NCP5006

http://onsemi.com

8

Output Current Range Set−Up

The current regulation is achieved by means of an external sense resistor connected in series with the LED string.

CONTROLLER

GND

3

FB

GND

1

D1

Q1

Figure 8. Output Current Feedback

L1

22

mH

R1

x

W

The current flowing through the LED creates a voltage

drop across the sense resistor R1. The voltage drop is

constantly monitored internally, and maximum peak

current allowed in the inductor is set accordingly in order

to keep constant this voltage drop (and thus the current

flowing through the LED). For example, should one need

a 10 mA output current, the sense resistor should be sized

according to the following equation:

R1 +

Feedback Threshold

Iout

+ 200 mV

10 mA

+ 20 W

(eq. 9)

A standard 5% tolerance resistor, 22

W SMD device,

yields 9.09 mA, good enough to fulfill the back light

demand. The typical application schematic diagram is

provided in Figure 9.

Figure 9. Basic Schematic Diagram

GND

EN

2

1

5

NCP5006

L1

22

mH

C1

4.7

mF

GND

D6

D5

D4

D3

U1

4

D2

GND

3

GND

R1

22

W

D1

MBR0530

GND

C2

1.0

mF

FB

Pulse

LWT67C LWT67C LWT67C LWT67C LWT67C