ACT6311 Rev 3, 22-Feb-11 White LED/OLED Step-Up Converter FEATURES GENERAL DESCRIPTION • • • • • • The ACT6311 step-up DC/DC converter is optimized for driving OLEDs or white LEDs. It can provide an output voltage up to 24V. The device is capable of driving up to seven LEDs in series from a Lithium-Ion battery, with inherent current matching and uniform brightness. Adjustable Output Voltage Drives OLEDs or White LEDs 30V High Voltage Switch 1MHz Switching Frequency Tiny Inductors and Capacitors The ACT6311 incorporates a 30V high voltage switch. The device operates at 1MHz and allows the use of few external components. The ACT6311 is available in the tiny SOT23-5 package. Tiny SOT23-5 Package APPLICATIONS • • • • • • OLED Applications Cell Phones Digital Cameras PDAs, Laptops MP3 Players GPS Efficiency vs. Output Current ACT6311-0001 100 Efficiency (%) 80 60 VIN = 3.6V VIN = 3V VIN = 3V VIN = 3.6V 40 20 0 0 5 10 15 20 25 30 35 Output Current (mA) Figure 1. Typical Application Circuit Innovative PowerTM -1- www.active-semi.com Copyright © 2011 Active-Semi, Inc. ACT6311 Rev 3, 22-Feb-11 G Figure 2: Application as White LED Drive ORDERING INFORMATION PART NUMBER TEMPERATURE RANGE PACKAGE PINS TOP MARK PACKING ACT6311UC-T -40°C to 85°C SOT23-5 5 YCXB TAPE & REEL PIN CONFIGURATION SW 1 G 2 FB 3 5 IN 4 SHDN ACT6311 UC SOT23-5 PIN DESCRIPTION PIN NUMBER PIN NAME PIN DESCRIPTION 1 SW Switch Output. Connect this pin to the inductor and the Schottky diode. To reduce EMI, minimize the PCB trace path between this pin and the input bypass capacitor. 2 G Ground. 3 FB Feedback Input. This pin is referenced to 1.24V 4 SHDN 5 IN Innovative PowerTM Shutdown Control. Connect to a logic high to enable the device. Connect to a logic low to disable the device. Never leave the pin unconnected. Supply Input. Bypass to G with a capacitor 1µF capacitor or higher. -2- www.active-semi.com Copyright © 2011 Active-Semi, Inc. ACT6311 Rev 3, 22-Feb-11 ABSOLUTE MAXIMUM RATINGS (Note: Exceeding these limits may damage the device. Exposure to absolute maximum rating conditions for long periods may affect device reliability.) PARAMETER VALUE UNIT IN, SHDN Voltage -0.3 to 6 V SW Voltage -0.3 to 30 V FB Voltage -0.3 to VIN + 0.3 V Maximum Power Dissipation (derate 5mW/°C above TA = 50°C) 0.4 W Junction to Ambient Thermal Resistance (θJA) 190 °C/W -40 to 150 °C 300 °C Operating Junction Temperature Lead Temperature (Soldering, 10 sec) ELECTRICAL CHARACTERISTICS (VIN = VSHDN = 3V, TA = 25°C, unless otherwise specified.) PARAMETER SYMBOL TEST CONDITIONS Input Voltage Range Feedback Voltage MIN TYP 2.5 VFB VIN = 3V 1.18 FB Input Current 1.24 MAX UNIT 5.5 V 1.30 V 50 nA Supply Current SHDN = IN 0.7 1.5 mA Supply Current in Shutdown SHDN = G 0 1 µA 1.2 MHz Switching Frequency fSW 0.8 1 Maximum Duty Cycle DMAX 80 85 % Switch Current Limit ILIM 75% Duty Cycle 320 mA Switch On Voltage ISW = 200mA 350 mV Switch Leakage Current VSW = 20V, SHDN = G SHDN Logic High Threshold 10 1.6 V SHDN Logic Low Threshold SHDN Input Current Innovative PowerTM 0 -3- µA 0.4 V 1 µA www.active-semi.com Copyright © 2011 Active-Semi, Inc. ACT6311 Rev 3, 22-Feb-11 ERROR AMPLIFIER Figure 3. Functional Block Diagram with the output of the error amplifier. If the error comparator output is high, the flip-flop is reset and the power switch turns off. Thus, the peak inductor current level is controlled by the error amplifier output, which is integrated from the difference between FB input and the 1.24V reference point. FUNCTIONAL DESCRIPTION The ACT6311 is a high efficiency step-up DC/DC converter that employs a current-mode, fixed frequency pulse-width modulation (PWM) architecture with excellent line and load regulation. Figure 3 shows the functional block diagram of the IC. The flip-flop is set at the start of each oscillator cycle, and turns on the power switch. During this on time, the switch current level is sensed and added to a ramp signal, and the resulting sum is compared Innovative PowerTM The ACT6311 operates at a constant switching frequency for output current higher than 4mA. If the output current decreases further, the IC will enter frequency modulation mode, resulting in some low frequency ripple. -4- www.active-semi.com Copyright © 2011 Active-Semi, Inc. ACT6311 Rev 3, 22-Feb-11 APPLICATION INFORMATION and determine R2 from the output voltage: Inductor Selection ⎛ V ⎞ R 2 = R 1 ⎜ OUT − 1 ⎟ ⎝ 1 . 