LT3473

FEATURES ■ ■ ■ ■ ■ LT3498 20mA LED Driver and OLED Driver with Integrated Schottky in 3mm x 2mm DFN DESCRIPTION The LT®3498 is a dual output boost converter featuring a 2.3MHz PWM LED Driver and PFM OLED Driver. It includes an internal power switch and Schottky diode for each driver. Both converters can be independently shut down and modulated. This highly integrated power solution is ideal for dual display electronic devices. The 2.3MHz step-up converter is designed to drive up to six white LEDs in series from a Li-Ion cell. 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. Traditional LED drivers use a grounded resistor to sense LED current, requiring a 2-wire connection to the LED string. The PFM OLED driver is a low noise boost converter that features a novel control technique.* The converter controls power delivery by varying both the peak inductor current and switch off time. This technique results in low output voltage ripple, as well as, high efficiency over a wide load range. The off time of the switch is not allowed to exceed a fixed level, guaranteeing a switching frequency that stays above the audio band. , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. *Patent Pending ■ ■ ■ ■ ■ ■ ■ ■ Dual Output Boost for Dual Display Devices Drives Up to Six White LEDs and OLED/LCD Bias Internal Power Switches and Schottky Diodes Independent Dimming and Shutdown 200mV High Side Sense on LED Driver Allows “One-Wire Current Source” Wide Input Voltage Range: 2.5V to 12V Wide Output Voltage Range: Up to 32V 2.3MHz PWM Frequency for LED Driver PFM for OLED Driver is Non-Audible Over Entire Load Range Open LED Protection (27V Maximum on CAP1 Pin) OLED Output Disconnect Available in 12-Pin DFN Package 1mm Tall Solution Height APPLICATIONS ■ ■ ■ ■ ■ Cellular Phones PDAs, Handheld Computers Digital Cameras MP3 Players GPS Receivers TYPICAL APPLICATION Li-Ion to Six White LEDs and OLED/LCD Bias 80 VIN = 3V TO 5V 4.7µF 0.47µF OLED Efficiency 75 70 EFFICIENCY (%) 16V 24mA VIN = 3.6V VOUT2 = 16V LOAD FROM VOUT2 400 350 300 POWER LOSS (mW) 250 200 150 100 15µH 1µF 10Ω CAP1 SW1 VIN 15µH SW2 CAP2 VOUT2 65 60 55 50 45 40 0.1 POWER LOSS FROM VOUT2 1 10 LED CURRENT (mA) 10µF LT3498 LED1 20mA CTRL1 OFF ON SHUTDOWN AND DIMMING CONTROL 3498 TA01 GND1 GND2 CTRL2 OFF ON SHUTDOWN AND CONTROL FB2 2.21MΩ 50 0 100 3498 TA01b 3498f 1 LT3498 ABSOLUTE MAXIMUM RATINGS (Notes 1, 2) PACKAGE/ORDER INFORMATION TOP VIEW LED1 1 CTRL1 2 GND1 3 GND2 4 CTRL2 5 FB2 6 13 12 CAP1 11 SW1 10 VIN 9 SW2 8 CAP2 7 VOUT2 Input Voltage (VIN) ....................................................12V CTRL1 and CTRL2 Voltage ........................................12V FB2 Voltage ..............................................................2.5V VOUT2 Voltage ...........................................................32V SW1 and SW2 Voltage ..............................................32V CAP1 and CAP2 Voltage ............................................32V LED1 Voltage ............................................................32V Operating Junction Temperature Range ...–40°C to 85°C Maximum Junction Temperature .......................... 125°C Storage Temperature Range...................–65°C to 150°C DDB PACKAGE 12-LEAD (3mm × 2mm) PLASTIC DFN TJMAX = 125°C, θJA = 160°C/W EXPOSED PAD (PIN 13) IS GND, MUST BE SOLDERED TO PCB ORDER PART NUMBER LT3498EDDB DDB PART MARKING LCQF 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 PARAMETER Minimum Operating Voltage Maximum Operating Voltage Supply Current (LED Off, OLED Off) Supply Current (LED On, OLED Off) Supply Current (LED Off, OLED On) Supply Current (LED On, OLED On) VCTRL1 for Full LED Current VCTRL2 for Full OLED Brightness VCTRL1 or VCTRL2 to Turn On IC VCTRL1 and VCTRL2 to Shut Down IC CTRL1, CTRL2 Pin Bias Current LED Driver LED Current Sense Voltage (VCAP – VLED) CAP1, LED1 Pin Bias Current VCAP1, VLED1 Common Mode Minimum Voltage Switching Frequency Maximum Duty Cycle Switch Current Limit Switch VCESAT The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C, VIN = 3V, VCTRL1 = VCTRL2 = 3V. CONDITIONS MIN 2.5 12 VIN = 3V, VCTRL1 = 0V, VCTRL2 = 0V VIN = 3V, VCTRL1 = 3V, VCTRL2 = 0V, VCAP1 = 24V, VLED1 = 23V VIN = 3V, VCTRL1 = 0V, VCTRL2 = 3V, VFB2 = 3V VIN = 3V, VCTRL1 = 3V, VCTRL2 = 3V, VCAP1 = 24V, VLED1 = 23V ● TYP MAX UNITS V V µA mA µA mA V mV 8 1.6 230 1.65 1.5 125 10 2 280 2.05 ● ● 75 100 mV nA VCAP1 = 24V, ISW = 200mA VCAP1 = 16V, VLED1 = 16V ● 190 200 20 210 30 2.5 