CAT4137TS datasheet(13/14 Pages) CATALYST

13 / 14 page

CAT4137

Doc. No. MD-5012Rev. B

Characteristics subject to change without notice

BOARD LAYOUT

The CAT4137 is a high-frequency switching regulator.

Traces carrying 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

shown on Figure 4 indicate 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 4 corresponds to the current

path when the CAT4137 internal switch is closed. On

Figure 5 is shown the current loop when the CAT4137

switch is 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 CAT4137 allows for direct

connection of the capacitors to ground. The resistor

R1 must be connected directly to the GND pin of the

CAT4137 and not shared with the switching current

loops and any other components.

Figure 4. Closed-switch current loop

Figure 5. Open-switch current loop

VIN

CAT4137

VIN

VOUT

Switch

Closed

SHDN

GND

VIN

CAT4137

VIN

VOUT

Switch

Open

SHDN

GND

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