QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 542 DUAL PHASE, DUAL OUTPUT SYNCHRONOUS BUCK CONVERTER LTC3728EG DESCRIPTION Demonstration circuit 542 is a dual output, dual The DC542 also contains a footprint for a 5.5V phase step down converter, which is controlled boost converter bias supply whose output is by the LTC3728EG. Output 1 can be configured connected to EXTVCC. See the Optional Bias for either 5.0V or 3.3V and output 2 can be Supply section for more details. configured for either 3.3V or 2.5V. The maximum Design files for this circuit board are avail- load for both rails is 12A. The input voltage able. Call the LTC factory. range of the DC542 is 8V to 24V. Table 1. Performance Summary PARAMETER CONDITION VALUE Minimum Input Voltage 8V Maximum Input Voltage 24V V V = 8V to 24V, I = 0A to 12A 5.0V 3% / 3.3V 3% OUT1 IN OUT V V = 8V to 24V, I = 0A to 12A 3.3V 3% / 2.5V 3% OUT2 IN OUT QUICK START PROCEDURE Demonstration circuit 542 is easy to set up. Re- put 2 should be 3.3V 3%. Increase the fer to Figure 1 for the proper setup of the meas- load on both rails to 12.0A. The two outputs urement equipment and follow the procedure should still be within regulation. below: 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. 1. With power off, connect the input voltage source and the load. The load cables should 6. Remove input power from the converter. Set be sized for 12 Amps and the input cables the voltage for output 1 to 3.3V using should be sized for 15 Amps. jumper JP5 and the voltage for output 2 to 2.5V using JP4. Repeat step 4. The voltage 2. The jumpers should be placed in their default for output 1 should be 3.3V 3% and the positions as shown in Figure 1. voltage for output 2 should be 2.5V 3%. 3. If a constant current electronic load is used, 7. Adjust the input voltage and load current to preset the load current to about 1A or less the desired levels within their limits and ob- before applying power to the input. Other- serve the regulation, output ripple, load step wise, the foldback current limit function of the response, efficiency and other parameters. 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- 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 542 DUAL PHASE, DUAL OUTPUT SYNCHRONOUS BUCK CONVERTER Figure 1. Setup for measurement equipment. Figure 2. Output ripple measurement. Note: When measuring the output voltage ripple, care must be taken to avoid a long ground lead on the oscilloscope probe. Connect the probe tip to VOUT and the probes ground ring to GND. Make the connections as short as possible. For output 1, measure the ripple directly across C35 and for output 2, measure across C36. See Figure 2. 2