CAT4201TD-GT3 Datasheet, PDF (12/15 Pages) ON Semiconductor – 350mA High Efficiency Step Down LED Driver

CAT4201
Open LED Behavior
If the LEDs are not connected, the CAT4201 stops
switching and draws very little current.
At power-up with no load connected, the capacitor C2
is charged-up by the CAT4201. As soon as the bottom
side of the capacitor (C2-) reaches 0 volt, as shown
on Figure 10, the CAT4201 stops switching and
remains in the idle mode only drawing about 0.4mA
current from the supply.
Board Layout
In order to minimize EMI and switching noise, the
Schottky diode, the inductor and the output capacitor
C2 should all be located close to the driver IC. The
input capacitor C1 should be located close to the
VBAT pin and the Schottky diode cathode. The
CAT4201 ground pin should be connected directly to
the ground plane on the PCB. A recommended PCB
layout with component location is shown on Figure 11.
The LEDs are connected by two wires tied to both
sides of the output capacitor C2. The LEDs can be
located away from the driver if needed.
Figure 10. Open LED mode
Figure 11. Recommended PCB Layout
In order to further reduce the ripple on the supply rail,
an optional Pi style filter (C-L-C) can be used. A 10µH
inductor rated to the maximum supply current can be
used.
Doc. No. MD-5025 Rev. E
12
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Characteristics subject to change without notice