QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1105 LOW VIN SYNCHRONOUS STEP-DOWN CONVERTER WITH TRACKING LTC3822EDD-1 DESCRIPTION Demonstration circuit 1105A is a high efficiency synchronous step-down DC/DC converter with output tracking featuring the LTC3822EDD-1 controller. The demo board is capable of providing 1.8V/8A from 2.75V to 4.5V input. 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 current sense threshold can easily be selected with the IPRG pin. Switching frequency is internally set at 550KHz. The frequency can be adjusted using PLLLPF pin. Tying PLLLPF pin to GND selects 300KHz operation; tying PLLLPF pin to VIN selects 750KHz operation. The switching frequency can also be externally synchronized from 250KHz to 750KHz using SYNC terminal (JP1 should be selected for Sync). The demo board has a tracking feature, allowing Vout to track an external voltage signal at TRACK terminal (JP2 selected for Track). Design files for this circuit board are available. Call the LTC factory. , LTC and LT are registered trademarks of Linear Technology Corporation. Table 1. Performance Summary (TA = 25°C) PARAMETER CONDITION VALUE Input Voltage Range 2.75V to 4.5V VOUT VIN = 2.75-4.5V, IOUT = 0A to 8A 1.8V ±2% Maximum load current IOUT VIN = 2.75-4.5V, VOUT = 1.8V 8A Typical Output Ripple Voltage VIN = 3.3V, IOUT = 4A, Fs = 550KHz (20MHz BW) 12mVP–P Typical Switching Frequency PLLLPF Pin Floating 550kHz QUICK START PROCEDURE Demonstration circuit 1105A is easy to set up to evaluate the performance of the LTC3822-1. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: (Initial jumper positions: JP1: PS; JP2: Soft Start) NOTE: When 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-4.5V) and GND (input return). 2. Connect the 1.8V load between Vout and GND (Initial load: 0 A). 3. Connect 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. Once the proper output voltage is established, adjust the load within the operating range and observe the 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1105 LOW VIN SYNCHRONOUS STEP-DOWN CONVERTER WITH TRACKING output voltage regulation, ripple voltage and other parameters. Figure 1. Proper Measurement Equipment Setup GND VIN Figure 2. Measuring Input or Output Ripple 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1105 LOW VIN SYNCHRONOUS STEP-DOWN CONVERTER WITH TRACKING 100 10000 Vo=1.8V Efficiency 90 E ffic ie nc y (% ) 70 100 Loss 60 50 10 40 30 PO W E R LO S S (mW ) 1000 80 1 20 Vin=3.3V 0.1 10 10 100 1k 10k LOA D CURRENT (mA ) Figure 3. Efficiency and Power Loss vs Load Current (Pulse Skipping, 550KHz) 3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1105 LOW VIN SYNCHRONOUS STEP-DOWN CONVERTER WITH TRACKING 4