FAN5665_08 Datasheet, PDF (13/15 Pages) Fairchild Semiconductor – High-Efficiency, Adaptive Charge Pump 5V Boost

Applications Information (Continued)
LED Driver
The FAN5665 can be configured as an LED driver, as
shown in Figure 41. The constant current is generated
by putting a resistor in series with the LED. The value of
series resistor is dictated by the current through the
LED. The maximum current that the FAN5665 can
deliver is 30mA. The number of parallel branches and
current through LEDs should be chosen according to
the maximum output current.
PCB Layout
The PCB layout should be designed carefully due to the
high switching frequency and corresponding transient
currents. All the external capacitors should be
connected very close to the pins of the IC. A clean
board layout with a good ground plane ensures proper
operation of the device. A PCB recommendation for a
two-layer board is shown in Figure 42. Note that the
bottom layer is a dedicated ground plane.
C_IN
2.2µF
C2
0.22µF
VIN
GND
C2-
C2+
EN
VOUT
C1+
C1-
Enable
C_OUT
2.2µF
C1
0.22µF
V_OUT=5V
R_S
R_S
Figure 41. LED Driver Example Circuit
Figure 42. PCB Layout
© 2007 Fairchild Semiconductor Corporation
FAN5665 • Rev. 1.0.1
13
www.fairchildsemi.com