Analog Devices ADP1872-EVALZ, Руководство пользователя

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ADP1872-EVALZ/ADP1873-EVALZ User Guide UG-057
Rev. A | Page 5 of 20
4. Ensure that the current direction is toward the output voltage
(TP_VOUT1) and that the clamp of the current probe is in the
closed, or locked, position.
5. Set the vertical scale to one-third of the total load current that
the converter is designed to deliver.
6. Set the timescale similar to how the switching and output
ripple waveforms were set.
7. Observe the inductor current waveform.
Obtaining Efficiency Measurements
To obtain more accurate efficiency measurements,
1.
Power down the device.
2. Remove the 3 inch wire loop between the source of Q1 and
the inductor terminal.
3. Power up the device.
4. Record the current and voltage readings.
Efficiency is calculated based on the measurements made between
the output and the input of the converter:
IN IN
OUT OUT
I V
I V
η
×
×
=
where:
V
OUT
is the dc voltage readout by the voltmeter that is connected to
the SMB terminal of the evaluation board or by the voltmeter
that is connected across the output capacitor that is located
farthest from the inductor terminal.
I
OUT
is the digital readout produced by the electronic load
equipment.
V
IN
is the dc voltage readout by the voltmeter.
I
IN
is the current readout from the current meter in series
between the high input voltage supply equipment and the
TP_VIN1 terminal of the evaluation board.
Assessing Line Regulation
To assess the line regulation,
1.
Vary the high input voltage.
2. Record the resultant changes on the dc level of the output
voltage (V
OUT
).
Examining Load Regulation
To examine the load regulation,
1.
Vary the load current through electronic load adjustments.
2. Record the resultant changes on the dc level of the output
voltage (V
OUT
).
Observing Transient Response
To observe the transient response,
1.
Power up the system (see the Powering Up and Powering
Down the Evaluation Board section).
2. Solder a 3 inch wire loop (from 10 gauge to 14 gauge)
between the source of Q1 and the inductor terminal.
3. Record instances where the output transient is out of phase
with the load. Such occurrences are caused by sudden changes
in the output load current and can be recorded by capturing
the inductor ripple current waveform and the output voltage
ac transient using the single acquisition feature of the
oscilloscope.
Evaluating Short-Circuit Protection
To evaluate the self-protection scheme of the ADP1873 during
output short-circuit events,
1.
Achieve steady state regulation.
2. Short the voltage output (TP_VOUT1) to TP_PGND.
The system then enters hiccup mode and remains in this mode
until the violation disappears (see the
ADP1872 / ADP1873 data
sheet for more details).
MODIFYING THE EVALUATION BOARD
For any given ADP1872 / ADP1873 evaluation board, an ADP1872
or ADP1873 IC can be used interchangeably as long as the pre-
trimmed frequency setpoint is the same for both ICs.
To maintain system stability throughout the entire load current
range, one component (passive or active) cannot be modified
without modifying the rest. Refer to the
ADP1872 / ADP1873
data sheet for information about how each of the following
elements can be adjusted, keeping in mind that any change
affects the entire system:
•
Feedback resistor divider
•
Inductor
•
Output capacitor
•
Compensation network
•
Output filter impedance (Z
FILT
)
•
Error amplifier output impedance (Z
COMP
)
•
Error amplifier gain (G
M
)
•
Current-sense loop gain (G
CS
)
•
Programmable current-sense gain (A
CS
)
•
Valley current limit setting
•
Crossover frequency