QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 922 2-PHASE DUAL SYNCHRONOUS STEP-DOWN CONVERTER WITH OUTPUT TRACKING LTC3736EUF-2 DESCRIPTION Demonstration circuit 922A is a 2-phase dual synchronous high efficiency step-down DC/DC converter with 2.75V to 8V input range. It has two outputs: 2.5V (6A MAX) and 1.8V (6A MAX). The demo circuit features the LTC®3736EUF-2 controller. The constant frequency current mode architecture with MOSFET VDS sensing eliminates the need for sense resistors and improves efficiency. Out of phase operation significantly reduces input ripple current as well as the input capacitor size. frequency can also be selected with the PLLLPF pin. Tying the PLLLPF pin to GND selects 300KHz operation; tying the PLLLPF pin to VIN selects 750KHz operation. The demo circuit has a tracking function, allowing VOUT2 to track VOUT1 during start-up. Design files for this circuit board are available. Call the LTC factory. Switching frequency is internally set at 550KHz. For noise sensitive applications, the converter can be externally synchronized from 250KHz to 850KHz. The , LTC and LT are registered trademarks of Linear Technology Corporation. Table 1. Performance Summary (TA = 25°C) PARAMETER CONDITION VALUE Input Voltage Range VOUT1 2.75V to 8V VIN = 2.75-8V, IOUT1 = 0A to 6A, 2.5V ±2.5% IOUT2 = 0A to 6A VOUT2 VIN = 2.75-8V, IOUT1 = 0A to 6A, 1.8V ±2.5% IOUT2 = 0A to 6A Typical Output Ripple VOUT1 VIN = 3.3V, IOUT1 = 3A (20MHz BW) 22mVP–P Typical Output Ripple VOUT2 VIN = 3.3V, IOUT2 = 3A (20MHz BW) 12mVP–P Typical Switching Frequency PLLLPF Pin Floating 550kHz QUICK START PROCEDURE Demonstration circuit 922A is easy to set up to evaluate the performance of the LTC3736EUF-2. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: measuring the input or output voltage ripple, care must be taken to avoid a long ground lead on the oscilloscope probe. Measure the input or output voltage ripple by touching the probe tip directly across the Vin or Vout and GND terminals. See Figure 2 for proper scope probe technique. 1. With power off, connect the input power supply to +Vin (2.75V-8V) and GND (input return). 2. Connect the 2.5V load (Load 1 in Figure 1) between Vout1 and GND; connect the 1.8V load (Load 2 in Figure 1) between Vout2 and GND. (Initial loads: no load.) 3. Connect the DVMs to the input and outputs. 4. Turn on the input power supply and check for the proper output voltages. Vout1 should be 2.5V+/2.5%. Vout2 should be 1.8V+/-2.5%. NOTE: When 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 922 2-PHASE DUAL SYNCHRONOUS STEP-DOWN CONVERTER WITH OUTPUT TRACKING 5. Once the proper output voltages are established, adjust the loads within the operating range and ob- serve the output voltage regulation, ripple voltage and other parameters. Figure 1. Proper Measurement Equipment Setup Figure 2. Measuring Input or Output Ripple 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 922 2-PHASE DUAL SYNCHRONOUS STEP-DOWN CONVERTER WITH OUTPUT TRACKING 2.5Vout Efficiency 3.3Vin, Cont 95.0% 90.0% 5Vin, Cont Efficiency (%) 85.0% 80.0% 75.0% 3.3Vin, Pulse Skip 70.0% 65.0% 5Vin, Pulse Skip 60.0% 55.0% 50.0% 0 2 4 6 8 10 Load Current (A) Efficiency (%) 1.8Vout Efficiency 3.3Vin, Cont 95.0% 90.0% 85.0% 80.0% 75.0% 70.0% 65.0% 60.0% 55.0% 50.0% 5Vin, Cont 3.3Vin, Pulse Skip 5Vin, Pulse Skip 0 2 4 6 8 10 Load Current (A) Figure 3. Efficiency vs load current (550KHz) 3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 922 2-PHASE DUAL SYNCHRONOUS STEP-DOWN CONVERTER WITH OUTPUT TRACKING 4