SC4525ASETRT datasheet(15/19 Pages) SEMTECH

15 / 19 page

PCB Layout Considerations

In a step-down switching regulator, the input bypass

capacitor, the main power switch and the freewheeling

diode carry pulse current (Figure 9). For jitter-free

operation,thesizeoftheloopformedbythesecomponents

should be minimized. Since the power switch is already

integrated within the SC4525A, connecting the anode of

the freewheeling diode close to the negative terminal of

the input bypass capacitor minimizes size of the switched

current loop. The input bypass capacitor should be placed

close to the IN pin. Shortening 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.

The exposed pad should be soldered to a large ground

plane as the ground copper acts as a heat sink for the

device. To ensure proper adhesion to the ground plane,

avoid using vias directly under the device.

Figure 9. Heavy lines indicate the critical pulse

current loop. The inductance of this

loop should be minimized.

Vout

Vin

Currents in Power Section

OUT

Vout

Vin

Currents in Power Section

OUT

SC4525A

Applications Information (Cont.)

SC4525ASETRT Arkusz danych(PDF) 15 Page - Semtech Corporation