DC438A - ANALOG DEVICES - Datasheet.Live

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

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

Table 1.

Performance Summary

PARAMETER CONDITION VALUE

Minimum Input Voltage 9V

Maximum Input Voltage 14V

VOUT V

IN = 9V to 14V, IOUT = 0A to 60A 2.5V ± 3%

1.8V ± 3%

Airflow 100% load ≥100 LFM

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.

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