QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 768 15A POLYPHASE MONOLITHIC SYNCHRONOUS BUCK REGULATOR LTC3415 DESCRIPTION Demonstration Circuit 768 is a 15A high efficiency, simple high power supply only. The DC768 has two phase lockable constant frequency buck converter, in- LTC3415s operating in polyphase operation. Due to the corporating two LTC3415 polyphase monolithic syn- LTC3415 polyphase capability, multiple DC768s can be chronous regulators. The DC768 has an input voltage paralleled for higher current power supplies. Since the range of 2.5V to 5.5V and an output voltage range from parallel LTC3415s operate out-of-phase, the amount of 0.6V to 5V. The reference voltage of 0.6V is +/-1% accu- input and output capacitance required will be minimal. rate, producing a more precise output voltage. The op- The DC768 offers the three standard modes of opera- erating frequency range of the DC768 is either set by the tion: force continuous, pulse-skipping, and Burst- TM LTC3415 internal oscillator to 1.5 MHz, set to 1 MHz or 2 Mode , for those circuits that operate during intervals of MHz by forcing the PLLPF pin to ground or Vin, respec- low output power. Extra features include tracking, for tively, or synchronized to an external clock, with a range easy power supply sequencing, output margining, power between 750 kHz and 2.25 MHz. The DC768 can deliver good, and spread spectrum operation, which signifi- high power for monolithic parts up to 15A of output cantly reduces the peak switching noise emitted from current due to the high current power switches (28 the DC768. All these features make the DC768 perfectly mW of on-state resistance) of the LTC3415. The suited for high current, high power applications, such as LTC3415 also incorporates OPTI-LOOP compensation, notebook or desktop computers. so that the DC768 can be optimized with external com- Design files for this circuit board are available. Call ponents to provide fast transient response over a wide the LTC factory. range of line and load conditions. However, the TM - Burst Mode is a trademark of Linear Technology Corporation LTC3415 has internal compensation for those requiring a Table 1. Performance Summary (T = 25C) A PARAMETER CONDITIONS VALUE Minimum Input Voltage 2.5V Maximum Input Voltage 5.5V 1.2V 3% (1.164V to 1.236V) Output Voltage V Regulation V = 2.5V to 5.5V, I = 0A to 15A 1.5V 3% (1.455V to 1.545V) OUT IN OUT 1.8V 3% (1.746V to 1.854V) Typical Output Ripple V V = 5V, I = 15A (20 MHz BW) <20mV OUT IN OUT PP Burst Mode - V = 3.3V, V = 1.8V <1.5A 0.1A IN OUT Operation Modes Pulse-Skipping - V = 3.3V, V = 1.8V < 5A 0.1A IN OUT Forced Continuous Any Output Current Nominal Switching Frequency 1.5 MHz 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 768 15A POLYPHASE MONOLITHIC SYNCHRONOUS BUCK REGULATOR QUICK START PROCEDURE Demonstration Circuit 768 is easy to set up to evalu- ate the performance of the LTC3415. For proper 3. Vary the input voltage from 2.5V to 5.5V and adjust measurement equipment configuration, set up the the load current from 0 to 15A. Vout should read circuit according to the diagram in Figure 1. Before between 1.2V +/- 3% (1.164V to 1.236V). proceeding to test, make sure the jumper shunts are 4. Measure the output ripple voltage at any output in the appropriate header according to the legend in current level it usually will measure less than 20 Figure 1, except for one exception: insert jumper JP5 mVAC. shunt into the off position, which connects the RUN pin to ground (GND), and thus, shuts down the cir- 5. Observe the voltage waveform at the switch node. cuit. Verify the switching frequency is between 1.3 MHz and 1.7 MHz (T = 0.769 us and 0.588 us), and that NOTE: When measuring the input or output voltage the switch node waveform is rectangular in shape. ripple, care must be taken to avoid a long ground lead on the oscilloscope probe. Measure the input or out- Insert jumper JP5 shunt into the OFF position and move put voltage ripple by touching the probe tip directly the 1.2V Vout shunt into any of the remaining output across the Vin or Vout and GND terminals. See Fig- voltage options: 1.5V or 1.8V. Just as in the 1.2Vout ure 2 for proper scope probe technique. test, the output voltage should read Vout +/- 1.5% toler- ance under static line and load conditions, and another 1. With the DC768 set up according to the proper +/- 1.5% tolerance under dynamic line and load condi- measurement and equipment in Figure 1, apply tions (+/- 3% total). 3.3V at Vin (Do not hot-plug Vin or increase Vin TM over the rated maximum supply voltage of 5.5V, or The Burst-Mode or pulse-skipping operation modes the part may be damaged.). Measure Vout it of the LTC3415 can also be observed now by chang- should read 0V. If desired, one can measure the ing the position of the shunt in header JP7. 1 or 2 shutdown supply current at this point. The supply MHz operating frequencies can be activated by re- current will be approximately 400 uA, or less, in positioning the JP6 shunt. The tables below show shutdown. the extra features, such as margining and spread spectrum. 2. Turn on the circuit by inserting the shunt in header JP5 into the ON position. The output voltage When finished, turn off the circuit (connecting the should be regulating. Measure Vout - it should RUN pin to ground) by inserting the shunt in header measure 1.2V +/- 1.5% (1.182V to 1.218V). JP5 into the OFF position. 2