NCP5007
Output Current Range Set−Up
The current regulation is achieved by means of an external sense resistor connected in series with the LED string.
V
bat
L1
22 mH
V
out
D1
4
FB
1
Q1
CONTROLLER
GND
R1
xW
GND
Figure 8. Output Current Feedback
Feedback Threshold
200 mV
10 mA
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:
(eq. 9)
R
+
+
+ 20 W
1
I
out
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.
V
bat
U1
3
C1
5
4
Pulse
EN
V
bat
4.7 mF
GND
L1
22 mH
D1
2
1
V
out
GND
GND
FB
MBR0530
C2
1.0 mF
NCP5007
D6
D5
D4
D3
D2
R1
GND
GND
22 W
LED
LED
LED
LED
LED
Figure 9. Basic Schematic Diagram
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