SC174MLTRT View Datasheet(PDF) - Semtech Corporation
Part Name
Description
MFG CO.
SC174MLTRT
Semtech Corporation
'SC174MLTRT' PDF : 27 Pages View PDF
Layout Guideline
VIN+
VIN-
VO+
VO-
C11
C1
C4 C3 C2
0
L1
R3
C7
R6
0
C5
0
R1
SC174
U1
11 BST
VDD 1100
2 2 VIN
AGND 99
3 3 LX
8
TON
4 4 PGND EN/PSV 77
5 5 PGOOD
FB 66
R7
0
SC174
C10
C6
R2
EN/PSV
R4
C8
C9
0
Schematic for layout illustration
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.
© 2010 Semtech Corporation
20
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