QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1343A 2.25MHZ, 1.25A MONOLITHIC SYNCHRONOUS BUCK REGULATOR LTC3564 DESCRIPTION Demonstration circuit DC1343A is a high efficiency monolithic synchronous buck regulator using a constant frequency, current mode architecture featuring LTC3564. Its high switching frequency of 2.25MHz allows the use of small surface mount inductors and capacitors. Supply current during operation is typically only 20uA, and drops to below 1uA in shutdown. The 2.5V to 5.5V input voltTable 1. age range makes the LTC3564 ideally suited for single Li-Ion battery-powered or 3.3V to 5V input voltage applications. 100% duty cycle provides low dropout operation, extending battery life in portable systems. Automatic Burst Mode® operation increases efficiency at light loads, further extending battery runtime. Gerber files for this circuit are available. Call the LTC Factory. Performance Summary (TA = 25ºC) PARAMETER CONDITION VALUE Input Voltage Output Voltage VOUT 2.5V to 5.5V IOUT=0A to 1.25A VOUT ± 1% Maximum Output Current 1.25A DC Supply Current VIN = 3.3V, VOUT = 1.8V, IOUT = 0A <40µA Nominal Switching Frequency VIN = 3.3V, VOUT = 1.8V, IOUT = 1.25A 2.25MHz QUICK START PROCEDURE The DC1343A is easy to set up to evaluate the performance of the LTC3564. Refer to Figure 2 for the proper measurement equipment setup. 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 the measurement example diagram in Figure 1 for proper scope probe technique. Please follow the procedure outlined below for proper operation. 1. Connect the input power supply to the VIN and GND terminals. Connect the load between the VOUT and GND terminals. 2. Before proceeding to operation, insert jumper shunt XJP1 into the OFF position and insert one jumper shunt into XJP2, XJP3 or XJP4 for voltages of 1.2V, 1.5V, or 1.8V respectively. Set the load output current to less than 1.25A. An optional output voltage can be set by populating resistor RFB6, removing RFB5, and moving the shunt to JP5. 3. Apply 5V at VIN. Measure VOUT; it should read 0V. If desired, one can measure the shutdown supply current at this point. The supply current will be about 1 µA in shutdown. 4. Turn on VOUT by changing shunt XJP1 from the OFF position to the ON position. The output voltage should measure according to the voltage set by the shunt in JP2, JP3, or JP4. 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1343A 2.25MHZ, 1.25A MONOLITHIC SYNCHRONOUS BUCK REGULATOR 5. Vary the input voltage between 2.5V and 5.5V and the output voltage should be within +/1% tolerance. Warning - If the power for the demo board is carried in long leads, the input voltage at the part could “ring”, which could affect the operation of the circuit or even exceed the maximum voltage rating of the IC. To eliminate the ringing, insert a small tantalum capacitor (for instance, AVX part 6. Vary the VOUT load current from 0 to 1.25A, and the output voltage should be within a tolerance of +/- 1%. # TAJW686M010) on the pads between the input power and return terminals on the bottom of the demo board. The (greater) ESR of the tantalum will dampen the (possible) ringing voltage due to the use of long input leads. On a normal, typical PCB, with short traces, the capacitor is not needed. Figure 1. Measuring Input or Output Ripple Figure 2. Proper Measurement Equipment Setup Load Step Response 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1343A 2.25MHZ, 1.25A MONOLITHIC SYNCHRONOUS BUCK REGULATOR Figure 3. Load Step Response Vin = 3.3V, Vout = 1.8V, 1A Load Step (250mA <-> 1.25A), Fsw = 2.25 MHz Trace 3: Output Voltage (100mV/div – AC coupled) Trace 4: Output Current (500mA/div) 3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1343A 2.25MHZ, 1.25A MONOLITHIC SYNCHRONOUS BUCK REGULATOR 4