QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1072B 1A MONOLITHIC SYNCHRONOUS BUCK REGULATOR LTC3561A DESCRIPTION Demonstration circuit 1072B is a step-down con- than 1 uA. The DC1072B has a standard operat- verter, using the LTC3561A monolithic synchro- ing frequency of 1 MHz, but can be adjusted to nous buck regulator. The DC1072B has an input frequencies as high as 4 MHz. Because of the voltage range of 2.5V to 5.5V, and is capable of high switching frequency of the DC1072B, small, delivering up to 1A of output current. The output low profile surface mount components are used in voltage of the DC1072B can be set as low as the circuit. These features, plus the LTC3561A 0.8V, the reference voltage of the LTC3561A, and coming in a small 8-Lead DFN package, make the can go as high as 5V. At light load currents, the DC1072B a perfect match for battery-powered, DC1072B operates in pulse-skipping mode - ideal hand-held applications. for noise sensitive applications. Of course, in large load current applications, the DC1072B op- Design files for this circuit board are avail- erates in continuous mode, providing high effi- able. Call the LTC factory. ciency - over 95%. The DC1072B consumes less than 60 uA of quiescent current during sleep op- TM - Burst Mode is a trademark of Linear Technology Corporation eration, and during shutdown, it consumes less Table 1. Performance Summary (T = 25C) A PARAMETER CONDITIONS VALUE Minimum Input Voltage 2.5V Maximum Input Voltage 5.5V 1.2V 4% (1.152V to 1.248V) Output Voltage V Regulation V = 2.5V to 5.5V, I = 0A to 1A 1.5V 4% (1.44V to 1.56V) OUT IN OUT 1.8V 4% (1.728V to 1.872V) Typical Output Ripple V V = 5V, I = 1A (20 MHz BW) <20mV OUT IN OUT PP Operation Mode Pulse-Skipping - V = 3.3V, V = 1.8V <100mA 0.1A% IN OUT Nominal Switching Frequency 1 MHz QUICK START PROCEDURE Demonstration Circuit 1072B is easy to set up shunts into JP1 OFF position, which connects to evaluate the performance of the LTC3561A. the RUN pin to ground (GND), and thus, shuts For proper measurement equipment configura- down the circuit, and the 1.2V position of JP2. tion, set up the circuit according to the diagram NOTE: When measuring the input or output volt- in Figure 1. Before proceeding to test, insert age 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. Meas- should read between 1.2V +/- 4% (1.152V to ure the input or output voltage ripple by touch- 1.248V). ing the probe tip directly across the Vin or Vout 4. Measure the output ripple voltage at any out- and GND terminals. See Figure 2 for proper put current level it usually will measure less scope probe technique. than 20 mVAC. 1. With the DC1072B set up according to the 5. Observe the voltage waveform at the switch proper measurement and equipment in Fig- node. Verify the switching frequency is be- ure 1, apply 3.3V at Vin (Do not hot-plug Vin tween 850 kHz and 1.15 MHz (T = 1.176 us or increase Vin over the rated maximum sup- and 0.87 us), and that the switch node wave- ply voltage of 5.5V, or the part may be dam- form is rectangular in shape. aged.). Measure Vout it should read 0V. If Insert jumper JP1 shunt into the OFF position and desired, one can measure the shutdown sup- move the 1.2V Vout shunt into any of the remain- ply current at this point. The supply current ing output voltage options: 1.5V or 1.8V. Just as will be approximately 10 uA, or less, in shut- in the 1.2Vout test, the output voltage should read down. Vout +/- 2% tolerance under static line and load 2. Turn on the circuit by inserting the shunt in conditions, and +/- 1% tolerance under dynamic header JP1 into the ON position. The output line and load conditions (+/- 2% total). voltage should be regulating. Measure Vout - When finished, turn off the circuit (connecting it should measure 1.2V +/- 2% (1.176V to the RUN pin to ground) by inserting the shunt in 1.224V). header JP1 into the OFF (upper) position. 3. Vary the input voltage from 2.5V to 5.5V and adjust the load current from 0 to 1A. Vout Connection Diagram 2