WHITE LED/OLED STEP-UP CONVERTER

FSP3304

2007-4-24

3/9

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

Current Rating (mA)

DCR(>)

Supplier

CDRH3D16-220

350

0.5

Sumida

ELJPC220KF

160

4.0

Panasonic

LQH3C220

250

0.7

Murata

LEM2520-220

125

5.5

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

IF (mA)

VRRM (V)

Supplier

CMDSH-3

100

30

Central

CMDSH2-3

200

30

Central

BAT54

200

30

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

Table 3. R1 Resistor Value Selection

R1 (>)

5

246

10

124

12

103.3

15

82.7

20

62