QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1159A 4MHZ, 1.25A MONOLITHIC SYNCHRONOUS BUCK REGULATOR LTC3565 DESCRIPTION Demonstration circuit 1159A is a high efficiency LTC3565 ideally suited for single Li-Ion battery- monolithic synchronous buck regulator using a powered or 3.3V to 5V input voltage applications. constant frequency, current mode LTC3565. Its 100% duty cycle provides low dropout operation, high switching frequency of 2.25MHz allows the extending battery life in portable systems. Auto- use of small surface mount inductors and capaci- matic Burst Mode operation increases efficiency tors. Supply current during operation is typically at light loads, further extending battery runtime. only 20uA, and drops to below 1uA in shutdown. Gerber files for this circuit are available. Call The 2.5V to 5.5V input voltage range makes the the LTC Factory. Table 1. Performance Summary (T = 25C) A PARAMETER CONDITION VALUE Input Voltage 2.5V to 5.5V Output Voltage I =0A to 1.25A V 1% OUT OUT Maximum Output Current 1.25A DC Supply Current V = 3.3V, V = 1.8V, I = 0A <100A IN OUT OUT Nominal Switching Frequency V = 3.3V, V = 1.8V, I = 1.25A 2.25MHz IN OUT OUT QUICK START PROCEDURE The DC1159A is easy to set up to evaluate the 2. Before proceeding to operation, insert performance of the LTC3565. Refer to Figure 2 jumper shunt XJP1 into the pulse-skip mode, for the proper measurement equipment setup. jumper shunt XJP2 into the OFF position and insert one jumper shunt into XJP3, XJP4, or NOTE: When measuring the input or output volt- XJP5 for an output voltage of 1.8V, 1.5V, or age ripple, care must be taken to avoid a long 1.2V respectively. Set the load output current to ground lead on the oscilloscope probe. Measure less than 1.25A. An optional output voltage can the input or output voltage ripple by touching the be set by populating resistor RFB5 and moving probe tip directly across the V or V and GND IN OUT the shunt to header JP5. terminals. See the measurement example dia- gram in Figure 1 for proper scope probe measur- 3. Apply 5V at V . Measure V it should IN OUT ing technique. read 0V. If desired, one can measure the shut- down supply current at this point. The supply cur- Please follow the procedure outlined below for rent will be less than 10 A in shutdown. proper operation. 4. Turn on V by changing shunt XJP2 from OUT 1. Connect the input power supply to the V IN the OFF position to the ON position. The out- and GND terminals. Connect the load between put voltage should measure according to the the V and GND terminals. OUT 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1159A 4MHZ, 1.25A MONOLITHIC SYNCHRONOUS BUCK REGULATOR voltage set by the shunt in headers JP2, JP3, or 6. Vary the V load current from 0 to 1.25A, OUT JP4. and the output voltage should be within a toler- ance of +/- 1%. 5. Vary the input voltage between 2.5V and 5.5V and the output voltage should be within +/- 7. Observe the switch node, pin 4. The wave- 1% tolerance. form should be a rectangular, pulse-width modulated one, with a frequency of approx. 2.25 MHz. Warning - If the power for the demo board is between the input power and return terminals on supplied with long leads, the input voltage at the the bottom of the demo board. The ESR of the part could ring, which could affect the operation tantalum will dampen the (possible) ringing volt- of the circuit or even exceed the maximum volt- age due to the use of long input leads. On a age rating of the IC. To eliminate the ringing, normal, typical PCB, with short traces, the ca- insert a small tantalum capacitor on the pads pacitor is not needed. Figure 1. Measuring Input or Output Ripple Figure 2. Proper Measurement Equipment Setup 2