QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 803 2-PHASE DUAL SYNCHRONOUS STEP-DOWN CONVERTER WITH SPREAD SPECTRUM AND OUTPUT TRACKING LTC3736EUF-1 DESCRIPTION Demonstration circuit 803 is a high efficiency 2-phase dual synchronous step-down DC/DC converter with 2.75V to 8V input range. It has two outputs: 2.5V (5A maximum at 5V input) and 1.8V (5A maximum at 5V input). The demo circuit features the LTC(R)3736EUF-1 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. to GND selects 300kHz operation; tying FREQ pin to VIN selects 750kHz operation. The demo board can be selected to operate in spread spectrum mode (JP1: Enable) with significantly reduced peak switching noise. The board has tracking function too, allowing VOUT2 to track VOUT1 during startup. Switching frequency is internally set at 550kHz. The frequency can also be adjusted using FREQ pin (with spread spectrum operation disabled). Tying FREQ pin LTC is a trademark of Linear Technology Corporation Design files for this circuit board are available. Call the LTC factory. Table 1. Performance Summary (TA = 25C) PARAMETER CONDITION VALUE Input Voltage Range VOUT1 2.75V to 8V VIN = 2.75-8V, IOUT1 = 0A to 5A, 2.5V 3% IOUT2 = 0A to 5A VOUT2 VIN = 2.75-8V, IOUT1 = 0A to 5A, 1.8V 3% IOUT2 = 0A to 5A Typical Output Ripple VOUT1 VIN = 3.3V, IOUT1 = 3A (20MHz BW) 20mVP-P Typical Output Ripple VOUT2 VIN = 3.3V, IOUT2 = 3A (20MHz BW) 14mVP-P Typical Switching Frequency FREQ Pin Floating; Spread Spectrum: Disable 550kHz Typical Spread Spectrum Frequency Range Spread Spectrum: Enable 450kHz- 580kHz QUICK START PROCEDURE Demonstration circuit 803 is easy to set up to evaluate the performance of LTC3736-1. Refer to Figure 1. for proper measurement equipment setup and follow the procedure below: NOTE: When measuring the input or output voltage ripple, care must be taken to avoid a long ground lead on the oscilloscope probe. (it's recommended to measure the output ripple directly at the main output capacitor). 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 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 803 2-PHASE DUAL SYNCHRONOUS STEP-DOWN CONVERTER WITH SPREAD SPECTRUM AND OUTPUT TRACKING Figure 1) between Vout2 and GND. (Initial loads: 0A) 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+/3%. Vout2 should be 1.8V+/-3%. 5. Once the proper output voltages are established, adjust the loads within the operating range and observe the output voltage regulation, ripple voltage and other parameters. Figure 1. Proper Measurement Equipment Setup 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 803 2-PHASE DUAL SYNCHRONOUS STEP-DOWN CONVERTER WITH SPREAD SPECTRUM AND OUTPUT TRACKING 100 V o=2.5V EFFICIENCY (%) 90 V o=1.8V 80 70 60 50 V in=3.3V 40 1 10 100 1k 10k LO A D C U R R E N T (mA ) Figure 2. Efficiency vs load current (550kHz) 3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 803 2-PHASE DUAL SYNCHRONOUS STEP-DOWN CONVERTER WITH SPREAD SPECTRUM AND OUTPUT TRACKING 4