QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 828 HIGH EFFICIENCY, LOW PROFILE, SYNCHRONOUS BUCK REGULATOR LTC3409 DESCRIPTION Demonstration circuit 828 is a step-down converter, using the LTC3409 monolithic synchronous buck regulator. The DC828 has an input voltage range of 1.6V to 5.5V, and is capable of delivering up to 600mA of output current at a minimum input voltage of 1.8V. The output voltage of the DC828 can be set as low as 0.6V, the reference voltage of the LTC3409. The DC828 can operate in noise sensitive applications, due to the LTC3409 operating in pulse-skipping mode at low load currents. The DC828 is a high efficiency circuit - over 90%, and during shutdown, the DC828 consumes less than 1uA TM typically. In Burst-Mode operation, it consumes only 65uA of quiescent current. Because of the frequencyselect capability of the LTC3409, the DC828 can operate pability of the LTC3409, the DC828 can operate at fixed frequencies of 2.25 MHz or 1.5 MHz, allowing the exclusive use of low profile surface-mount components. The DC828 can also be clocked by an external oscillator, due to a phase-lock loop circuit in the LTC3409. These features, plus the availability of a low profile 8-Lead DFN package, make the DC828 an ideal circuit for use in 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 Minimum Input Voltage CONDITION VALUE 1.6V Maximum Input Voltage Output Voltage VOUT Typical Output Ripple VOUT Output Regulation 5.5V VIN = 1.6V to 5.5V, IOUT1 = 0A to 600 mA 1.2V ±4% VIN = 5V, IOUT1 = 600 mA (20 MHz BW) 20mVP–P Line ±1% Load ±1% Nominal Switching Frequency 1.7 or 2.6 MHz QUICK START PROCEDURE The DC828 demonstration board is easy to set up to evaluate the performance of the LTC3409. For proper measurement equipment configuration, set up the circuit according to the diagram in Figure 1. Before proceeding to test, insert jumper JP3 shunt into the off (lower) position, connecting the RUN pin to ground (GND), which shuts down the circuit. 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 Figure 2 for proper scope probe technique. 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 828 HIGH EFFICIENCY, LOW PROFILE, SYNCHRONOUS BUCK REGULATOR 1. 2. Connect the input power supply and the load to the board. Do not hot-plug Vin or increase Vin over the rated maximum supply voltage of 5.5V, or the part may be damaged. Refer to figure 1 for the proper measurement equipment setup. Insert the shunts in the 1.7 MHz position of jumper JP1, in the Burst-Mode position of jumper JP2, and in the 1.2V position – jumper JP4. 3. Apply 3.3V 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 approximately 1 uA in shutdown. 4. Turn on the circuit by inserting the shunt in jumper JP3 into the ON (upper) position. The output voltage should be regulating. Measure Vout - it should measure 1.2V +/- 2%. 5. Vary the input voltage from 2.5V to 5.5V and adjust the load current from 0 to 600mA. Vout should read between 1.2V +/- 4%. 6. Measure the output ripple voltage at any output current level; it usually will measure less than 20 mVAC. 7. Observe the voltage waveform at the switch node (pin 6 of the IC or one pin of the inductor). Verify the switching frequency is between 0.9 MHz and 2.1 MHz (T = 1.111 us and 0.476 us), and that the switch node waveform is rectangular in shape. When finished, turn off the circuit (connecting the RUN pin to ground) by inserting the shunt in jumper JP3 into the OFF (lower) position. Warning - if the power for the demo board is carried in long leads, the input voltage at the part could “ring”. To eliminate this, insert a small tantalum capacitor (for instance, an AVX part # TAJT226M010R) 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. 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 828 HIGH EFFICIENCY, LOW PROFILE, SYNCHRONOUS BUCK REGULATOR Figure 1. Proper Measurement Equipment Setup Figure 2. Measuring Input or Output Ripple 3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 828 HIGH EFFICIENCY, LOW PROFILE, SYNCHRONOUS BUCK REGULATOR Figure 3. Load Step Response Vin – 1.8V Vout – 1.2V Iout Step – 500 mA Trace 1: Output Voltage (100 mV/div AC) Trace 2: Output Current (500 mA/div) 4 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 828 HIGH EFFICIENCY, LOW PROFILE, SYNCHRONOUS BUCK REGULATOR 5