Measuring Evaluation Board Performance - Analog Devices ADP2442-EVALZ User Manual

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MEASURING EVALUATION BOARD PERFORMANCE

Output Voltage Ripple
To observe the output voltage ripple, place an oscilloscope probe
tip at the T3 terminal and connect the probe ground lead at the
negative (−) the T4 terminal. Set the oscilloscope to an ac-coupled,
100 mV/division and 2 µs/division time base.
Switching Waveform
To observe the switching waveform with an oscilloscope, place
the oscilloscope probe tip at the end of the inductor that is
connected to the SW pin with the probe ground at Terminal T4,
PGND. Set the scope to dc, 5 V/division, and 2 µs/division time
base. Alternate the switching waveform between 0 V and
approximately the input voltage.
Measuring Load Regulation
Measure the load regulation by increasing the load at the output
and looking at the change in the output voltage. To minimize voltage
drop, use short low resistance wires, especially for heavy loads.
Measuring Line Regulation
Vary the input voltage and examine the change in the output
voltage. In PWM mode, ensure that the output voltage ripple is
small (<50 mV); however, in pulse skip mode, the output voltage
ripple can be as large as 100 mV.
Measuring Efficiency
The efficiency, η, is measured by comparing the input power with
the output power.
×
V
η
=
OUT
×
V
IN
Measure the input and output voltages as close as possible to the
input and output capacitors to reduce the effect of IR drops.
Inductor Current
By removing one end of the inductor from its pad and connecting a
current loop in series with it, the inductor current can be measured.
Once this is done, a current probe can be used to measure the
current flowing through the current loop.
Line Transient Response
Generate a step input voltage (V
of the output voltage, with an oscilloscope.
Load Transient Response
Generate a load current transient at the output, V
observe the output voltage response with an oscilloscope.
Use a current probe attached to the wire between the output
and the load to visualize the current transient.
Loop Stability Measurement
Closed-loop response can be measured using a network analyzer.
To measure the loop response, the IN and OUT headers are
available.
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Evaluation Board User Guide
I
OUT
I
IN
) and observe the behavior
IN
, and
OUT