CAT4137 Datasheet, PDF (14/16 Pages) Catalyst Semiconductor – CMOS Boost Converter - White LED Driver

CAT4137
Board Layout
The CAT4137 is a high-frequency switching regulator.
Traces carrying high-frequency switching current have to be
carefully layout on the board in order to minimize EMI,
ripple and noise in general. The thicker lines shown on
Figure 34 indicate 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 34 corresponds to the current path when the
CAT4137 internal switch is closed. On Figure 35 is shown
the current loop when the CAT4137 switch is open. Both
loop areas should be as small as possible.
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
CAT4137 allows for direct connection of the capacitors to
ground. The resistor R1 must be connected directly to the
GND pin of the CAT4137 and not shared with the switching
current loops and any other components.
L
V_IN
D
V_OUT
L
V_IN
D
V_OUT
SW
VIN
SW
VIN
SHDN
CAT4137
Switch
Closed
FB
SHDN
CAT4137
Switch
Open
FB
C₁
C₂
R1 C1
C₂
R1
GND
GND
Figure 34. Closed−switch Current Loop
Figure 35. Open−switch Current Loop
http://onsemi.com
14