2.8 mV µA V MHz % mA mV 3498f ● 1.8 88 300 2.3 90 425 250 ● ISW = 200mA 2 LT3498 ELECTRICAL CHARACTERISTICS PARAMETER Switch Leakage Current CAP1 Pin Overvoltage Protection Schottky Forward Voltage Schottky Reverse Leakage OLED Driver Feedback Voltage Feedback Resistor Minimum Switch Off Time Minimum Switch Off Time Maximum Switch Off Time Switch Current Limit Switch VCESAT Switch Leakage Current Schottky Forward Voltage Schottky Reverse Leakage PMOS Disconnect VCAP2 – VOUT2 CTRL2 to FB2 Offset Maximum Shunt Current ISW2 = 200mA VSW2 = 16V ISCHOTTKY2 = 100mA VREVERSE2 = 20V IOUT2 = 10mA, VCAP2 = 5V VCTRL2 = 0.5V VFB2 = 1.3V 250 8 220 15 After Start-Up During Start-Up (Note 4) VFB2 = 1.5V ● The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C, VIN = 3V, VCTRL1 = VCTRL2 = 3V. CONDITIONS VSW1 = 16V 26 ISCHOTTKY1 = 100mA VREVERSE1 = 20V VCTRL2 = 3V (Note 3) ● ● MIN TYP 0.1 27 0.8 MAX 5 28 6 UNITS µA V V µA V kΩ ns µs 1.18 177 1.215 182 150 1 1.25 186 15 180 20 300 260 0.1 800 30 400 5 2 µs mA mV µA mV µA mV mV µA 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 LT3498 is guaranteed to meet performance specifications from 0°C to 85°C. Specifications over the –40°C to 85°C junction operating temperature range are assured by design, characterization and correlation with statistical process controls. Note 3: Internal reference voltage is determined by finding VFB2 voltage level which causes quiescent current to increase 20µA above “Not Switching” level. Note 4: If CTRL2 is overriding the internal reference, start-up mode occurs when VFB2 is less then half the voltage on CTRL2. If CTRL2 is not overriding the internal reference, start-up mode occurs when VFB2 is less then half the voltage of the internal reference. 3498f 3 LT3498 TYPICAL PERFORMANCE CHARACTERISTICS Shutdown Current (VCTRL1 = VCTRL2 = 0V) 15 SWITCH SATURATION VOLTAGE (mV) T = –50°C 500 SCHOTTKY FORWARD CURRENT (mA) 450 400 350 300 250 200 150 100 50 0 0 2 4 6 VIN (V) 8 10 12 1635 G07 TA = 25°C, unless otherwise specified. LED Schottky Forward Voltage Drop 400 350 300 250 200 150 100 50 0 0 T = –50°C T = 25°C LED Switch Saturation Voltage (VCESAT1) T = –50°C SHUTDOWN CURRENT (µA) 12 T = 125°C 9 T = 125°C 6 T = 25°C T = 25°C T = 125°C 3 0 0 50 100 150 200 250 300 350 400 SWITCH CURRENT (mA) 3498 G02 200 400 800 600 SCHOTTKY FORWARD DROP (mV) 1000 3498 G03 Sense Voltage (VCAP1 – VLED1) vs VCTRL1 240 200 SENSE VOLTAGE (mV) 160 120 80 40 0 0 500 1000 VCTRL1 (mV) 1500 2000 3498 G04 Sense Voltage (VCAP1 – VLED1) vs Temperature 206 206 Sense Voltage (VCAP1 – VLED1) vs VCAP1 T = 25°C T = –50°C T = 125°C SENSE VOLTAGE (mV) 202 SENSE VOLTAGE (mV) 202 198 198 T = 125°C T = 25°C T = –50°C 194 194 190 190 186 –50 –25 50 25 0 75 TEMPERATURE (°C) 100 125 186 0 5 15 10 CAP1 VOLTAGE (V) 20 25 3498 G06 3498 G05 LED Current Limit vs Temperature 500 29 Open Circuit Output Clamp Voltage 6 5 INPUT CURRENT (mA) 28 T = –50°C T = 25°C T = 150°C 4 3 Input Current in Output Open Circuit CURRENT LIMIT (mA) 450 OUTPUT CLAMP VOLTAGE (V) T = 150°C T = 25°C T = –50°C 400 27 2 1 350 26 300 –50 –25 50 25 0 75 TEMPERATURE (°C) 100 125 25 0 0 2 4 6 VIN (V) 8 10 12 3498 G08 2 4 6 VIN (V) 8 10 12 3498 G09 3498 G07 3498f 4 LT3498 TYPICAL PERFORMANCE CHARACTERISTICS LED Switching Frequency vs Temperature 2.6 LED SWITCHING FREQUENCY (MHz) 2.5 2.4 2.3 2.2 2.1 2.0 1.9 1.8 – 50 – 25 0 50 75 25 TEMPERATURE (°C) 100 125 SWITCH SATURATION VOLTAGE (mV) 300 SCHOTTKY FORWARD CURRENT (mA) 250 200 150 100 50 0 T = 25°C T = 125°C T = –50°C TA = 25°C, unless otherwise specified. OLED Schottky Forward Voltage Drop 400 350 T = 125°C 300 250 200 150 100 50 0 0 200 400 800 1000 600 SCHOTTKY FORWARD DROP (mV) 1200 T = 25°C OLED Switch Saturation Voltage (VCESAT2) T = –50°C 0 50 250 100 150 200 SWITCH CURRENT (mA) 300 3498 G10 3498 G11 3498 G12 VOUT2 vs VCTRL2 (VOUT2 = 16V) 18 16 OUTPUT VOLTAGE CHANGE (%) 14 VOUT2 VOLTAGE (V) 12 10 8 6 4 2 0 0 500 1500 1000 CTRL2 VOLTAGE (V) 2000 3498 G13 VOUT2 vs Temperature (VOUT2 = 16V) 6 2.0 1.5 3 VOUT2 VOLTAGE CHANGE (%) –25 50 25 0 75 TEMPERATURE (°C) 100 125 1.0 0.5 0 –0.5 –1.0 –1.5 –6 –50 –2.0 VOUT2 Load Regulation 0 –3 0 10 20 40 30 LOAD CURRENT (mA) 50 3498 G15 3498 G14 OLED Minimum Switching Frequency 80 70 SWITCHING FREQUENCY (kHz) 60 50 40 30 20 10 0 – 50 – 25 0 50 75 25 TEMPERATURE (°C) 100 125 SWITCHING FREQUENCY (kHz) 1200 1000 800 600 400 200 0 OLED Switching Frequency vs Load Current 600 PEAK INDUCTOR CURRENT (mA) 0.1 1 10 LOAD CURRENT (mA) 