Datasheet

ADP1864-EVALZ
Rev. A | Page 4 of 12
MEASURING THE PERFORMANCE OF THE EVALUATION BOARD
MEASURING OUTPUT VOLTAGE RIPPLE
To observe the output voltage ripple, place an oscilloscope
across the output capacitor (C
OUT
) with the probe ground lead at
the negative (−) capacitor terminal and the probe tip at the
positive (+) capacitor terminal. Set the oscilloscope to ac-
coupled, 100 mV/division, and 2 s/division time base. For a
more accurate measurement, the test leads should be as short as
possible, as seen in
Figure 3. The output ripple voltage increases
as the input voltage is increased because the duty cycle is
decreased.
MEASURING THE SWITCHING WAVEFORM
To observe the switching waveform with an oscilloscope, place
the oscilloscope probe tip to TP6 with the probe ground at test
point near the diode’s anode, which is on the GND plane. Set
the scope to dc coupling, 2 V/division, and 2 s/division time
base. The switching waveform should alternate between the
negative forward voltage drop of the diode and approximately
the input voltage with resonances near the switching transitions.
MEASURING THE GATE-SOURCE WAVEFORM
To observe the gate-source waveform, place an oscilloscope
probe at TP7 with the ground lead at the test point nearest to
the diode’s anode, which is on the GND plane. Place another
oscilloscope probe at the source of the MOSFET with the
ground lead at the test point nearest the diode’s anode. Utilize
the math functions of the oscilloscope to observe the gate to
source waveform. Do not place a probe across gate to source
terminals of the MOSFET unless a differential probe is being
used. Once again, for a more accurate measurement, the test
leads should be as short as possible, as seen in
Figure 3.
MEASURING THE INDUCTOR CURRENT
The inductor current can be measured by removing one end of
the inductor from its pad and connecting a wire with adequate
current handling capabilities from the pad to inductor lead.
Then, a current probe can be used to measure the current
through the inductor, as shown in
Figure 2.
MEASURING EFFICIENCY AND LOAD REGULATION
Using the voltages from the voltmeters and current readings
from the source and load, calculate efficiency from
I
N
I
N
OUTOUT
I V
I V
n
×
×
=
Sweep the load across the full load range to obtain efficiency
and load regulation plot.
The efficiency results should correspond to the
ADP1864 Buck
Design Software
.
MEASURING LINE REGULATION
Vary the input voltage and examine the change in the output
voltage reading from the voltmeter.
MONITORING SHORT CIRCUIT BEHAVIOR
Place a current probe on the load cable that connects the output
to the positive input of the electronic load. Monitor the output
voltage with a similar technique used to measure the output
voltage ripple; however, dc couple the scope with a 5 V/div
setting. Many electronic loads have short circuit capability.
Enable this function on the load and ensure that the circuit
current limits at the correct current.
05612-017
Figure 3. Measuring Technique for Switching Waveforms