SC2440AEVB datasheet(23/28 Pages) SEMTECH

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Applications Information (Continued)

necting the anodes of both freewheeling diodes close to

the negative terminal of the input bypass capacitor mini-

mizes size of the switched current loop. The input bypass

capacitors should be placed close to the IN pins. Short-

ening the traces of the SW and BST nodes reduces the

parasitic trace inductance at these nodes. This not only

reduces EMI but also decreases switching voltage spikes

at these nodes.

Figure 4 shows an example of external component

placement around the SC2440A. The input bypass capaci-

tor C

5, the output filtering capacitors and the freewheel-

ing diodes are grounded on the power ground plane. The

feedback resistor dividers, the compensation networks

and the soft-start capacitors are to be tied to analog

ground. The frequency-setting resistor R

9 is placed next to

the ROSC pin and is also connected to analog ground.

The exposed pad should be soldered to a large power

ground plane as the ground copper acts as a heat sink

for the device. To ensure proper adhesion to the ground

plane, avoid using large vias directly under the device. In

Figure 4(a) two 2mil vias are placed at the edge of the

underside pad.

SC2440A

Suggested PCB Layout for the SC2440A (a) Top Layer and (b) Bottom Layer

Figure 14.

(a)

(b)

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