Datasheet

NCP5005
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
V
out
D1
Load
Q1
Figure 8. Output Current Feedback
V
bat
L1
22 mH
R1
xW
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:
R
1
+
Feedback Threshold
I
out
+
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
V
out
V
bat
NCP5005
L1
22 mH
V
bat
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