QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1072B 1A MONOLITHIC SYNCHRONOUS BUCK REGULATOR LTC3561A DESCRIPTION Demonstration circuit 1072B is a step-down converter, using the LTC3561A monolithic synchronous buck regulator. The DC1072B has an input voltage range of 2.5V to 5.5V, and is capable of delivering up to 1A of output current. The output voltage of the DC1072B can be set as low as 0.8V, the reference voltage of the LTC3561A, and can go as high as 5V. At light load currents, the DC1072B operates in pulse-skipping mode - ideal for noise sensitive applications. Of course, in large load current applications, the DC1072B operates in continuous mode, providing high efficiency - over 95%. The DC1072B consumes less than 60 uA of quiescent current during sleep operation, and during shutdown, it consumes less than 1 uA. The DC1072B has a standard operating frequency of 1 MHz, but can be adjusted to frequencies as high as 4 MHz. Because of the high switching frequency of the DC1072B, small, low profile surface mount components are used in the circuit. These features, plus the LTC3561A coming in a small 8-Lead DFN package, make the DC1072B a perfect match for battery-powered, hand-held applications. Design files for this circuit board are available. Call the LTC factory. TM - Burst Mode is a trademark of Linear Technology Corporation Table 1. Performance Summary (TA = 25°C) PARAMETER CONDITIONS VALUE Minimum Input Voltage 2.5V Maximum Input Voltage 5.5V 1.2V ±4% (1.152V to 1.248V) Output Voltage VOUT Regulation VIN = 2.5V to 5.5V, IOUT = 0A to 1A 1.5V ±4% (1.44V to 1.56V) 1.8V ±4% (1.728V to 1.872V) Typical Output Ripple VOUT VIN = 5V, IOUT = 1A (20 MHz BW) <20mVP–P Operation Mode Pulse-Skipping - VIN = 3.3V, VOUT = 1.8V <100mA ±0.1A% Nominal Switching Frequency 1 MHz QUICK START PROCEDURE Demonstration Circuit 1072B is easy to set up to evaluate the performance of the LTC3561A. For proper measurement equipment configuration, set up the circuit according to the diagram in Figure 1. Before proceeding to test, insert shunts into JP1 OFF position, which connects the RUN pin to ground (GND), and thus, shuts down the circuit, and the 1.2V position of JP2. NOTE: When measuring the input or output voltage ripple, care must be taken to avoid a long 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1072B 1A MONOLITHIC SYNCHRONOUS BUCK REGULATOR 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. 2. 3. With the DC1072B set up according to the proper measurement and equipment 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. If desired, one can measure the shutdown supply current at this point. The supply current will be approximately 10 uA, or less, in shutdown. Turn on the circuit by inserting the shunt in header JP1 into the ON position. The output voltage should be regulating. Measure Vout it should measure 1.2V +/- 2% (1.176V to 1.224V). Vary the input voltage from 2.5V to 5.5V and adjust the load current from 0 to 1A. Vout should read between 1.2V +/- 4% (1.152V to 1.248V). 4. Measure the output ripple voltage at any output current level; it usually will measure less than 20 mVAC. 5. 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 0.87 us), and that the switch node waveform is rectangular in shape. Insert jumper JP1 shunt into the OFF position and move the 1.2V Vout shunt into any of the remaining output voltage options: 1.5V or 1.8V. Just as in the 1.2Vout 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). When finished, turn off the circuit (connecting the RUN pin to ground) by inserting the shunt in header JP1 into the OFF (upper) position. Connection Diagram 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1072B 1A MONOLITHIC SYNCHRONOUS BUCK REGULATOR Figure 1. Proper Measurement Equipment Setup Figure 2. Measuring Input or Output Ripple 3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1072B 1A MONOLITHIC SYNCHRONOUS BUCK REGULATOR Figure 3. Switching Operation VIN = 3.3V, VOUT = 1.5V, 1A Output Current Trace 1: Switch Voltage (2V/div) Trace 3: Output Voltage (20mV/div AC) 4 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1072B 1A MONOLITHIC SYNCHRONOUS BUCK REGULATOR Figure 4. Load Step Response VIN = 3.3V, VOUT = 1.5V, 900mA Load Step (0.1A <-> 1A) Trace 3: Output Voltage (100mV/div AC) Trace 4: Output Current (500 mA/div) 5 GND E2 2.65V-5.5V Cin3 22uF 16V + * Cin2 1uF OPT Cin1 10uF 6.3V Rs1 1M 0 2 SD/RT SVIN 1 JP1 Rset 549K, 1% 1 6 OFF ON 3 Cbyp OPT Rfilt PVIN SG ND 2 Rc 8 7 Cc 16.2K ITH VFB SW 3 1000pF PG ND 4 5 JP2 C1 OPT 8 7 SELECT USER Rfb5 OPT 1 2 VIN 1.8V Rfb4 200K, 1% 6.3V 2.2uH D1 Cout1 OPT 22uF L1 6 5 E1 4 3 VIN 1.5V Rfb3 287K, 1% Cffw 10pF 2 1 U1 LTC3561AEDD 1.2V Rfb2 499K, 1% Rfb1 249K, 1% Cout2 0.1uF + VOUT E5 GND E4 GND 1.8V/1.5V/1.2V Cout3 1.0A OPT E3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1072B 1A MONOLITHIC SYNCHRONOUS BUCK REGULATOR 6