QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1206 1.8A, 4 MHZ SYNCHRONOUS STEP-DOWN DC/DC CONVERTER LTC3568 DESCRIPTION Demonstration circuit 1206 is a step-down converter, using the LTC3568 monolithic synchronous buck regulator. The DC1206 has an input voltage range of 2.25V to 5.5V, and is capable of delivering up to 1.8A of output current at a minimum input voltage of 2.25V. The output voltage of the DC1206 can be set as low as 0.8V, the reference voltage of the LTC3568. At low load currents, the DC1206 can operate in either noise sensitive applications, due to the capability of the LTC3568 to operate in pulseskipping mode, or in high efficiency applications, because the LTC3568 can also operate in BurstMode®. During Burst-Mode® operation, the output ripple voltage is still low – less than 30 mV – due to the improvements made in the design of the LTC3568. Of course, in continuous mode, or large load current applications, the DC1206 is a high efficiency circuit - over 95%. The DC1206 consumes less than 70 uA of quiescent current during sleep operation typically, and during shutdown, it consumes less than 1 uA. Because of the high switching frequency of the LTC3568, which is programmable up to 4 MHz, the DC1206 uses low profile surface mount components. These features, plus the LTC3568 coming in a small 10-Lead DFN package, make the DC1206 an ideal circuit for use in battery-powered, hand-held applications. Design files for this circuit are available. Call the LTC Factory. LTC is a trademark of Linear Technology Corporation Table 1. Performance Summary (TA = 25°C) PARAMETER CONDITIONS VALUE Minimum Input Voltage 2.25V Maximum Input Voltage 5.5V GND = Shutdown Run/Shutdown VIN = Run 1.2V ±4% (1.152V – 1.248V) Output Voltage VOUT VIN = 2.25V to 5.5V, IOUT = 0A to 1.8A 1.5V ±4% (1.44V - 1.56V) 1.8V ±4% (1.728V – 1.872V) Typical Output Ripple VOUT Operation Modes Nominal Switching Frequency VIN = 3.3V, VOUT = 1.8V, IOUT = 1.8A (20 MHz BW) < 20mVP–P Burst Mode - VIN = 3.3V, VOUT = 1.8V < 500 mA Pulse-Skip - VIN = 3.3V, VOUT = 1.8V < 425 mA RT = 324k 1 MHz 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1206 1.8A, 4 MHZ SYNCHRONOUS STEP-DOWN DC/DC CONVERTER QUICK START PROCEDURE Demonstration Circuit 1206 is easy to set up to evaluate the performance of the LTC3568. For proper measurement equipment configuration, set up the circuit according to the diagram in Figure 1. Before proceeding to test, insert shunts into the OFF position of header JP3, which connects the RUN pin to ground (GND), and thus, shuts down the circuit, the pulseskip position of header JP1, and the 1.8V output voltage header – JP2. 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 measurement technique. With the DC1206 set up according to the proper measurement and equipment set-up in Figure 1, apply 3.3V at Vin (Do not hot-plug Vin or increase Vin over the rated maximum supply voltage of 5.5V, or the part may be damaged.). Measure Vout; it should read 0V. Turn on the circuit by inserting the shunt in header JP3 into the ON position. The output voltage should be regulating. Measure Vout - it should measure 1.8V +/- 2% (1.764V to 1.836V). Vary the input voltage from 2.25V to 5.5V and adjust the load current from 0 to 1.8A. Vout should read 1.8V +/- 4% (1.728V to 1.872V). Adjust the output current to 1A. Measure the output ripple voltage; it will measure less than 20 mVAC. Observe the voltage waveform at the switch node. Verify the switching frequency is between 850 kHz and 1.15 MHz (T = 1.176 us and 0.869 us), and that the switch node waveform is rectangular in shape. Adjust the input voltage to 3.3V and the output current to any current less than 400 mA. Observe the pulse-skip mode of operation at the switch node. Also, measure the output ripple voltage; it should measure less than 20 mV. Change the JP1 shunt from pulse-skip mode to Burst Mode®. Observe the Burst Mode® operation at the switch node, and measure the output ripple voltage. It should measure less than 50 mV. Insert the JP3 shunt into the OFF position and move the 1.8V Vout JP2 shunt into any of the two remaining output voltage option headers: 1.2V or 1.5V. Just as in the 1.8Vout test, the output voltage should read Vout +/- 2% tolerance under static line and load conditions, and +/- 1% tolerance under dynamic line and load conditions (+/- 2% total). Also, circuit operation in either Burst Mode® or pulse-skip mode will be the same. When finished, turn off the circuit by inserting the shunt in header JP3 into the OFF position (connecting the RUN pin to ground). 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1206 1.8A, 4 MHZ SYNCHRONOUS STEP-DOWN DC/DC CONVERTER Figure 1. Proper Equipment Measurement Set-Up Figure 2. Measuring Input or Output Ripple 3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1206 1.8A, 4 MHZ SYNCHRONOUS STEP-DOWN DC/DC CONVERTER Normal Switching Frequency & Output Ripple Voltage Waveforms Figure 3. Switch Waveform & Output Ripple Voltage V = 3.3V, V = 1.8V, I = 1.8A IN OUT OUT Trace 2: Switch Voltage (2 V/div) Trace 3: Output Ripple Voltage (20 mV/div AC) 4 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1206 1.8A, 4 MHZ SYNCHRONOUS STEP-DOWN DC/DC CONVERTER Load Step Response Waveform Figure 4. Load Step Response V = 3.3V, V = 1.8V, 1.62A Load Step (180mA <-> 1.8A) IN OUT Pulse-Skip Mode Fsw = 1 MHz Trace 3: Output Voltage (50mV/div AC) Trace 4: Output Current (1A/div) 5 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1206 1.8A, 4 MHZ SYNCHRONOUS STEP-DOWN DC/DC CONVERTER 6