CAT4137TD-T3 Datasheet, PDF (13/16 Pages) ON 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 4 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 4 corresponds to the current
path when the CAT4137 internal switch is closed. On
Figure 5 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
SW
VIN
VIN
SHDN
CAT4137 ^Switch
Closed
FB
SHDN
CAT4137
Switch
Open
FB
C₁
C₂
R1
C₁
C₂
R1
GND
GND
Figure 4. Closed-switch current loop
Figure 5. Open-switch current loop
© 2008 SCILLC. All rights reserved.
13
Characteristics subject to change without notice
Doc. No. MD-5012 Rev. C