CAT4238_16 Datasheet, PDF (10/12 Pages) ON Semiconductor – High Efficiency 10 LED Boost Converter

CAT4238
Board Layout
The CAT4238 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 25 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 25
corresponds to the current path when the CAT4238 internal
switch is closed. On Figure 26 is shown the current loop,
when the CAT4238 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
CAT4238 allows for direct connection of the capacitors to
ground. The resistor R₁ must be connected directly to the
GND pin of the CAT4238 and not shared with the switching
current loops and any other components.
Figure 25. Closed−switch Current Loop
Figure 26. Open−switch Current Loop
Figure 27. Recommended PCB Layout
www.onsemi.com
10