100 3498 G17 Peak Inductor Current 550 500 450 400 350 300 250 200 – 50 – 25 0 50 75 25 TEMPERATURE (°C) 100 125 3498 G16 3498 G18 3498f 5 LT3498 TYPICAL PERFORMANCE CHARACTERISTICS LED Switching Waveforms VSW 10V/DIV VCAP1 5V/DIV VCTRL1 5V/DIV TA = 25°C, unless otherwise specified. OLED Switching Waveforms with No Load VOUT2 10mV/DIV AC COUPLED LED Transient Response VCAP1 50mV/DIV IL 100mA/ DIV 500ns/DIV VIN = 3.6V FRONT PAGE APPLICATION 3498 G19 SW2 VOLTAGE 10V/DIV IL 200mA/ DIV 1ms/DIV VIN = 3.6V FRONT PAGE APPLICATION 3498 G20 INDUCTOR CURRENT 50mA/DIV VIN = 3.6V VOUT2 = 16V 5µs/DIV 3498 G21 OLED Switching Waveforms with 4mA Load VOUT2 10mV/DIV AC COUPLED SW2 VOLTAGE 10V/DIV INDUCTOR CURRENT 200mA/DIV VIN = 3.6V VOUT2 = 16V VOUT2 10mV/DIV AC COUPLED SW2 VOLTAGE 10V/DIV INDUCTOR CURRENT 200mA/DIV 2µs/DIV 3498 G22 OLED Switching Waveforms with 35mA Load CAP2 VOLTAGE 5V/DIV VOUT2 VOLTAGE 5V/DIV OLED Switching Waveforms During Start-Up VIN = 3.6V VOUT2 = 16V 500ns/DIV 3498 G23 INDUCTOR CURRENT 100mA/DIV VIN = 3.6V VOUT2 = 16V 500µs/DIV 3498 G24 PIN FUNCTIONS LED1 (Pin 1): Connection Point Between the Anode of the Highest LED and the Sense Resistor. The LED current can be programmed by: 200mV ILED1 = RSENSE1 CTRL1 (Pin 2): Dimming and Shutdown Pin. Connect this pin below 75mV to disable the white LED driver. As the pin voltage is ramped from 0V to 1.5V, the LED current ramps from 0 to (ILED1 = 200mV / RSENSE1). GND1, 2 (Pins 3, 4): Ground. Tie directly to local ground plane. GND1 and GND2 are connected internally. CTRL2 (Pin 5): Dimming and Shutdown Pin. Connect it below 75mV to disable the low noise boost converter. As the pin voltage is ramped from 0V to 1.5V, the output ramps up to the programmed output voltage. FB2 (Pin 6): Feedback Pin. Reference voltage is 1.215V. There is an internal 182kΩ resistor from FB2 to GND. To achieve desired output voltage, choose RFB2 according to the following formula: ⎞ ⎛V RFB2 = 182 • ⎜ OUT2 − 1⎟ kΩ ⎝ 1.215 ⎠ 3498f 6 LT3498 PIN FUNCTIONS VOUT2 (Pin 7): Drain of Output Disconnect PMOS. Place a bypass capacitor from this pin to GND. See the Applications Information section. CAP2 (Pin 8): Output of the OLED Driver. This pin is connected to the cathode of the internal Schottky diode. Place a bypass capacitor from this pin to GND. SW2 (Pin 9): Switch Pin. This is the collector of the internal NPN power switch. Minimize the metal trace area connected to this pin to minimize EMI. VIN (Pin 10): Input Supply Pin. Must be locally bypassed. SW1 (Pin 11): Switch Pin. Connect the inductor of the white LED driver at this pin. Minimize metal trace area at this pin to minimize EMI. CAP1 (Pin 12): Output of the White LED Driver. This pin is connected to the cathode of the internal Schottky. Connect the output capacitor to this pin and the sense resistor from this pin to the LED1 pin. Exposed Pad (Pin 13): Ground. The Exposed Pad must be soldered to the PCB. BLOCK DIAGRAM L2 10µF CIN 4.7µF 9 CAP2 8 C2 0.47µF START-UP CONTROL SW2 10 VIN 11 SW1 Q S DRIVER Q1 OVERVOLTAGE PROTECTION L1 15µF COMPARATOR CAP1 12 – A2 R + + Σ RAMP GENERATOR VOUT2 7 C3 10µF Q2 DISCONNECT CONTROL RC SHUNT CONTROL RFB2 2.21MΩ A5 CC DRIVER SWITCH CONTROL 2.3MHz OSCILLATOR A3 R – RSENSE1 10Ω C1 1µF + A1 – + + A4 LED1 – 1 + + – VREF 182kΩ GND2 4 FB2 6 5 CTRL2 CTRL1 GND1 2 3 3498 BD 3498f 7 LT3498 OPERATION—LED DRIVER The LED portion of the LT3498 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. At power-up, the capacitor at the CAP1 pin is charged up to VIN (input supply voltage) through the inductor and the internal Schottky diode. If CTRL1 is pulled higher than 125mV, 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 VCAP1 and VLED1 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 CTRL1 pin is used to adjust the LED current. The LED Driver is shutdown when CTRL1 is pulled lower than 75mV. Minimum Output Current The LED Driver of the LT3498 can drive a 4-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 1 details circuit operation driving four 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 SW1 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 4 LEDs 200ns/DIV 3498 F01 Figure 1. Switching Waveforms with Four White LEDs at 2mA Load 3498f 8 LT3498 OPERATION—OLED DRIVER The low noise boost of the LT3498 uses a novel control scheme to provide high efficiency over a wide range of output current. In addition, this technique keeps the switching frequency above the audio band over all load