EVAL-ADP1864_15 Datasheet, PDF (4/16 Pages) Analog Devices – Evaluation Board for ADP1864 with Web Design Tool

EVAL-ADP1864
MEASURING THE PERFORMANCE OF THE EVALUATION BOARD
MEASURING OUTPUT VOLTAGE RIPPLE
MEASURING THE INDUCTOR CURRENT
To observe the output voltage ripple, place an oscilloscope
across the output capacitor (COUT) 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 μs/division time base. For a more accurate
measurement, the test leads should be as short as possible, as
shown 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 anode of the diode, which is on the GND plane.
Set the scope to dc coupling, 2 V/division, and 2 μs/division
time base. The switching waveform should alternate between
the negative forward voltage drop of the diode and approx-
imately the input voltage with resonances near the switching
transitions.
MEASURING THE GATE-TO-SOURCE WAVEFORM
To observe the gate-to-source waveform, place an oscilloscope
probe at TP7 with the ground lead at the test point nearest to
the anode of the diode, 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 anode of the diode.
Use 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. For a more accurate measurement, the test leads should be
as short as possible, as shown in Figure 3.
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 the
following equation:
n = ^{VOUT × I OUT}
V_IN × I _IN
Sweep the load across the full load range to obtain the 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.
Figure 3. Measuring Technique for Output Voltage Ripple
Rev. C | Page 4 of 16