Special Notes
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Figure 4. Silkscreen Image of Printed Circuit Board
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Special Notes
The evaluation board was designed primarily for circuit implementation using all surface-mount
components. The small series "trace inductance", particularly from the Switch Output pin, can create a
high frequency (10's of MHz) ringing signal at the switch output. If problematic, this ringing can be reduced
or eliminated by the use of a series RC damper or snubber network from the switch output to ground. The
addition of these components is made at the locations labeled CD and RD. Values of 0.01 µF and 10
Ω
are
good starting values that may need to be varied depending on the magnitude of parasitic factors in a given
design. In an actual end application, these components are normally not required if proper care to
minimize trace lengths is taken in the PCB design.
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Example Circuit Designs
Example 1: 5V/3A Converter with Surface Mount Components.
In this example, it is desired to convert a voltage range of between 8V and 12V, to 5VDC with load current
of 3A. It is also desired to implement the design with surface mount components only. Softstart duration
will be set to between 1 and 1.5 ms.
Table 3. Target Design Specifications
V
IN
min.
8V
V
IN
max.
16V
V
OUT
5V
I
LOAD
3A
I
CL
5.0A (approx.)
T
SS
1 to 1.5 ms
Table 4. Component Values for an 8-12V in, 5V/3A Out LM2673S-5.0 Buck Converter
Component
Value
Suggested Part Number
U1
Texas Instruments LM2673
CIN
2 x 33 µF/35V
Vishay 594D336X0035R2T
CINX
0.47 µF
Vishay VJ1210U474ZXAA
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AN-1135 LM267X 3A, 5A Evaluation Boards
SNVA013D – December 2000 – Revised April 2013
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