QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 509 DUAL PHASE, SINGLE OUTPUT SYNCHRONOUS BUCK CONVERTER LTC3729EUH DESCRIPTION Demonstration circuit 509 is a single output step down The DC509A also contains a footprint for a 5.5V boost converter featuring the LTC3729EUH. The LTC3729EUH converter bias supply whose output is connected to is a dual phase controller with a frequency range of EXTVCC. See the Optional Bias Supply section below 250kHz to 550kHz in a 32 lead 5mm 5mm QFN pack- for more details. age. The QFN package has an exposed bottom pad that Design files for this circuit board are available. Call is soldered to the PCB and provides the LTC3729EUH the LTC factory. with low thermal impedance. The input voltage range of the DC509 is 5V to 14V and the output voltage is 2.5V with a load rating of 25A. Table 1. Performance Summary PARAMETER CONDITION VALUE Minimum Input Voltage 5V Maximum Input Voltage 14V V V = 5V to 14V, I = 0A to 25A 2.5V 3% OUT IN OUT QUICK START PROCEDURE Demonstration circuit 509 is easy to set up to evaluate 5. Keep the input voltage at 12.0V and the load at 25A. the performance of the LTC3729EUH. Refer to Figure 1 Measure the DC input current. It should be less than for proper measurement equipment setup and follow the 6.1A. procedure below: 6. Adjust the input voltage and load current to the de- 1. With power off, connect the input voltage source and sired levels within their limits and observe the regula- the load. The input cables should be sized to carry tion, output ripple, load step response, efficiency and current of at least 15A. The load cables need to be other parameters. sized for at least 30A. 7. If desired, the switching frequency of the converter 2. The jumpers should be placed in their default posi- may be adjusted with jumper JP1. The default posi- tions as shown in Figure 1. tion is 550kHz and the other position is 250kHz. 550kHz is a slight misnomer the actual PLLFLTR 3. If a constant current electronic load is used, preset signal will be 1.8V and this will result in a typical the load current to about 1A or less before applying switching frequency of roughly 500kHz. A typical power to the input. Otherwise, the foldback current switching frequency of 550kHz can be achieved by limit function of the LTC3729 will be triggered during decreasing the value of R3 while in the 550kHz posi- startup and the converter will remain in current limit tion. By placing the jumper in the 250kHz position, during steady-state operation. the PLLFLTR signal will be tied to ground. The typical 4. Apply power to the input and set the input voltage to switching frequency will then be 250kHz. 12V. The output voltage should be 2.5V 3%. In- 8. The phasing between controller 1 and CLKOUT and crease the load to 25A. The output voltage should between controller 1 and 2 can be set with jumper still be within regulation. JP2. The default position is 90, which will result in a 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 509 DUAL PHASE, SINGLE OUTPUT SYNCHRONOUS BUCK CONVERTER 90 phase shift between the CLKOUT signal and con- possible and measure the output ripple directly across troller 1 and 180 phase shift between controllers 1 output capacitor C20 or C21. See Figure 2. and 2. Refer to the LTC3729 data sheet for more de- NOTE: For input voltages from 5V to 7V, connect the tails. input voltage to EXTVCC. Otherwise, the INTVCC volt- NOTE: When measuring the output voltage ripple, care age will fall out of regulation and the operation of the must be taken to avoid a long ground lead on the os- circuit may be affected. cilloscope probe. Make the connections as short as + + + LOAD Figure 1. Proper Setup for Measurement Equipment Figure 2. Measuring Output Ripple 2 + + +