CAT4201_15 Datasheet, PDF (11/12 Pages) ON Semiconductor – High Efficiency Step Down LED Driver

CAT4201
VIN R5
1W
C1
4.7 μF
U1
VBAT
CAT4201
R1 _{8.3 kΩ} ^RSET
CTRL SW
GND
D1
L1
22 μH
C4
10 μF
1A
R4
1 kΩ
C2
4.7 μF
U2
VBAT
CAT4201
R2
RSET
8.3 kΩ
CTRL SW
GND
D2
L2
22 μH
C3
4.7 μF
R3
8.3 kΩ
U3
VBAT
CAT4201
RSET
CTRL SW
GND
D3
L3
22 μH
Figure 31. Open LED Mode
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 32. 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 30. Three CAT4201 in Parallel for 1 A LED
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 31,
the CAT4201 stops switching and remains in the idle mode
only drawing about 0.4 mA current from the supply.
Figure 32. 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 10 mH
inductor rated to the maximum supply current can be used.
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