cat4240 Catalyst Semiconductor, cat4240 Datasheet - Page 11

• Manufacturer Part Number: cat4240
• Description: 6 Watt Boost Led Driver
• Manufacturer: Catalyst Semiconductor

V
BOARD LAYOUT
The CAT4240 is a high-frequency switching regulator.
The traces that carry the high-frequency switching
current have to be carefully laid out on the board in
order to minimize EMI, ripple and noise in general.
The thicker lines on Figure 4 show the switching
current path. All these traces have to be short and
wide enough to minimize the parasitic inductance and
resistance. The loop shown on Figure 4 corresponds
to the current path when the CAT4240 internal switch
is closed. On Figure 5 is shown the current loop, when
the CAT4240 switch is open. Both loop areas should
be as small as possible.
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
IN
C
1
Figure 4. Closed-switch Current Loop
Figure 6. Recommended PCB Layout
SHDN
VIN
L
CAT4240
GND
SW
Switch
Closed
FB
D
C
2
V
OUT
R1
11
V
Capacitor C1 has to be placed as close as possible to
the VIN pin and GND. The capacitor C2 has to be
connected separately to the top LED anode. A ground
plane under the CAT4240 allows for direct connection
of the capacitors to ground. The resistor R1 must be
connected directly to the GND pin of the CAT4240
and not shared with the switching current loops and
any other components.
IN
C
1
SHDN
Figure 5. Open-switch Current Loop
VIN
L
CAT4240
GND
SW
Switch
Open
FB
D
Doc. No. MD-5026 Rev. C
C
2
CAT4240
V
OUT
R1