WHITE LED/OLED STEP-UP CONVERTER
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 22µH 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 1µF input capacitor and a 1 µF 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 = 20kΩ 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 I
LED
= 1.24V / R1. The value of R1 for different LED currents is shown in Table 3.
Table 3. R1 Resistor Value Selection
R1 (>)
I
LED
(mA)
5
246
10
124
12
103.3
15
82.7
20
62
3/9
2007-4-24
FOSLINK [ FOSLINK SEMICONDUCTOR CO.,LTD ]
