QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 438
TRIPLE PHASE, SINGLE OUTPUT STEP-DOWN CONVERTER
LTC3731CG
DESCRIPTION
Demonstration circuit 438 is a triple phase single
output synchronous buck converter featuring the
LTC
®
3731CG. This circuit can be used for desktop
computers and servers, notebook computers and
other high output current DC/DC converters. The
output voltage can be configured for either 2.5V or
1.8V and the maximum load current is 60A. The
input voltage range of DC438 is 9V to 14V.
The LTC3731CG requires a separate supply for its
internal control circuits and for its gate drivers.
DC438 is populated with a 5V LT1761 linear
regulator for this purpose. To obtain a higher
Table 1.
Performance Summary
PARAMETER
Minimum Input Voltage
Maximum Input Voltage
V
OUT
Airflow
V
IN
= 9V to 14V, I
OUT
= 0A to 60A
100% load
CONDITION
VALUE
9V
14V
2.5V ± 3%
1.8V ± 3%
≥100
LFM
bias/gate drive supply voltage, the user can apply
an external DC source to the “+5V” terminal on
DC438. The maximum voltage for this input is 7.0V.
DC438 also features an on-board high di/dt
dynamic load circuit to measure the load step
response. Refer to the “Dynamic Load Testing”
section for operating instructions.
Design files for this circuit board are available.
Call the LTC factory.
LTC is a trademark of Linear Technology Corporation
QUICK START PROCEDURE
Demonstration circuit 438 is easy to set up to
evaluate the performance of the LTC3731CG. Refer to
Figure 1 for proper measurement equipment setup
and follow the procedure below:
1. With power off, connect the input voltage source
and the load. The input cables should be sized for
20A and the load cables should be sized for 60A.
2. If an external bias supply is connected to “+5V”,
then the “5V SELECT” jumper should be in the
“EXT” position. The external bias supply should
be able to supply at least 100mA.
3. The jumpers should be in their default positions
as shown in Figure 1.
4. If a constant current load is used, preset the load
current to about 5A or less before applying power
to the input. Otherwise, the foldback current limit
function of the LTC3731 will be triggered during
startup.
5. Apply power to the input and set the input voltage
to 12V. The output voltage should be 2.5V ± 3%.
Increase the load to 60A. The output voltage
should still be within regulation.
6. Keep the input voltage at 12.0V and the load at
60A. Measure the DC input current. It should be
less than 15.2A.
7. Remove input power from the converter. Set the
voltage to 1.8V using jumper JP3. Apply 12V to
the input and 60A to the output. The voltage
should be 1.8V ± 3%.
8. For operation at 100% load and room tempera-
ture ambient, use 100 LFM airflow or greater.
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 438
TRIPLE PHASE, SINGLE OUTPUT STEP-DOWN CONVERTER
9. Adjust the input voltage and load current to the
desired levels within their limits and observe the
regulation, output ripple, load step response,
efficiency and other parameters.
NOTE:
The BNC connectors labeled “VOUT+” and
“LOAD STEP” can be used to monitor the output
voltage and load step waveforms, respectively, on an
oscilloscope.
DYNAMIC LOAD TESTING
DC438 is populated with a high di/dt dynamic load
circuit that is capable of applying a 0A to 60A load
step to the output. The lower level of the step is
fixed at 0A. To test this circuit, follow the
instructions below:
1) Put both the “DLC” jumper and the “DLC BIAS”
jumper in the “ON” position.
2) Turn-on the converter and set the external load
to the low level of the load step.
3) Adjust potentiometers R38, R34 and R33 to set
the height, up slope and down slope of the load
step respectively.
4) Monitor the load step current and output volt-
age. For the load step current, 5mV = 1A.
Figure 1. Proper Measurement Equipment Setup
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