SC4524DEVB View Datasheet(PDF) - Semtech Corporation

Part Name

Description

MFG CO.

SC4524DEVB

18V 2A Step-Down Switching Regulator

Semtech Corporation 

SC4524D

switching time of the NPN transistor (see Table 4).

Table 4. Typical switching time

Input Voltage

12V

Load Current

1A

2A

12.5ns 15.3ns

W + PBST +InPaQddition, the quiescent current loss is

O

PQ = VIN ⋅ 2mA

(11)

N

⋅

IO

⋅

The

FSW

total

power

loss

of

the

SC4524D

is

therefore

P TOTAL = PC + P SW + PB ST + PQ

(12)

IO

40

Fig.9 The temPCp=erDat⋅uVrCeErSiAsTe⋅oIOf

total power dissipation

the SC4524DPisQth=eVpINro⋅ 2dmucAt of the

(Equation

(12))

and

q

JA

(36oC/W),

⋅ IO

wfohr itchhePisSSOtWhICe=-t812heE⋅rDtmSPa⋅plVaiImNck⋅pIaeOgd⋅eaF.nSWce from junction to ambient

) ⋅ I2O ⋅ R DI1Ct2i5soCnojPutBnSrTcetc=iooDnm⋅tmVeBmeSnTpd⋅ee4rIadO0tutore.oIpnetrhaeteaptphelicSaCti4o5n2s4wDithabhoigvhe

input voltage and high output current, the switching

frequePnDcy=m(1a−y Dn)e⋅eVdDt⋅oIObe reduced to meet the thermal

requirement.

PIND = (1.1 ~ 1.3) ⋅ I2O ⋅ R DC

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, the size of the loop formed by these components

should be minimized. Since the power switch is already

integrated within the SC4524D, 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.

V IN

VOU T

ZL

Figure 9. Heavy lines indicate the critical pulse

current loop. The stray inductance of this

loop should be minimized.

Vin

Cu

15

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