CAT4237 Datasheet, PDF (11/13 Pages) Catalyst Semiconductor – High Voltage CMOS Boost White LED Driver

BOARD LAYOUT
The CAT4237 is a high-frequency switching
regulator. The traces that carry the 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 on Figure 3 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 3 corresponds to the
current path when the CAT4237 internal
switch is closed. On Figure 4 is shown the
current loop, when the CAT4237 switch is
Figure 3. Closed-switch current loop
CAT4237
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 CAT4237 allows for direct connection of
the capacitors to ground. The resistor R1
must be connected directly to the GND pin of
the CAT4237 and not shared with the
switching current loops and any other
components.
Figure 4. Open-switch current loop
closed
open
© 2005 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
11 of 13
Doc. No. 5013, Rev. A