SC173AMLTRT View Datasheet(PDF) - Semtech Corporation
Part Name
Description
MFG CO.
SC173AMLTRT
Semtech Corporation
'SC173AMLTRT' PDF : 26 Pages View PDF
Layout Guideline
VIN+
C11
C1
VIN-
VO+
VO-
C4 C3 C2
0
L1
R3
C7
R6
0
C5
0
R1
SC173A
U1
1 BST
VDD 10
2 VIN
3 LX
AGND 9
8
TON
4 PGND
EN 7
5 PGOOD
FB 6
R7
0
SC173A
C10
C6
R2
Enable
R4
C8
C9
0
Schematic for layout illustration
Since the SC173A has integrated switches, special con-
sideration 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 SC173A. C1 and C11 serve as the decoupling
capacitor for the buck converter power train. C11, with a
value between 1nF and 10nF, is the high frequency filter-
ing capacitor. It is recommended to put C1 and C11 as
close as possible to the SC173A to get the best decou-
pling performance, with C11 closest. C1, with a value of
10uF, should be placed no more than 3mm away from
the VIN pin. 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 recommended to get the power
from VIN through an RC filtering 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 ca-
© 2010 Semtech Corporation
pacitor. 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. Pull EN high
(above 1V) or permit it to float to enable the part with
automatic power save enabled. Connect EN to AGND to
disable the switching regulator.
Since there are two integrated MOSFETs inside the
SC173A that will dissipate a lot of power, to help spread
the heat out of the IC more efficiently, there is a thermal
pad underneath the SC173A serving as a heat sink. To
enlarge the heat sinking area, a large copper plane un-
der the thermal pad as shown on the top layer is recom-
mended.
On inner layer 2, a large analog ground plane (AGND) on
the right hand side is connected to the thermal pad un-
derneath the SC173A using vias. Thus the heat generated
inside the SC173A can be spread through the vias to the
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