conditions. The operation of the part can be better understood by referring to the Block Diagram. The part senses the output voltage by monitoring the voltage on the FB2 pin. The user sets the desired output voltage by choosing the value of the external topside feedback resistor. The part incorporates a precision 182kΩ bottom-side feedback resistor. Assuming that output voltage adjustment is not used (CTRL2 pin is tied to 1.5V, or greater), the internal reference (VREF = 1.215V) sets the voltage to which FB2 will servo during regulation. The Switch Control block senses the output of the amplifier and adjusts the switching frequency, as well as other parameters to achieve regulation. During the start-up of the circuit, special precautions are taken to ensure that the inductor current remains under control. Because the switching frequency is never allowed to fall below approximately 50kHz, a minimum load must be present to prevent the output voltage from drifting too high. This minimum load is automatically generated within the part via the Shunt Control block. The level of this current is adaptable, removing itself when not needed to improve efficiency at higher load levels. The low-noise boost of the LT3498 also has an integrated Schottky diode and PMOS output disconnect switch. The PMOS switch is turned on when the part is enabled. When the part is in shutdown, the PMOS switch turns off, allowing the VOUT2 node to go to ground. This type of disconnect function is often required in power supplies. APPLICATIONS INFORMATION— LED DRIVER Inductor Selection A 15µH inductor is recommended for most applications for the LED driver of the LT3498. 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 2. Table 1: Recommended Inductors L (µH) 15 15 10 10 15 15 15 MAX DCR (Ω) 0.58 1.6 0.3 1.2 0.764 0.80 0.86 CURRENT RATING (mA) 300 200 450 225 380 360 680 80 75 70 EFFICIENCY (%) 65 60 55 50 45 0 5 10 LED CURRENT (mA) 15 20 3498 F02 15uH Murata LQH32CN150K53 15uH Murata LQH2MCN150K02 15uH Cooper SD3110-150 15uH Toko D312C 15uH Coilcraft DO3314-153ML PART LQH32CN150K53 LQH2MCN150K02 LQH32CN100K53 LQH2MCN100K02 SD3110-150 1001AS-150M (TYPE D312C) D03314-153ML VENDOR Murata www.murata.com Figure 2. Efficiency Comparison of Different Inductors Capacitor Selection The small size of ceramic capacitors makes them ideal for LT3498 LED driver 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 4.7µF input capacitor and a 1µF output capacitor are sufficient for most applications. 3498f Cooper www.cooperet.com Toko www.toko.com Coilcraft www.coilcraft.com 9 LT3498 APPLICATIONS INFORMATION— LED DRIVER Table 2: Recommended Ceramic Capacitor Manufacturers Taiyo Yuden AVX Murata (800) 368-2496 www.t-yuden.com (803) 448-9411 www.avxcorp.com (714) 852-2001 www.murata.com Inrush Current The LT3498 LED Driver has a built-in Schottky diode. When supply voltage is applied to the VIN pin, an inrush current flows through the inductor and Schottky diode and charges up the CAP1 voltage. The Schottky diode for the LED Driver of the LT3498 can sustain a maximum current of 1A. For low DCR inductors, which are usually the case for this application, the peak inrush current can be simplified as follows: r α= 2 •L ω= IPK = 1 r2 – L • C 4 • L2 VIN – 0.6 ⎛ α π⎞ • exp ⎜ – • ⎟ ⎝ ω 2⎠ L•ω Overvoltage Protection The LED driver of the LT3498 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, VCAP1 is clamped at 27V (typ). The LED driver will then switch at a very low frequency to minimize input current. The VCAP1 and input current during output open-circuit are shown in the Typical Performance Characteristics. Figure 3 shows the transient response when the LEDs are disconnected. IL 200mA/DIV 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) 4.2 4.2 4.2 4.2 r (Ω) 0.58 1.6 0.8 0.739 L (µH) 15 15 15 15 COUT (µF) 1 1 1 1 IP (A) 0.828 0.682 0.794 0.803 VCAP1 10V/DIV LEDs DISCONNECTED AT THIS POINT 500µs/DIV VIN = 3.6V FRONT PAGE APPLICATION CIRCUIT 3498 F03 Figure 3. Transient Response with LEDs Disconnected From Output 3498f 10 LT3498 APPLICATIONS INFORMATION— LED DRIVER Programming LED Current The feedback resistor (RSENSE1) and the sense voltage (VCAP1 – VLED1) control the LED current. The CTRL1 pin controls the sense reference voltage as shown in the Typical Performance Characteristics. For CTRL1 higher than 1.5V, the sense reference is 200mV, which results in full LED current. To have accurate LED current, precision resistors are preferred (1% is recommended). The formula and table for RSENSE selection are shown below. 