SC174 datasheet(20/27 Pages) SEMTECH

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Layout Guideline

Since the SC174 has integrated switches, special consid-

eration should be given to board layout. Let us use the

schematic shown above as an example. The board level

layout is illustrated in the following four layers.

As shown on the top layer layout, U1 is the switching

regulator SC174. C1 and C11 serve as the decoupling ca-

pacitor for the buck converter power train. C11, with a

value between 1nF and 10nF, is the high frequency fil-

tering capacitor. It is recommended to put C1 and C11

as close as possible to the SC174 to get the best decou-

pling performance, with C11 closest. L1 is the output

filtering inductor. C2, C3 and C4 are the output filtering

capacitors. C5 is the boostrap capacitor. Pin 10 (VDD) is

the input bias power for the internal circuits. It is recom-

mended to get the power from VIN through an RC filter-

ing network consisted of R1, C6 and C10. The value of R1

can be between 3.01W and 10W and the capacitance of

C10 should be above 1mF. C6, with a value of 1nF, is the

high frequency filtering capacitor. The locations of C6

and C10 should be as close as possible to pins 9 and 10,

with C6 closest, to get the best possible filtering result.

R2 is the on-time programming resistor. R2 should be

located as close as possible to pin 8 and it should return

to analog ground. The EN/PSV pin is a tri-state pin. Pull

EN/PSV high to enable the part with power save mode

enabled. Connect EN/PSV to AGND to disable the switch-

ing regulator. Leave EN/PSV floating to enable the IC in

forced continuous conduction mode.

Since there are two integrated MOSFETs inside the SC174

that will dissipate a lot of power, to help spread the heat

out of the IC more efficiently, there is a thermal pad un-

derneath the SC174 serving as a heat sink. To enlarge the

heat sinking area, a large copper plane under the thermal

pad as shown on the top layer is recommended.

On inner layer 2, a large analog ground plane (AGND) on

the right hand side is connected to the thermal pad un-

derneath the SC174 using vias. Thus the heat generated

inside the SC174 can be spread through the vias to the

inner layers to expand the heat sinking area.

BST

VIN

PGND EN/PSV

TON

AGND

VDD

PGOOD

EN/PSV

VIN+

VIN-

VO+

VO-

SC174

C10

C11

Schematic for layout illustration

SC174

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