QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 702 HIGH EFFICIENCY, THINSOT SYNCHRONOUS BUCK REGULATOR LTC3406B-2ES5 DESCRIPTION Demonstration circuit DC702 is a 2.25 MHz step- 1 uA. These features, plus the LTC3406B coming in a down converter, using the LTC3406B monolithic syn- tiny 5-Pin ThinSOT package and having an operating chronous buck regulator. The DC702 has an input frequency of 2.25 MHz (allowing the exclusive use of voltage range of 2.5V to 5.5V, and is capable of deliv- low profile surface mount components), make the ering up to 600 mA of output current at a minimum DC702 an ideal circuit for use in battery-powered, input voltage of 3V. The DC702 is made for noise hand-held applications. sensitive applications, due to the LTC3406B-2 oper- Design files for this circuit board are available. Call ating in pulse-skipping mode at low load currents. the LTC factory. The DC702 is a high efficiency circuit - up to 90%, Burst Mode and ThinSOT are trademarks of Linear Technology Corporation and during shutdown, the DC702 consumes less than Table 1. Performance Summary (T = 25C) A PARAMETER CONDITION VALUE Minimum Input Voltage 2.5V Maximum Input Voltage 5.5V 1.8V 2% Output Voltage V V = 2.5V to 5.5V, I = 0A to 600 mA OUT IN OUT Typical Output Ripple V V = 5V, I = 600 mA (20 MHz BW) 20mV OUT IN OUT PP Line 1% Output Regulation Load 1% Nominal Switching Frequency 2.25 MHz QUICK START PROCEDURE The DC702 demonstration circuit is easy to set up to urement equipment setup and follow the procedure evaluate the performance of the LTC3406B-2. One below: word of caution: when the board is right-side up (the NOTE: When measuring the input or output voltage title is legible at the top of the board), the output volt- ripple, care must be taken to avoid a long ground lead age turret is on the left side of the board, and the in- on the oscilloscope probe. Measure the input or out- put voltage turret is on the right side of the board. put voltage ripple by touching the probe tip directly Set up the circuit appropriately. Before proceeding to across the Vin or Vout and GND terminals. See Fig- test, insert jumper JP1 into the upper position, con- ure 2 for proper scope probe technique. necting the RUN pin to ground (GND), which shuts down the circuit. Refer to Figure 1 for proper meas- 1QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 702 HIGH EFFICIENCY, THINSOT SYNCHRONOUS BUCK REGULATOR 1. Connect the input power supply to the Vin and 5. Vary the input voltage from 2.5V to 5.5V and adjust GND terminals on the right-side of the board. Do the load current from 0 to 600mA. The output volt- not hot-plug Vin or increase Vin over the rated age should be regulating. Measure the output rip- maximum supply voltage of 5.5V, or the part may ple voltage at any output current level it should be damaged. measure less than 20 mVAC. 2. Connect the load between the Vout and GND ter- 6. Observe the voltage waveform at the switch node minals on the left-side of the board. (pin 3). Verify the switching frequency is between 1.8 MHz and 2.7 MHz (T = 0.555 us and 0.370 us), 3. Apply 3.3V at Vin. Measure Vout it should read and that the switch node waveform is rectangular 0V. If desired, one can measure the shutdown in shape. supply current at this point. The supply current will be approximately 1 uA in shutdown. When finished, turn off the circuit (connecting the RUN pin to ground) by inserting the JP1 jumper into 4. Turn on the circuit by connecting the RUN pin to the OFF (upper) position. Vin or inserting the JP1 jumper into the ON (lower) position. Measure Vout - it will measure approxi- mately 1.8V. Warning - if long leads are used to power the demo circuit, the input voltage at the part could ring. To elimi- nate this, insert a small tantalum capacitor (for instance, an AVX part TAJW226M010R) 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. If more efficiency is desired from the demo circuit, replace the stock inductor, a Taiyo Yuden part LQLBC2518M2R2M, with a Murata inductor, LQH32CN2R2M11. Due to its larger size, the Murata inductor has lower DCR than the Taiyo Yuden inductor, thus has less power dissipation. 2