2007. 2. 26

4/7

KAB3403T/DN

Revision No : 0

Inductor Section

A 10uH inductor is sufficient for most application. The efficiency

comparision of different value inductors help you design your

application circuits.

Inductor Section

A 1uF input capacitor and output capacitor above 1uF are

sufficient for most KAB3403T/DN application.

Diode Selection

For Diode Selection, both forward voltage drop and diode

capacitance need to be considered. Schottky diodes with higher

current ratings usually have lower forward voltage and larger diode

capacitance, which can cause significant switching losses. A

schottky diode rated at 100mA to 200mA is sufficient for most

KAB3403T/DN applications.

LED Current Control

The LED current is controlled by the feedback resistor (RSENSE

in Figure 1). The feedback reference is 320mV. The LED current

is 320mV/RSENSE . The tolerance of LED Current is depends on

tolerance of RSENSE and feedback reference.

Open-Circuits Protection

In the case of output open circuit, when LEDs are disconnected

from the circuit or the LEDs fail, the feedback voltage will be zero.

The KAB3403T/DN will then switch at a high duty cycle resulting

in a high output voltage. But Internal Over Voltage Protection

Circuits prevent output voltage ascending over OVD pin

voltage(19V ~ 23V see Fig 4). This circuits is valid when driving

up to 4 LEDs in series. But, when driving more than 4 LEDs in

series, Normal output voltage could be over OVD pin voltage. In

this case, zener diode can be used to check connect of OVD pin to

LED anode.(see Fig 5) [Recommended Zener diode : KDZ3.0V]

Dimming Control

There are 4 different type of dimming control circuits;

1. Using a DC Voltage to CTL pin

Part No.

Reverse

Voltage (V)

Forward

Current (mA)

Voltage

Drop (V)

Package

KDR730E

30

200 mA

0.6V (max)

at 200 mA

1.60

1.20

KDR720E

30

200 mA

0.5V(max)

at 200 mA

1.60

1.20

KDR412

20

500 mA

0.5V(max)

at 500 mA

1.70

2.50

LOAD CURRENT (mA)

10

74

70

64

60

82

86

90

72

78

76

68

66

62

80

84

88

05

30

15

35

20

25

4.7

µH

10

µH

V

L1

4.7

µH ~ 22µH

SW

C1

1

µF

C2

1

µF

D1

CTL

FB

OVD

LED1

LED2

LED3

LED4

GND

R1

16

Ω

GND

SW

C1

C2

R1

16

Ω

D1

CTL

FB

OVD

L1

4.7

µH~22µH

1

µF

1

µF

LED1

LED2

LED3

LED4

LED5

LED6

KAB3403T/DN

KAB3403T/DN

Figure4. 4LEDs driver with Open-circuit protection.

Figure5. 6LEDs driver with Open-circuit protection.

Figure3. Efficiency Comparison of different value inductors

Table1. Recommended Schottky Diode

Description

UNIT

Rate Of the LED Current

0

25 ~ 100

100

%

0

5 ~ 20

20

mA