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Data Sheet Rev 2, 7/2006
ACT6311
White LED/OLED Step-Up Converter
FEATURES
Adjustable Output Voltage Drives OLEDs or White LEDs 30V High Voltage Switch 1MHz Switching Frequency Tiny Inductors and Capacitors Tiny SOT23-5 Package
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. 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.
APPLICATIONS
OLED Applications Cell Phones Digital Cameras PDAs, Laptops MP3 Players GPS
3V to 5V IN
L1 22H
D1
C1 1F IN SW
R2 200k OLED
C2 1F
ACT6311
ON SHDN G R1 20k FB
Figure 1. Typical Application Circuit
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ACT6311
3V to 5V IN L1 22H LED1 C1 1F IN SW LED2 LED3 20mA C 2 1F D1
ACT6311
ON SHDN G R1 62 FB
Figure 2. Application as White LED Driver
ORDERING INFORMATION
PART NUMBER ACT6311UC-T TEMPERATURE RANGE -40C to 85C PACKAGE SOT23-5 PINS 5 TOP MARK YCXB PACKING TAPE & REEL
PIN CONFIGURATION
SW G FB 1 2 3 5 IN
ACT6311 UC
4 SHDN
PIN DESCRIPTION
PIN NUMBER 1 2 3 4 5 PIN NAME SW G FB SHDN IN
SOT23-5
PIN DESCRIPTION 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. Ground. Feedback Input. This pin is referenced to 1.24V. 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 1F capacitor or higher.
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ACT6311
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 IN, SHDN Voltage SW Voltage FB Voltage Maximum Power Dissipation (derate 5mW/C above TA = 50C) Junction to Ambient Thermal Resistance (JA) Operating Junction Temperature Lead Temperature (Soldering, 10 sec)
VALUE -0.3 to 6 -0.3 to 30 -0.3 to VIN + 0.3 0.4 190 -40 to 150 300
UNIT V V V W C/W C C
ELECTRICAL CHARACTERISTICS
(VIN = VSHDN = 3V, TA = 25C, unless otherwise specified.)
PARAMETER Input Voltage Range Feedback Voltage FB Input Current Supply Current Supply Current in Shutdown Switching Frequency Maximum Duty Cycle Switch Current Limit Switch On Voltage Switch Leakage Current SHDN Logic High Threshold SHDN Logic Low Threshold SHDN Input Current
SYMBOL VFB
TEST CONDITIONS VIN = 3V SHDN = IN SHDN = G
MIN 2.5 1.18
TYP 1.24 50 0.7 0 1 85 320 350
MAX 5.5 1.30 1.5 1 1.2
fSW DMAX ILIM
0.8 80 75% Duty Cycle ISW = 200mA VSW = 20V, SHDN = G 1.6
10 0.4 1
0
UNIT V V nA mA A MHz % mA mV A V V A
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ACT6311
SW IN OSCILLATOR & RAMP GENERATOR
SHDN
REFERENCE VR EF
FB
-
ERROR AMPLIFIER
+
ERROR COMPARATOR
Figure 3. Functional Block Diagram
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 with the output of
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- +
1.24V
+
S
F /F R
Q
CURRENT SENSE AMPLIFIER
+ -
G
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. The ACT6311 operates at a constant switching frequency for output current higher than 4mA. If the output current decreases further, the IC will enter pulse skipping mode, resulting in some low frequency ripple.
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ACT6311
APPLICATION INFORMATION
INDUCTOR SELECTION
Table 1. Recommended Inductors
WHITE LED APPLICATION
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.
Table 3. R1 Resistor Value Selection
CURRENT RATING (mA) CDRH3D16-220 350 ELJPC220KF 160 LQH3C220 250 LEM2520-220 125 PART NUMBER
DCR () 0.5 4.0 0.7 5.5
SUPPLIER Sumida Panasonic Murata Taiyo Yuden
A 22H 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.
ILED (mA) 5 10 12 15 20
R1 () 246 124 103.3 82.7 62
CAPACITOR SELECTION
The ACT6311 only requires a 1F input capacitor and a 1F 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.
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. 1. PWM Signal Driving SHDN 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 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. 3. Filtered PWM Control Figure 6 shows an application using a filtered PWM signal to control dimming. 4. Logic Control A logic signal can be used to adjust the LED current in a discrete step, as shown in Figure 7.
DIODE SELECTION
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 Schottky diodes are listed in Table 2.
Table 2. Recommended Schottky Diodes
PART NUMBER CMDSH-3 CMDSH2-3 BAT54
IF (mA) 100 200 200
VRRM (V) 30 30 30
SUPPLIER Central Central Zetex
OLED APPLICATION
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 = 20k and determine R2 from the output voltage:
R2=R1
V OUT -1 1.24V
(1)
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ACT6311
LED1 LED2 LED1
ACT6311
FB R2
LED2 LED3
ACT6311
FB
R3 2M R2 1M
LED3
LOGIC R1 10
R1
Figure 7. Logic Controlled Dimming Figure 4. Current Setting for White LED Application
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.
R1 62
LED1
ACT6311
FB R3 VDC 33.4k R2 56k
LED2 LED3
OPEN-CIRCUIT PROTECTION (WHITE LEDS)
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 larger 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
ACT6311
FB R4 PWM 10k 33.4k C1 0.1F 56k R3 R2
LED2 LED3
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.
R 1 62
Figure 6. Filtered PWM Controlled Dimming
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ACT6311
D1 OUTPUT IN C1 100nF R2 200 k D2 ON R3 56k R1 20k 3V to 5V L1 22H LED1 C1 1F IN SW LED2 LED3 R2 13k R1 62 C2 1F D1
ACT6311
FB
D2
ACT6311
SHDN G FB
Figure 8. Soft-Start Circuit Figure 9. Open-Circuit Protection
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ACT6311
TYPICAL PERFORMANCE CHARACTERISTICS
(Circuit of Figure 1, unless otherwise specified.)
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ACT6311
TYPICAL PERFORMANCE CHARACTERISTICS CONT'D
(Circuit of Figure 1, unless otherwise specified.)
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ACT6311
PACKAGE OUTLINE
SOT23-5 PACKAGE OUTLINE AND DIMENSIONS
DIMENSION IN MILLIMETERS MIN MAX 1.050 1.250 0.000 0.100 1.050 1.150 0.300 0.400 0.100 0.200 2.820 3.020 1.500 1.700 2.650 2.950 0.950 TYP 1.800 2.000 0.700 REF 0.300 0.600 0 8 DIMENSION IN INCHES MIN MAX 0.041 0.049 0.000 0.004 0.041 0.045 0.012 0.016 0.004 0.008 0.111 0.119 0.059 0.067 0.104 0.116 0.037 TYP 0.071 0.079 0.028 REF 0.012 0.024 0 8
SYMBOL A A1 A2 b c D E E1 e e1 L L1
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 data sheet, 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 sales@active-semi.com or visit www.active-semi.com. For other inquiries, please send to: 1270 Oakmead Parkway, Suite 310, Sunnyvale, California 94085-4044, USA Active-Semi, Inc. - 10 www.active-semi.com

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