QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 542
DUAL PHASE, DUAL OUTPUT SYNCHRONOUS BUCK CONVERTER
1
LTC3728EG
DESCRIPTION
Demonstration circuit 542 is a dual output, dual
phase step down converter, which is controlled
by the LTC3728EG. Output #1 can be configured
for either 5.0V or 3.3V and output #2 can be
configured for either 3.3V or 2.5V. The maximum
load for both rails is 12A. The input voltage
range of the DC542 is 8V to 24V.
The DC542 also contains a footprint for a 5.5V
boost converter bias supply whose output is
connected to EXTVCC. See the “Optional Bias
Supply” section for more details.
Design files for this circuit board are avail-
able. Call the LTC factory.
Table 1. Performance Summary
PARAMETER CONDITION
VALUE
Minimum Input Voltage
8V
Maximum Input Voltage
24V
V
OUT1
V
IN
= 8V to 24V, I
OUT
= 0A to 12A
5.0V ± 3% / 3.3V ± 3%
V
OUT2
V
IN
= 8V to 24V, I
OUT
= 0A to 12A
3.3V ± 3% / 2.5V ± 3%
QUICK START PROCEDURE
Demonstration circuit 542 is easy to set up. Re-
fer to Figure 1 for the proper setup of the meas-
urement equipment and follow the procedure
below:
1. With power off, connect the input voltage
source and the load. The load cables should
be sized for 12 Amps and the input cables
should be sized for 15 Amps.
2. The jumpers should be placed in their default
positions as shown in Figure 1.
3. If a constant current electronic load is used,
preset the load current to about 1A or less
before applying power to the input. Other-
wise, the foldback current limit function of the
LTC3728 may be triggered during startup.
4. Apply power to the input and set the input
voltage to 12V. The voltage for output #1
should be 5.0V ± 3% and the voltage for out-
put #2 should be 3.3V ± 3%. Increase the
load on both rails to 12.0A. The two outputs
should still be within regulation.
5. Keep the input voltage at 12.0V and the load
at 12.0A for both rails. Measure the DC input
current. It should be less than 9.4A.
6. Remove input power from the converter. Set
the voltage for output #1 to 3.3V using
jumper JP5 and the voltage for output #2 to
2.5V using JP4. Repeat step #4. The voltage
for output #1 should be 3.3V ± 3% and the
voltage for output #2 should be 2.5V ± 3%.
7. Adjust the input voltage and load current to
the desired levels within their limits and ob-
serve the regulation, output ripple, load step
response, efficiency and other parameters.