24 V ⎠ Table 1: Recommended Inductors PART NUMBER (1) White LED Application CURRENT DCR RATING (Ω) (MA) The LED current is determined by the value of the feedback resistor R1. Because the FB input of the IC is regulated to 1.24V, the LED current is determined by ILED = 1.24V/R1. The value of R1 for different LED currents is shown in Table 3. SUPPLIER CDRH3D16-220 350 0.5 Sumida ELJPC220KF 160 4.0 Panasonic LQH3C220 250 0.7 Murata LEM2520-220 125 5.5 Taiyo Yuden Table 3: R1 Resistor Value Selection ILED (MA) R1 (Ω) 5 246 10 124 12 103.3 Capacitor Selection 15 82.7 The ACT6311 only requires a 1µF input capcitor and a 1µF output capacitor for most applications. Ceramic capacitors are ideal for these applications. For best performance, use X5R and X7R type ceramic capacitors, which possess less degradation in capacitance over voltage and temperature ranges. 20 62 A 22µH inductor is typically used for the ACT6311. The inductor should have low DC resistance (DCR) and losses at 1MHz. See Table 1 for examples of small size inductors. To improve efficiency, resistors R2 and R3 can be connected as shown in Figure 4 to lower the effective feedback voltage. The following are dimming control methods for the ACT6311 series white LED application. Diode Selection 1) PWM Signal Driving SHDN The ACT6311 requires a fast recovery Schottky diode as the rectifier. Select a low forward voltage drop Schottky diode with a forward current (IF) rating of 100mA to 200mA and a sufficient peak repetitive reverse voltage (VRRM). Some suitable Schottkky diodes are listed in Table 2. When a PWM signal is connected to the SHDN pin, the ACT6311 is turned on and off alternately under the control of the PWM signal. The current through the LEDs is either zero or full scale. By changing the duty cycle of the PWM signal (typically 1kHz to 10kHz), a controlled average current is obtained. 2) DC Voltage Control Table 2: Recommended Schottky Diodes PART NUMBER IF(MA) VRRM (V) CMDSH-3 100 30 Central CMDSH2-3 200 30 Central BAT54 200 30 Zetex Figure 5 shows an application in which a DC voltage is used to adjust the LED current. The LED current increases when VDC is lower than VFB and decreases when VDC is higher than VFB. In Figure 5, the LED current range of 15mA to 0mA is controlled by VDC = 0V to 2V. SUPPLIER 3) Filtered PWM Control Figure 6 shows an application using a filtered PWM signal to control dimming. OLED Application 4) Logic Control Figure 1 shows the feedback network necessary to set the output voltage. Select the proper ratio of the two feedback resistors R1 and R2 based on the desired output voltage. Typically choose R1 = 20kΩ Innovative PowerTM A logic signal can be used to adjust the LED current in a discrete step, as shown in Figure 7. -5- www.active-semi.com Copyright © 2011 Active-Semi, Inc. ACT6311 Rev 3, 22-Feb-11 LED1 ACT6311 FB LED2 LED3 R2 R1 LOGIC Figure 4. Current Setting for White LED Application Figure 7. Logic Controlled Dimming Start-up and Inrush Current In order to facilitate quick startup, a soft-start circuit is not incorporated into the ACT6311. When the IC is first turned on with no external soft-start circuit, the peak inrush current is about 400mA. Figure 8 shows an implementation for soft-start. When soft-start and dimming controls are used simultaneously, a low frequency PWM signal (less than 10kHz) or the methods in Figures 5, 6 and 7 should be used. LED1 LED2 ACT6311 FB LED3 R3 R2 33.4k 56k VDC Open-Circuit Protection (White LEDs) R1 62Ω If one