Operating the Evaluation Boards
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A: OUTPUT RESPONSE: 1V/DIV
B: LOAD CURRENT: I
LOAD
= 1A/DIV
Figure 23. Output Response to 0
∼
∼
5A Transient Load
6
Operating the Evaluation Boards
6.1
Setup
The LM2673S-5_EVAL and LM2679S-5_EVAL evaluation boards come ready to be tested. The only
setup needed is connecting the input voltage to the VIN and GND posts. The output can be taken from the
VOUT post. The other signals of interest, switch output (SW out) and softstart (C_SS) posts, are clearly
marked for use in checking the signal integrity. The softstart post has an ON/OFF input when this feature
is being used.
6.2
Operating Conditions
The input source for the LM267x family of regulators must be 8V or greater for proper setup and
operation. The input voltage range for LM2673S-5_EVAL evaluation board is from 8V to 12V and the
range for LM2679S-5_EVAL is from 14V to 28V. The maximum voltage rating of the LM267x family of
regulators is 40V.
Load can be applied from 0A to the maximum for the design. Higher current above the design current limit
will result in activation of the design current limit circuit. It is advisable to have a minimal load of (at least
10 mA) during startup when the input to output differential voltage is greater than 10V to prevent output
ramping beyond desired value.
6.3
PCB Layout Optimization
As in any switching regulator, layout is very important. Rapidly switching currents associated with wiring
inductance can generate voltage transients which can cause problems. For minimal inductance and
ground loops, the printed circuit traces should be as wide and short as possible on the PCB. For best
results, external components should be located as close to the switcher IC as possible using ground plane
construction or single point grounding.
If open core inductors are used, special care must be taken as to the location and positioning of this
type of inductor. Allowing the inductor flux to intersect sensitive feedback, IC groundpath and C
OUT
wiring
can cause problems.
When using the adjustable version, special care must be taken as to the location of the feedback resistors
and associated wiring. Physically locate both resistors near the IC, and route the wiring away from the
inductor, especially an open core type of inductor.
12
AN-1135 LM267X 3A, 5A Evaluation Boards
SNVA013D – December 2000 – Revised April 2013
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