shared with any other component, ensuring a clean, noise-free connection. Recommended component placement is shown in Figure 8. GND COUT L 1 2 3 6 5 4 VIN CTRL 3465A F08 W UU CIN Figure 8. Recommended Component Placement Start-Up Input Current (LT3465A) As previously mentioned, the LT3465A does not have an internal soft-start circuit. Inrush current can therefore rise to approximately 400mA as shown in Figure 9 when driving 4 LEDs. The LT3465 has an internal soft-start circuit and is recommended if inrush current must be minimized. IIN 200mV/DIV FB 200mV/DIV CTRL 2V/DIV 50µs/DIV 3465A F09 Figure 9. 3465af LT3465/LT3465A TYPICAL APPLICATIO S Li-Ion to Two White LEDs L1 22µH 3V TO 5V 85 80 VIN = 3.6V 2 LEDs VIN CIN 1µF LT3465/ LT3465A FB CTRL GND COUT 1µF R1 4Ω 3465A TA01a EFFICIENCY (%) SW VOUT CIN: TAIYO YUDEN JMK107BJ105 COUT: AVX 0603ZD105 L1: MURATA LQH32CN220 L1 22µH 3V TO 5V SW VIN CIN 1µF VOUT COUT 0.22µF R1 10Ω 3465A TA02a EFFICIENCY (%) LT3465/ LT3465A FB CTRL GND CIN: TAIYO YUDEN JMK107BJ105 COUT: AVX 0603YD224 L1: MURATA LQH32CN220 U 75 70 65 60 55 50 0 10 30 20 LED CURRENT (mA) LT3465 LT3465A 40 50 3465A TA01b Li-Ion to Three White LEDs 85 80 75 70 65 60 55 50 0 5 15 10 LED CURRENT (mA) LT3465 LT3465A 20 3465A TA02b VIN = 3.6V 3 LEDs 3465af 9 LT3465/LT3465A TYPICAL APPLICATIO S Li-Ion to Five White LEDs L1 22µH 3V TO 5V EFFICIENCY (%) 10 U SW VIN CIN 1µF VOUT COUT 0.22µF R1 10Ω 3465A TA03a LT3465/ LT3465A FB CTRL GND CIN: TAIYO YUDEN JMK107BJ105 COUT: TAIYO YUDEN GMK212BJ224 L1: MURATA LQH32CN220 85 80 75 70 65 60 55 50 0 VIN = 3.6V 5 LEDs LT3465 LT3465A 5 15 10 LED CURRENT (mA) 20 3465A TA03b 3465af LT3465/LT3465A PACKAGE DESCRIPTIO 0.62 MAX 0.95 REF 3.85 MAX 2.62 REF RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.20 BSC 1.00 MAX DATUM ‘A’ 0.30 – 0.50 REF 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. JEDEC PACKAGE REFERENCE IS MO-193 0.09 – 0.20 (NOTE 3) 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. U S6 Package 6-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1636) 2.90 BSC (NOTE 4) 1.22 REF 1.4 MIN 2.80 BSC 1.50 – 1.75 (NOTE 4) PIN ONE ID 0.95 BSC 0.30 – 0.45 6 PLCS (NOTE 3) 0.80 – 0.90 0.01 – 0.10 1.90 BSC S6 TSOT-23 0302 3465af 11 LT3465/LT3465A TYPICAL APPLICATIO L1 47µH/22µH 3V TO 5V VIN CIN 1µF LT3465/ LT3465A CTRL FB GND COUT 0.47µF R1 10Ω 3465A TA04a EFFICIENCY (%) SW VOUT CIN: TAIYO YUDEN JMK107BJ105 COUT: TAIYO YUDEN GMK212BJ474 L1: MURATA LQH32CN470 (LT3465) L1: MURATA LQH32CN220 (LT3465A) RELATED PARTS PART NUMBER DESCRIPTION LT1618 Constant Current, Constant Voltage, 1.4MHz, High Efficiency Boost Regulator LT1932 Constant Current, 1.2MHz, High Efficiency White LED Boost Regulator LT1937 Constant Current, 1.2MHz, High Efficiency White LED Boost Regulator LTC®3200-5 Low Noise, 2MHz, Regulated Charge Pump White LED Driver LTC3202 Low Noise, 1.5MHz, Regulated Charge Pump White LED Driver LTC3205 LTC3405 LTC3405A LTC3406 LTC3406B LTC3407 LTC3411 LTC3412 LTC3440/ LTC3441 LT3466 COMMENTS Up to 16 White LEDs, VIN: 1.6V to 18V, VOUT(MAX): 34V, IQ: 1.8mA, ISHDN: