CAT4237TD-T3 Datasheet, PDF (11/14 Pages) ON Semiconductor – High Voltage CMOS Boost White LED Driver

CAT4237
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 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 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.
closed
Figure 3. Closed-switch Current Loop
open
Figure 4. Open-switch Current Loop
2008 SCILLC. All rights reserved.
11
Characteristics subject to change without notice
Doc. No. MD-5013, Rev. C