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SC443
Applications Information (continued)
Output Rectifying Diode Selection
Schottky diodes are the ideal choice for SC443 due to their
low forward voltage drop and fast switching speed. Table
4 shows several different Schottky diodes that work well
with the SC443. Make sure that the diode has a voltage
rating greater that the possible maximum ouput volt-
age. The diode conducts current only when the power
switch is turned off. A diode of 1A will be sufficient for
most designs.
Layout Guidelines
The SC443 contains a boost converter and the placements
of the power components outside. The SC443 should fol-
low the layout guidelines of a general boost converter.
The application circuit on page 16 will be used as an
example. The layout illustration diagram is shown on
page 16. R5 and C7 form a decoupling filter for the SC443.
C7 should be placed as close as possible to the VIN and
PGND to achieve the best performance. C6 is the input
power filtering capacitor for the boost converter power
train. L1 is the boost converter input inductor. D1 is the
output rectifying diode and it is recommended that a
Schottky diode be used for fast reverse recovery.
To minimize switching noise for the boost converter, the
output capacitor, C3, should be placed at the bottom, as
displayed on page 17, so that the loop formed by C6, D1,
and the internal switch, is the smallest. The output of the
boost converter is used to power up the LEDs. R6 and C9
form the compensation network for the boost converter.
C9 should return to analog ground.
Table 4. Recommended Rectifying Diodes
Since there is pad at the bottom of the SC443 for heat
dissipation, a copper area right underneath the pad is
used for better heat spreading. On the bottom layer of
the board another copper area connected through vias
to the top layer, is used for better thermal performance.
The pad at the bottom of the SC443 should be tied to
the analog ground. The analog ground should be con-
nected to the power ground at one point for better noise
immunity.
Part
SS13
SS14
Vendor
Vishay
www.vishay.com
C8 determines the soft-start time and should be con-
nected to analog ground. R8 is the output current pro-
gramming resistor for IO1 through IO3 and should return
to analog ground. IOGND should also be connected to
AGND.
? 2009 Semtech Corp.
www.semtech.com 15
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