200mV RSENSE1 = ILED Table 4: RSENSE1 Value Selection for 200mV Sense ILED (mA) 5 10 15 20 RSENSE1 (Ω) 40 20 13.3 10 The LED current can be set by: ILED ≈ ILED ≈ 200mV , when VCTRL1 > 1.5V RSENSE1 VCTRL1 , when VCTRL1 < 1.25V 6.25 • RSENSE1 Feedback voltage variation versus control voltage is given in the Typical Performance Characteristics. 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 4) by a RC network and fed to the CTRL1 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 CTRL1 pin which is 10MΩ (typ). Dimming Control There are three different types of dimming control circuits. The LED current can be set by modulating the CTRL1 pin with a DC voltage, a filtered PWM signal or directly with a PWM signal. Using a DC Voltage For some applications, the preferred method of brightness control is a variable DC voltage to adjust the LED current. The CTRL1 pin voltage can be modulated to set the dimming of the LED string. As the voltage on the CTRL1 pin increases from 0V to 1.5V, the LED current increases from 0 to ILED. As the CTRL1 pin voltage increases beyond 1.5V, it has no effect on the LED current. Figure 4. Dimming Control Using a Filtered PWM Signal R1 100kΩ C1 0.1µF LT3498 CTRL1 3498 F04 PWM 10kHz TYP 3498f 11 LT3498 APPLICATIONS INFORMATION— LED DRIVER 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 “on-time”), 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 5 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 5. A simple logic level Si2304 MOSFET can be used since its source is connected to ground. The PWM signal is applied to the CTRL1 pin of the LT3498 and the gate of the MOSFET. VIN 3V TO 5V L1 15µH CAP1 SW1 COUT1 1µF Q1 Si2304BDS 100k PWM FREQ 5V 0V 3498 F05 The PWM signal should traverse between 0V to 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 / RSENSE1 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 6 shows the PWM dimming waveforms for the circuit in Figure 5. ILED 20mA/DIV IL 200mA/DIV PWM 5V/DIV 2ms/DIV 3498 F06 VIN = 3V 4 LEDs Figure 6. Direct PWM Dimming Waveforms 80 75 VIN = 3.4V 4 LEDs 100Hz = PWM EFFICIENCY (%) RSENSE1 10Ω CIN 1µH 70 65 60 55 VIN SW2 CAP2 VOUT2 LT3498 LED1 CTRL1 GND1 GND2 CTRL2 FB2 50 0 2 4 6 8 10 12 14 16 18 20 LED CURRENT (mA) 3498 F07 Figure 7. PWM Dimming Efficiency Figure 5. Li-Ion to Four White LEDs with Direct PWM Dimming 3498f 12 LT3498 APPLICATIONS INFORMATION— LED DRIVER 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 6 is approximately 40µs for a 3V input voltage. The achievable dimming range for this application and 100Hz PWM frequency can be determined using the following method. Example: f = 100Hz, t SETTLE = 40µ s 1 1 t PERIOD = = = 0 . 01s f 100 0 . 01s t = 250 : 1 Di m Range = PERIOD = t SETTLE 40µ s Min Du ty Cycle = 40 µ s t SETTLE • 100 = • 100 = 0 . 4 % t PERIOD 0 . 01s Duty Cycle Range = 100 % → 0 . 4 % at 100Hz The calculations show that for a 100Hz signal the dimming range is 250:1. In addition, the minimum PWM duty cycle of 0.4% 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 40µs. 10000 PWM FREQ Q1 Si2304BDS 100 100k 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 CTRL1 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 CTRL1 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 down to 125mV. 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 CTRL1 signal can be adjusted to lower amplitudes. VIN 3V TO 5V RSENSE1 10Ω L1 15µH CAP1 SW1 COUT1 1µF CIN 1µH VIN SW2 CAP2 VOUT2 LT3498 LED1 CTRL1 GND1 5V 0V GND2 CTRL2 FB2 3498 F09 PWM DIMMING RANGE 1000 PULSING MAY BE VISIBLE 10 Figure 9. Li-Ion to Four White LEDs with Both PWM Dimming and Analog Dimming 1 10 100 1000 PWM FREQUENCY (Hz) 10000 3498 F08 Figure 8. Dimming Ratio vs Freqeuncy 3498f 13 LT3498 APPLICATIONS INFORMATION— OLED DRIVER Inductor Selection Several recommended inductors that work well with the OLED driver of the LT3498 are listed in Table 5, although there are many other manufacturers and devices that can be used. Consult each manufacturer for more detailed information and for their entire selection of related parts. Many different sizes and shapes are available. Use the equations and recommendations in the next few sections to find the correct inductance value for your design. Table 5: Recommended Inductors L (µH) 10 10 15 15 10 15 MAX DCR (Ω) 0.3 1.2 0.58 1.6 0.505 0.764 CURRENT RATING (mA) VENDOR 450 225 300 200 470 380 Murata