Evaluation Board User Guide UG-249
Rev. 0 | Page 3 of 8
USING THE EVALUATION BOARD
POWERING UP THE EVALUATION BOARD
The ADP2138/ADP2139 evaluation board is supplied fully
assembled and tested. Before applying power to the evaluation
board, follow the procedures in this section.
Jumper TB2 (Enable)
Jumper TB2 (EN) enables/disables the ADP2138/ADP213.
Connect a jumper between TB2 and TB1 (VIN) to enable the
ADP2138/ADP2139. Connecting TB2 (EN) to TB4 (GND)
disables the ADP2138/ADP2139 and brings the current to
< 1 μA.
Input Power Source
If the input power source includes a current meter, use that meter
to monitor the input current. Connect the positive terminal of
the power source to TB1 (V
IN
) on the evaluation board, and the
negative terminal of the power source to TB4 (GND OUT) of the
evaluation board.
If the power source does not include a current meter, connect a
current meter in series with the input source voltage. Connect the
positive lead (+) of the power source to the ammeter positive (+)
connection, the negative lead (−) of the power source to TB4 (GND
OUT) on the evaluation board, and the negative lead (−) of the
ammeter to TB1 (V
IN
) on the board.
Output Load
Connect an electronic load or resistor to set the load current. If the
load includes an ammeter, or if the current is not measured, con-
nect the load directly to the evaluation board, with the positive (+)
load connection to TB3 (V
OUT
) and the negative (−) load
connection to TB4 (GND).
If an ammeter is used, connect it in series with the load. Connect
the positive (+) ammeter terminal to the evaluation board TB3
(VOUT), the negative (−) ammeter terminal to the positive (+)
load terminal, and the negative (−) load terminal to the evaluation
board TB4 (GND OUT).
Input and Output Voltmeters
Measure the input and output voltages with voltmeters. Make
sure that the voltmeters are connected to the appropriate eval-
uation board terminals and not to the load or power source
themselves. If the voltmeters are not connected directly to the
evaluation board, the measured voltages are incorrect due to
the voltage drop across the leads and/or connections between
the evaluation board, the power source, and/or the load.
Connect the input voltage measuring voltmeter positive termi-
nal (+) to the evaluation board TB1 (VIN), and the negative (−)
terminal to the evaluation board TB4 (GND OUT). Connect the
output voltage measuring voltmeter positive (+) terminal to the
evaluation board TB3 (VOUT) and the negative (−) terminal to
the evaluation board TB4 (GND OUT).
Turning On the Evaluation Board
Once the power source and load are connected to the
ADP2138/ADP2139 evaluation board, the board can be
powered for operation. Perform the following steps:
1. Ensure that the power source voltage is > 2.3 V and < 5.5 V.
2. Ensure that TB2 (EN) is high and monitor the output
voltage.
If the load is not already enabled, enable the load, check that it is
drawing the proper current, and that the output voltage maintains
voltage regulation.
Changing the Mode of the Device
Each ADP2138/ADP2139 has a MODE pin, which determines the
operation of the buck regulator in either PWM mode (when the
MODE pin is set high by connecting TB6 to TB1) or power save
mode (when the mode pin is set low by connecting TB6 to TB4).
MEASURING EVALUATION BOARD PERFORMANCE
Measuring Output Voltage Ripple
To observe the output voltage ripple, place an oscilloscope probe
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, 20 mV/division,
and 2 μs/division time base.
Measuring the Switching Waveform
To observe the switching waveform with an oscilloscope,
place the oscilloscope probe tip at the end of the inductor with
the probe ground at GND OUT. Set the oscilloscope to dc,
2 V/division, and 2 μs/division time base.
Measuring Load Regulation
The load regulation must be tested by increasing the load at the
output and looking at the change in output voltage. To mini-
mize voltage drop, use short low resistance wires, especially for
loads approaching maximum current.
Measuring Line Regulation
Vary the input voltage and examine the change in the output
voltage.
Measuring Efficiency
Measure the efficiency, η, by comparing the input power with
the output power.
ININ
OUTOUT
IV
IV
η
×
=
Measure the input and output voltages as close as possible to the
input and output capacitors to reduce the effect of IR drops.
Measuring Inductor Current
The inductor current can be measured by removing one end
of the inductor from its pad and connecting a current loop in
series. A current probe can be connected onto this wire.
