CAT4240 Datasheet, PDF (10/12 Pages) Catalyst Semiconductor – 6 Watt Boost LED Driver

CAT4240
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 26 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 26 corresponds to the current path when the
CAT4240 internal switch is closed. On Figure 27 is shown
V_IN
L
D
V_OUT
the current loop, when the CAT4240 switch is open. Both
loop areas should be as small as possible.
Capacitor C₁ has to be placed as close as possible to the
V_IN 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.
V_IN
L
D
V_OUT
SW
VIN
SHDN
CAT4240
Switch
Closed
FB
C₁
C₂
GND
SW
VIN
SHDN
CAT4240
Switch
Open
FB
R1 C1
GND
C₂
R1
Figure 26. Closed−switch Current Loop
Figure 27. Open−switch Current Loop
Figure 28. Recommended PCB Layout
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