www.murata.com Capacitor Selection The small size and low ESR of ceramic capacitors makes them suitable for most OLED Driver 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 4.7µF input capacitor and a 10µF output capacitor are sufficient for most applications for the OLED Driver. Always use a capacitor with a sufficient voltage rating. Many capacitors rated at 10µF, particularly 0805 or 0603 case sizes, have greatly reduced capacitance when bias voltages are applied. Be sure to check actual capacitance at the desired output voltage. Generally a 1206 size capacitor will be adequate. A 0.47µF capacitor placed on the CAP node is recommended to filter the inductor current while the larger 10µF placed on the VOUT node will give excellent transient response and stability. Table 6 shows a list of several capacitor manufacturers. Consult the manufacturers for more detailed information and for their entire selection of related parts. Table 6. Recommended Ceramic Capacitor Manufacturers MANUFACTURER Taiyo Yuden AVX Murata Kemet PHONE 408-573-4150 843-448-9411 814-237-1431 408-986-0424 URL www.t-yuden.com www.avxcorp.com www.murata.com www.kemet.com PART LQH32CN100K53 LQH2MCN100K02 LQH32CN150K53 LQH2MCN150K02 SD3110-100 SD3110-150 Cooper www.cooperet.com Inductor Selection—Boost Regulator The formula below calculates the appropriate inductor value to be used for the low noise boost regulator of the LT3498 (or at least provides a good starting point). This value provides a good tradeoff in inductor size and system performance. Pick a standard inductor close to this value. A larger value can be used to slightly increase the available output current, but limit it to around twice the value calculated below, as too large of an inductance will decrease the output voltage ripple without providing much additional output current. A smaller value can be used (especially for systems with output voltages greater than 12V) to give a smaller physical size. Inductance can be calculated as: L = ( VOUT 2 − VIN(MIN) + 0 . 5V) • 0 . 66 (µ H) where VOUT2 is the desired output voltage and VIN(MIN) is the minimum input voltage. Generally, a 10µH or 15µH inductor is a good choice. Setting Output Voltage and the Auxiliary Reference Input The OLED driver of the LT3498 is equipped with both an internal 1.215V reference and an auxiliary reference input. This allows the user to select between using the built-in reference, and supplying an external reference voltage. The voltage at the CTRL2 pin can be adjusted while the chip is operating to alter the output voltage of the LT3498 for purposes such as display dimming or contrast adjustment. To use the internal 1.215V reference, the CTRL2 pin must be held higher than 1.5V. When the CTRL2 pin is held between 0V and 1.5V the OLED driver will regulate the output such that the FB2 pin voltage is nearly equal to the CTRL2 pin voltage. At CTRL2 voltages close to 1.215V, 3498f 14 LT3498 APPLICATIONS INFORMATION— OLED DRIVER a soft transition occurs between the CTRL2 pin and the internal reference. Figure 10 shows this behavior. 1.500 1.250 FB2 VOLTAGE (V) 1.000 0.750 0.500 0.250 Choosing a Feedback Node The single feedback resistor may be connected to the VOUT2 pin or to the CAP2 pin (see Figure 11). Regulating the VOUT2 pin eliminates the output offset resulting from the voltage drop across the output disconnect PMOS. Regulating the CAP2 pin does not compensate for the voltage drop across the output disconnect, resulting in an output voltage VOUT2 that is slightly lower than the voltage set by the resistor divider. Under most conditions, it is advised that the feedback resistor be tied to the VOUT2 pin. Connecting the Load to the CAP2 Node 0 0 0.3 0.5 0.8 1.0 CTRL2 VOLTAGE (V) 1.3 1.5 3498 F10 Figure 10. CTRL2 to FB2 Transfer Curve To set the maximum output voltage, select the values of RFB2 according to the following equation: ⎛V ⎞ RFB2 = 182 • ⎜ OUT2 – 1⎟ , kΩ ⎝ 1.215 ⎠ When CTRL2 is used to override the internal reference, the output voltage can be lowered from the maximum value down to nearly the input voltage level. If the voltage source driving the CTRL2 pin is located at a distance to the LT3498, a small 0.1µF capacitor may be needed to bypass the pin locally. CAP1 SW1 VIN SW2 CAP2 VOUT2 C2 The efficiency of the converter can be improved by connecting the load to the CAP2 pin instead of the VOUT2 pin. The power loss in the PMOS disconnect circuit is then made negligible. By connecting the