Analog Devices UG-189 User Manual page 4

UG-189
Measuring Output Voltage Ripple
To observe the output voltage ripple, place an oscilloscope probe
across the output capacitor (C3) with the probe ground lead
placed at the negative (−) capacitor terminal and the probe tip
placed at the positive (+) capacitor terminal. Set the oscilloscope to
ac, 10 mV/division, 2 μs/division time base, and 20 MHz
bandwidth.
A standard oscilloscope probe has a long wire ground clip. For
high frequency measurements, this ground clip picks up high
frequency noise and injects it into the measured output ripple.
Figure 2 shows an easy way to measure the output ripple properly.
It requires removing the oscilloscope probe sheath and wrapping a
nonshielded wire around the oscilloscope probe. By keeping the
ground length of the oscilloscope probe as short as possible,
true ripple can be measured.
Output Voltage Change
The ADP2302/ADP2303
however, the output voltage can be adjusted using the following
equation:
=
V 0.8
OUT
Figure 2. Measuring Output Voltage Ripple
Rev. 0 | Page 4 of 12
Evaluation Board User Guide
evaluation board output is preset to 3.3 V;
R5 + R3
⎛ ⎞
×
V
⎜ ⎟
⎝ R5 ⎠