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WHITE LED/OLED STEP-UP CONVERTER
FSP3304
FEATURES
Adjustable Output Voltage Drives OLEDs or White LEDs 30V High Voltage Switch 1 MHz Switching Frequency Tiny Inductors and Capacitors Tiny SOT23-5L Package
GENERAL DESCRIPTION
The FSP3304 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 FSP3304 incorporates a 30V high voltage switch. The device operates at 1 MHz and allows the use of few external components. The FSP3304 is available in the tiny SOT23-5L package.
APPLICATIONS
OLED Applications Cell Phones Digital Cameras PDAs, Laptops MP3 Players GPS
PIN CONFIGURATION
(Top View)
Symbol 1 2 3 4 5
Name SW G FB SHDN IN
Descriptions 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 of 1 F or higher.
TYPICAL APPLICATION CIRCUIT
(1) Application as OLED driver
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(2) Application as White LED driver
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WHITE LED/OLED STEP-UP CONVERTER
FSP3304
ABSOLUTE MAXIMUM RATINGS (NOTE )
Parameter SW voltage IN, SHDN voltage FB voltage Maximum power dissipation (derate 5mW/ above TA=50) Operating temperature range Operating junction temperature Junction to ambient thermal resistor Lead temperature (Soldering, 10sec) Note : Exceeding these ratings may damage the device. Rating -0.3to +30 -0.3 to +6 -0.3 to VIN + 0.3 0.4 -40 to +85 -40 to +150 190 300 Unit V V W /W
ELECTRICAL CHARACTERISTICS
(VIN = VSHUT, TA = 25C, unless otherwise noted.) Parameters Symbol Input Voltage Range Supply Current Supply Current in shutdown Switching Frequency Maximum Duty Cycle SHDN SHDN logic high threshold SHDN logic low threshold SHDN input current Feedback FB Voltage FB Input Current Output Switch SW On voltage SW Current Limit Switch leakage current IL M VFB VI N = 3V 1.18 1.24 50 350 320 10 1.30 V nA
mV
Condition SHDN=IN SHDN=G
Min 2.5
Typ 0.7 0 1 85
Max 5..5 1.5 1 1.2
Units V mA A MHz % V V uA
fSW DMAX
0.8 80 1.6
0
0.4 1
ISW =200mA Duty Cycle =70% VSW=20V, SHDN=G
mA A
FUNCTIONAL BLOCK DIAGRAM
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FSP3304
FUNCTION DESCRIPTION
The FSP3304 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. 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 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 FSP3304 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.
APPLICATION INFORMATION
Inductor Selection Table 1. Recommended Inductors Part Number CDRH3D16-220 ELJPC220KF LQH3C220 LEM2520-220 Current Rating (mA) 350 160 250 125 DCR(>) 0.5 4.0 0.7 5.5 Supplier Sumida Panasonic Murata Taiyo Yuden
A 22H inductor is typically used for the FSP3304. The inductor should have low DC resistance (DCR) and losses at 1 MHz. See Table 1 for examples of small size inductors. Capacitor Selection The FSP3304 only requires a 1F input capacitor and a 1 F 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. Diode Selection The FSP3304 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:
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 R1 (>) ILED (mA) 5 246 10 124 12 103.3 15 82.7 20 62
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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 FSP3304 series white LED application. 1. PWM Signal Driving SHDN When a PWM signal is connected to the SHDN pin, the FSP3304 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 1 kHz 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.
FSP3304
Figure 4: Current setting for white LED application
Figure 5: DC voltage controlled dimming
Figure 6: Filtered PWM controlled dimming
Figure 7: Logic controlled dimming
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FSP3304
Start-up and Inrush current In order to facilitate quick startup, a soft-start circuit is not incorporated into the FSP3304. 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. 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 0.1 mA. 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.
Figure 8: Soft-start circuit
Figure 9: Open-circuit protection
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FSP3304
TYPICAL PERFORMANCE CHARACTERISTICS
(circuit of figure 1, unless otherwise noted)
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FSP3304
TYPICAL PERFORMANCE CHARACTERISTICS (CONTINUED)
(circuit of figure 1, unless otherwise noted)
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FSP3304
ORDERING INFORMATION
FSP3304X X X
Package: C: SOT23-5L
Packing: A: Tape & Reel
Temperature Grade: D: -40~85
Marking Information
LCYM
Date Code: Y: Year (1=2001) M: Month (1~9,O,N,D) Part Number: FSP3304
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FSP3304
PACKAGE INFORMATION
D
e1
5
4
E1 E
A2 A
e
b
C L L1
Symbol A A1 A2 b C D E E1 L L1 e e1
Dimensions 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 2.650 2.950 1.500 1.700 0.300 0.600 0.700REF 0.95 Bsc. 1.90 Bsc. 0 8
Dimensions In Inches Min. Max. 0.041 0.050 0.000 0.004 0.041 0.045 0.012 0.016 0.004 0.008 0.111 0.119 0.104 0.116 0.060 0.068 0.012 0.024 0.028REF 0.038 Bsc. 0.076 Bsc. 0 8
A1
1
2
3
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