feedback resistor to the VOUT2 pin, no quiescent current will be consumed in the feedback resistor string during shutdown since the PMOS transistor will be open (see Figure 12). The disadvantage of this method is that the CAP2 node cannot go to ground during shutdown, but will be limited to around a diode drop below VIN . Loads connected to the part should only sink current. Never force external power supplies onto the CAP2 or VOUT2 pins. The larger value output capacitor should be placed on the node to which the load is connected. CAP1 SW1 VIN SW2 CAP2 VOUT2 C3 ILOAD LT3498 LED1 CTRL1 GND1 GND2 CTRL2 FB2 RFB2 LT3498 LED1 CTRL1 GND1 GND2 CTRL2 FB2 3498 F12 RFB2 C2 Figure 12. Improved Efficiency CAP1 SW1 VIN SW2 CAP2 VOUT2 C3 LT3498 LED1 CTRL1 GND1 GND2 CTRL2 FB2 RFB2 3498 F11 Figure 11. Feedback Connection Using the CAP2 Pin or the VOUT2 Pin 3498f 15 LT3498 APPLICATIONS INFORMATION— OLED DRIVER Maximum Output Load Current The maximum output current of a particular LT3498 circuit is a function of several circuit variables. The following method can be helpful in predicting the maximum load current for a given circuit: Step 1: Calculate the peak inductor current: IPK = ILIMIT + VIN • 400 • 10 –9 amps L Step 4: Calculate the nominal output current: IOUT(NOM) = IIN( AVG) • VIN • 0.75 VOUT 2 amps Step 5: Derate output current: IOUT = IOUT(NOM) • 0.7 amps For low output voltages the output current capability will be increased. When using output disconnect (load current taken from VOUT2), these higher currents will cause the drop in the PMOS switch to be higher resulting in reduced output current capability than those predicted by the preceding equations. Inrush Current When VIN is stepped from ground to the operating voltage while the output capacitor is discharged, a higher level of inrush current will flow through the inductor and integrated Schottky diode into the output capacitor. Conditions that increase inrush current include a larger more abrupt voltage step at VIN, a larger output capacitor tied to the CAP2 pin, and an inductor with a low saturation current. While the internal diode is designed to handle such events, the inrush current should not be allowed to exceed 1A. For circuits that use output capacitor values within the recommended range and have input voltages of less than 5V, inrush current remains low, posing no hazard to the device. In cases where there are large steps at VIN (more than 5V) and/or a large capacitor is used at the CAP2 pin, inrush current should be measured to ensure safe operation. where ILIMIT is 0.3A for the OLED driver. L is the inductance value in Henrys and VIN is the input voltage to the boost circuit. Step 2: Calculate the inductor ripple current: IRIPPLE = (VOUT2 + 1 – VIN) • 150 • 10 L –9 amps where VOUT2 is the desired output voltage. If the inductor ripple current is less then the peak current, then the circuit will only operate in discontinuous conduction mode. The inductor value should be increased so that IRIPPLE < IPK. An application circuit can be designed to operate only in discontinuous mode, but the output current capability will be reduced. Step 3: Calculate the average input current: IIN( AVG) = IPK – IRIPPLE amps 2 3498f 16 LT3498 APPLICATIONS INFORMATION— LED AND OLED DRIVER Board Layout Considerations 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 pins (SW1 and SW2). Keep the sense voltage pins (CAP1 and LED1) away from the switching node. The FB2 connection for the feedback resistor RFB2 should be tied directly from the VOUT2 pin to the FB2 pin and be kept as short as possible, ensuring a clean, noise-free connection. Place COUT1 and COUT2 next to the CAP1 and CAP2 pins respectively. Always use a ground plane ender the switching regulator to minimize interplane coupling. Recommended component placement is shown in Figure 13. LED1 RSENSE1 CAP1 C1 SW1 1 CTRL1 2 GND 3 4 CTRL2 5 6 RFB2 VOUT2 FB2 C2 GND VIAS TO GROUND PLANE REQUIRED TO IMPROVE THERMAL PERFORMANCE VIAS TO VOUT2 CAP2 3498 F13 12 11 10 9 8 7 C3 VOUT2 VIN CIN L2 SW2 L1 GND Figure 13. Recommended Board Layout 3498f 17 LT3498 TYPICAL APPLICATIONS Li-Ion to Two White LEDs and OLED/LCD Bias VIN = 3V TO 5V CIN 4.7µF L2 10µH C2 0.47µF C1 1µF L1 10µH 16V 24mA SW2 CAP2 VOUT2 C3 10µF CAP1 SW1 20mA LED1 RSENSE1 10Ω CTRL1 OFF ON SHUTDOWN AND DIMMING CONTROL VIN LT3498 GND1 GND2 CTRL2 OFF ON SHUTDOWN AND CONTROL FB2 RFB2 2.21MΩ 3498 TA02 CIN, C2: X5R OR X7R WITH SUFFICIENT VOLTAGE RATING C1: TAIYO