of the LEDs is disconnected, the FB voltage drops to zero and the IC switches at maximum duty cycle. This results in a high voltage that may exceed the SW voltage rating. To limit this voltage, use a Zener diode as shown in Figure 9. The Zener voltage must be large than the total forward voltage of the LEDs and the current rating should be higher than 0.1mA. Figure 5. DC Voltage Controlled Dimming LED1 Board Layout To reduce EMI, minimize the area and path length of all traces connected to SW. Use a ground plane under the switching regulator and connect R1 directly to the G pin of the IC. LED2 ACT6311 FB LED3 R4 R3 R2 10k 33.4k C1 0.1µF 56k PWM R1 62Ω Figure 6. Filtered PWM Controlled Dimming Innovative PowerTM -6- www.active-semi.com Copyright © 2011 Active-Semi, Inc. ACT6311 Rev 3, 22-Feb-11 D1 OUTPUT C1 100nF R2 200k ACT6311 FB D2 R3 56k R1 20k Figure 9: Open-Circuit Protection Figure 8: Soft-Start Circuit Innovative PowerTM -7- www.active-semi.com Copyright © 2011 Active-Semi, Inc. ACT6311 Rev 3, 22-Feb-11 TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 1, unless otherwise specified.) Efficiency vs. Output Voltage 70 60 VIN = 3.6V Switching Frequency (MHz) 80 VIN = 3V 50 40 30 20 10 ACT6311-0002 90 Efficiency (%) Switching Frequency vs. Temperature 1.10 ACT6311-0001 100 1.05 1.00 0.95 0.90 0 0 5 10 15 20 25 30 -40 35 -15 FB Voltage (V) Current Limit (mA) ACT6311-0004 1.25 250 300 VIN = 3V 1.20 1.15 1.10 40 50 60 70 80 -40 -15 Load Regulation Output Voltage (V) Output Voltage (V) 12.5 VIN = 3.6V 20 25 30 35 5.5 13.0 12.5 3.0 IOUT = 20mA 3.5 4.0 4.5 Input Voltage (V) Load (mA) Innovative PowerTM 5.0 13.5 12.0 15 85 ACT6311-0006 13.0 10 60 14.0 ACT6311-0005 13.5 5 35 Line Regulation 14.0 0 10 Temperature (°C) Duty Cycle (%) 12.0 85 1.30 ACT6311-0003 400 30 60 FB Voltage vs. Temperature Current Limit vs. Duty Cycle 450 20 35 Temperature (°C) Output Current (mA) 250 10 -8- www.active-semi.com Copyright © 2011 Active-Semi, Inc. ACT6311 Rev 3, 22-Feb-11 TYPICAL PERFORMANCE CHARACTERISTICS CONT’D (Circuit of Figure 1, unless otherwise specified.) Switching Waveform in Discontinuous Mode Startup without Soft Start Circuit Inductor Current 200mA/DIV Inductor Current 100mA/DIV VOUT 200mV/DIV ACT6311-0008 ACT6311-0007 SW 5V/DIV VOUT 5V/DIV VIN = 3V No load VIN = 3.6V ILOAD = 20MA SHDN 1µs/DIV 20µs/DIV Startup with Soft Start Circuit Load Step Response VOUT 1V/DIV VOUT 5V/DIV 20mA Load Step 2mA VIN = 3.6V ILOAD = 20mA Test Circuit Figure 8 SHDN ACT6311-0010 ACT6311-0009 Inductor Current 50mA/DIV VIN = 3.6V VOUT = 13.6V 100µs/DIV 4ms/DIV Line Step Response ACT6311-0011 VOUT = 13.6V IOUT = 10mA VOUT 500mV/DIV 5.5V VIN 3V 100µs/DIV Innovative PowerTM -9- www.active-semi.com Copyright © 2011 Active-Semi, Inc. ACT6311 Rev 3, 22-Feb-11 PACKAGE OUTLINE SOT23-5 PACKAGE OUTLINE AND DIMENSIONS SYMBOL DIMENSION IN MILLIMETERS DIMENSION IN INCHES MIN MAX MIN MAX A - 1.450 - 0.057 A1 0.000 0.150 0.000 0.006 A2 0.900 1.300 0.035 0.051 b 0.300 0.500 0.012 0.020 c 0.080 0.220 0.003 0.009 D 2.900 BSC 0.114 BSC E 1.600 BSC 0.063 BSC E1 2.800 BSC 0.110 BSC e 0.950 BSC 0.037 BSC e1 1.900 BSC 0.075 BSC L 0.60REF 0.024REF L1 0.300 0.600 0.012 0.024 θ 0° 8° 0° 8° Active-Semi, Inc. reserves the right to modify the circuitry or specifications without notice. Users should evaluate each product to make sure that it is suitable for their applications. Active-Semi products are not intended or authorized for use as critical components in life-support devices or systems. Active-Semi, Inc. does not assume any liability arising out of the use of any product or circuit described in this datasheet, nor does it convey any patent license. Active-Semi and its logo are trademarks of Active-Semi, Inc. For more information on this and other products, contact email@example.com or visit http://www.active-semi.com. ® is a registered trademark of Active-Semi. Innovative PowerTM - 10 - www.active-semi.com Copyright © 2011 Active-Semi, Inc.