QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 882 SYNCHRONOUS STEP-DOWN CONVERTER WITH OUTPUT TRACKING LTC3809EDD-1 DESCRIPTION Demonstration circuit 882 is a small size, low profile, low cost and high efficiency synchronous step-down DC/DC converter featuring the LTC3809EDD-1 controller. The demo board is capable of providing 2A output current with 2.75V to 9.8V input range. Burst mode/Pulse skipping/Forced continuous operation is selectable. The constant frequency current mode architecture with MOSFET VDS sensing eliminates the need for a sense resistor and improves efficiency. The maximum peak cur- rent sense threshold can be easily selected with IPRG pin. Switching frequency is internally set at 550KHz. The demo board has optional power component footprints to deliver higher output current and a tracking function, allowing Vout to track an external voltage signal at the TRACK terminal (JP4: Track). Design files for this circuit board are available. Call the LTC factory. LTC is a trademark of Linear Technology Corporation Table 1. Performance Summary (TA = 25°C) PARAMETER CONDITION VALUE Input Voltage Range 2.75V to 9.8V VOUT VIN = 2.75V-9.8V, IOUT = 0A to 2A 1.8V ±2.5% Maximum load current IOUT VIN = 2.75V-9.8V 2A Typical Output Ripple Voltage VIN = 3.3V, IOUT = 2A (20MHz BW) 8mVP–P Typical Switching Frequency 550kHz QUICK START PROCEDURE Demonstration circuit 882 is easy to set up to evaluate the performance of the LTC3809-1. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: (Initial jumper positions: JP1 selected; JP4: Soft Start) 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. 2. Connect the 1.8V load between Vout and GND (Initial load: 0 A). 3. Connect the DVMs to the input and output. 4. Turn on the input power supply and check for the proper output voltage. Vout should be 1.8V+/-2.5%. 5. Once the proper output voltage is established, adjust the load within the operating range and observe the output voltage regulation, ripple voltage and other parameters. NOTE: When 1. With power off, connect the input power supply to Vin (2.75V-9.8V) and GND (input return). 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 882 SYNCHRONOUS STEP-DOWN CONVERTER WITH OUTPUT TRACKING Figure 1. Proper Measurement Equipment Setup GND VIN Figure 2. Measuring Input or Output Ripple 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 882 SYNCHRONOUS STEP-DOWN CONVERTER WITH OUTPUT TRACKING 10000 100 Vo=1.8V 1000 80 100 Loss 70 10 POWER LOSS (mW) EFFICIENCY (%) Efficiency 90 1 60 Vin=3.3V 0.1 50 1 10 100 1k 10k LOAD CURRENT (mA) Figure 3. Efficiency and Loss vs Load Current (Burst Mode) 3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 882 SYNCHRONOUS STEP-DOWN CONVERTER WITH OUTPUT TRACKING 4