YUDEN GMK212BJ105KG C3: TAIYO YUDEN TMK316BJ106ML L1, L2: MURATA LQH32CN100K53 LED Efficiency VIN = 3.6V, 2 LEDs 75 70 65 EFFICIENCY (%) 60 55 50 45 40 0 5 10 LED CURRENT (mA) 3498 TA02b 15 20 3498f 18 LT3498 TYPICAL APPLICATIONS Li-Ion to Two White LEDs and OLED/LCD Bias VIN = 3V TO 5V CIN 4.7µF L2 10µH C2 0.47µF L1 10µH 16V 24mA SW2 CAP2 VOUT2 C3 10µF C1 1µF CAP1 SW1 VIN LT3498 RSENSE1 10Ω LED1 CTRL1 OFF ON SHUTDOWN AND DIMMING CONTROL GND1 GND2 CTRL2 OFF ON SHUTDOWN AND CONTROL FB2 RFB2 2.21MΩ 20mA 3498 TA03 CIN, C2: X5R OR X7R WITH SUFFICIENT VOLTAGE RATING C1: TAIYO YUDEN GMK212BJ105KG C3: TAIYO YUDEN TMK316BJ106ML L1, L2: MURATA LQH32CN100K53 LED Efficiency VIN = 3.6V, 2 LEDs 80 75 70 EFFICIENCY (%) 65 60 55 50 45 40 0 5 10 LED CURRENT (mA) 3498 TA03b 15 20 3498f 19 LT3498 TYPICAL APPLICATIONS Li-Ion to Three White LEDs and OLED/LCD Bias VIN = 3V TO 5V CIN 4.7µF L2 10µH C2 0.47µF L1 15µH 16V 24mA SW2 CAP2 VOUT2 C3 10µF C1 1µF CAP1 SW1 VIN LT3498 RSENSE1 10Ω LED1 CTRL1 OFF ON SHUTDOWN AND DIMMING CONTROL GND1 GND2 CTRL2 OFF ON SHUTDOWN AND CONTROL FB2 RFB2 2.21MΩ 20mA 3498 TA04 CIN, C2: X5R OR X7R WITH SUFFICIENT VOLTAGE RATING C1: TAIYO YUDEN GMK212BJ105KG C3: TAIYO YUDEN TMK316BJ106ML L1: MURATA LQH32CN150K53 L2: MURATA LQH32CN100K53 LED Efficiency VIN = 3.6V, 3 LEDs 80 75 70 EFFICIENCY (%) 65 60 55 50 45 0 5 10 LED CURRENT (mA) 15 20 3498 TA04b 3498f 20 LT3498 TYPICAL APPLICATIONS Li-Ion to Four White LEDs and OLED/LCD Bias VIN = 3V TO 5V CIN 4.7µF L2 10µH C2 0.47µF L1 15µH 16V 24mA SW2 CAP2 VOUT2 C3 10µF C1 1µF CAP1 SW1 VIN LT3498 RSENSE1 10Ω LED1 CTRL1 OFF ON SHUTDOWN AND DIMMING CONTROL GND1 GND2 CTRL2 OFF ON SHUTDOWN AND CONTROL FB2 RFB2 2.21MΩ 20mA 3498 TA05 CIN, C2: X5R OR X7R WITH SUFFICIENT VOLTAGE RATING C1: TAIYO YUDEN GMK212BJ105KG C3: TAIYO YUDEN TMK316BJ106ML L1: MURATA LQH32CN150K53 L2: MURATA LQH32CN100K53 LED Efficiency VIN = 3.6V, 4 LEDs 80 75 EFFICIENCY (%) 70 65 60 55 50 0 5 10 LED CURRENT (mA) 15 20 3498 TA05b 3498f 21 LT3498 TYPICAL APPLICATIONS Li-Ion to Six White LEDs and OLED/LCD Bias VIN = 3V TO 5V RSENSE1 10Ω CIN 4.7µF L2 10µH D1 C2 0.47µF L1 15µH 24V 24mA CAP2 VOUT2 C3 10µF CAP1 SW1 C1 1µF LED1 20mA CTRL1 VIN LT3498 GND1 SW2 GND2 CTRL2 FB2 RFB2 2.21MΩ OFF ON SHUTDOWN AND DIMMING CONTROL OFF ON SHUTDOWN AND CONTROL 3498 TA06 CIN, C2: X5R OR X7R WITH SUFFICIENT VOLTAGE RATING C1: TAIYO YUDEN GMK212BJ105KG C3: TAIYO YUDEN TMK316BJ106ML D1: CENTRAL SEMICONDUCTOR CMDSH-3 L1: MURATA LQH32CN150K53 L2: MURATA LQH32CN100K53 LED Efficiency, VIN = 3.6V, 6 LEDs 80 75 EFFICIENCY (%) EFFICIENCY (%) 70 65 60 55 50 80 75 70 65 60 55 50 45 0 5 10 LED CURRENT (mA) 3498 TA06b OLED Efficiency and Power Loss VIN = 3.6V, VOUT2 = 16V 400 350 300 POWER LOSS (mW) 250 200 150 100 50 1 10 0 100 15 20 40 0.1 LOAD CURRENT (mA) LOAD FROM VOUT2 LOAD FROM CAP2 POWER LOSS FROM VOUT2 POWER LOSS FROM CAP2 3498 TA06c 3498f 22 LT3498 PACKAGE DESCRIPTION DDB Package 12-Lead Plastic DFN (3mm × 2mm) (Reference LTC DWG # 05-08-1723 Rev Ø) 0.64 ± 0.05 (2 SIDES) 0.70 ± 0.05 2.55 ± 0.05 1.15 ± 0.05 PACKAGE OUTLINE 0.25 ± 0.05 0.45 BSC 2.39 ± 0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 3.00 ± 0.10 (2 SIDES) R = 0.05 TYP R = 0.115 TYP 7 0.40 ± 0.10 12 PIN 1 BAR TOP MARK (SEE NOTE 6) 2.00 ± 0.10 (2 SIDES) 0.64 ± 0.10 (2 SIDES) 6 0.23 ± 0.05 2.39 ± 0.10 (2 SIDES) BOTTOM VIEW—EXPOSED PAD 1 PIN 1 R = 0.20 OR 0.25 × 45° CHAMFER (DDB12) DFN 0106 REV Ø 0.200 REF 0.75 ± 0.05 0.45 BSC 0 – 0.05 NOTE: 1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE 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 3498f 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. 23 LT3498 TYPICAL APPLICATION Output Voltage Ripple vs Load Current 7 VOUT2 PEAK-TO-PEAK RIPPLE (mV) 6 5 4 3 2 1 0 0.1 VOUT 25 24 23 22 21 20 19 18 10 LOAD CURRENT (mA) 1 100 3498 TA06d RFB2 VALUE REQUIRED (MΩ) 3.57 3.40 3.24 3.09 2.94 2.80 2.67 2.49 2.37 2.21 2.05 MAXIMUM OUTPUT CURRENT AT 3V INPUT (mA) 12.5 13.4 14.4 15.6 16.8 18.1 19.6 21.2 22.5 24.2 26 17 16 15 RELATED PARTS PART NUMBER LT1932 LT1937 LT3463/ LT3463A LT3465/ LT3465A LT3466/ LT3466-1 LT3471 LT3473/ LT3473A LT3491 LT3494/ LT3494A LT3497 LT3591 DESCRIPTION Constant-Current, 1.2MHz, High Efficiency White LED Boost Regulator Constant-Current, 1.2MHz, High Efficiency White LED Boost Regulator Dual Output, Boost/Inverter, 250mA ISW, Constant Off-Time, High Efficiency Step-Up DC/DC Converter with Integrated Schottky Diodes COMMENTS VIN : 1V to 10V; VOUT(MAX) = 34V; IQ = 1.2mA; ISD =